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REVIEW |
1 Department of Oral Health and Diagnostic Sciences, School of Dental Medicine, University of Connecticut, 263 Farmington Ave., Farmington, CT 06030-1710, USA; and
2 Department of General Dentistry, School of Dentistry, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78229-3900, USA
* corresponding author, adongari{at}uchc.edu
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONEPIDEMIOLOGYVIRULENCEHOST-PATHOGEN INTERACTIONSANTIFUNGAL RESISTANCECONCLUSIONS AND FUTURE...REFERENCES |
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KEY WORDS: oral candidiasis • C. glabrata
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONEPIDEMIOLOGYVIRULENCEHOST-PATHOGEN INTERACTIONSANTIFUNGAL RESISTANCECONCLUSIONS AND FUTURE...REFERENCES |
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C. glabrata is increasingly prevalent in systemic infections in recent years (Clark and Hajjeh, 2002; Hajjeh et al., 2004). This is extremely important, since, compared with infection with other non-albicans Candida, the mortality rate of C. glabrata infections is the highest (Abi-Said et al., 1997; Krcmery, 1999). More specifically, the mortality associated with C. glabrata bloodstream infection is around 50% in cancer patients and up to 100% in bone marrow transplant patients (Anaissie et al., 1992; Goodman et al., 1992; Krcmery et al., 1998). Surprisingly, despite this high mortality rate, C. glabrata demonstrates low virulence in animal models of infection (Arendrup et al., 2002).
Oral candidiasis is a common opportunistic infection in immunocompromised populations (Samaranayake and MacFarlane, 1982). C. albicans is still considered the major etiologic agent in this infection and accounts for 70% to 80% of organisms isolated from oral mucosal lesions. However, in recent years, C. glabrata has emerged as a notable pathogenic agent in the oral mucosa, either as a co-infecting agent with C. albicans (Redding et al., 1999, 2002, 2004), or as the sole detectable species from oral lesions (Masia Canuto et al., 2000; Redding et al., 2002, 2004). In addition, C. glabrata-associated oropharyngeal candidiasis infections in HIV and cancer patients tend to be more severe and more difficult to treat than infections due solely to C. albicans (Masia Canuto et al., 2000; Redding et al., 2000, 2002, 2004). Despite the fact that oral Candida infections are not associated with mortality, they are a significant source of morbidity, and trigger chronic pain or discomfort upon mastication, which may limit nutrition intake in immunocompromised or elderly individuals (Redding et al., 2000; Olmos et al., 2005).
Although C. glabrata is one of the most commonly documented species in all candidiasis cases, is extremely difficult to treat (Willocks et al., 1991; Hitchcock et al., 1993), and is associated with systemic infections having a high mortality rate (Krcmery, 1999; Redding et al., 1999; Redding, 2001), studies on this organism have been sporadic in the older literature, and have just started to increase in recent years. As an emerging oral candidiasis pathogen, C. glabrata recently caught the attention of mycology researchers and clinical scientists. Therefore, knowledge about the pathogenesis and the mechanisms of host defense against this organism is slowly increasing. In this review, while comparing with C. albicans wherever possible, we will discuss the prevalence, virulence, host-pathogen interactions, antifungal resistance, and other survival strategies of C. glabrata in the oral mucosa.
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EPIDEMIOLOGY |
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TOPABSTRACTINTRODUCTIONEPIDEMIOLOGYVIRULENCEHOST-PATHOGEN INTERACTIONSANTIFUNGAL RESISTANCECONCLUSIONS AND FUTURE...REFERENCES |
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In recent years, several molecular genotypic approaches have been developed for fast and accurate identification of C. glabrata in vitro. The majority of these molecular procedures include amplification of C. glabrata-specific gene sequences by PCR, restriction fragment length polymorphism (RFLP) (Panackal et al., 2006), or randomly amplified polymorphic DNA (RAPD) methods (Valerio et al., 2006). The amplification of DNA sequences by the extension of C. glabrata-specific oligonucleotide primers has been successfully applied in the rapid identification of C. glabrata in vitro (Sullivan et al., 1996). Moreover, primers, which are specifically complementary to a region of the C. glabrata lanostero-
-demethylase, have been developed to detect DNA purified from this organism (Burgener-Kairuz et al., 1994). Other non-PCR-based genetic typing approaches include tRNA profile analysis, which is based on the different electrophoretic patterns of total cellular tRNA among Candida species (Santos et al., 1994), and Fourier transformed-infrared microspectroscopy, which also permits a detailed analysis of the structure of C. glabrata cells (Essendoubi et al., 2005). To distinguish various strains of C. glabrata, investigators have used karyotypic analysis with comparison of the patterns of chromosomal DNAs. The disadvantages of this procedure include the requirement for expensive equipment as well as the tediousness of DNA preparation. Gupta et al.(2004) applied DNA fingerprint analysis to identify several C. glabrata strains, using short oligonucleotide probes complementary to the repeated microsatellite sequences in C. glabrata genomes. This technique is so sensitive that minor polymorphisms among closely related C. glabrata strains can be detected and distinguished (Sullivan et al., 1993). Although several new molecular means of identification of C. glabrata have been developed, most of them are extremely laborious and cannot be used in large-scale epidemiologic studies. The increasing morbidity and high mortality of C. glabrata systemic infections in immunocompromised populations require the development of new techniques for rapid identification of this organism from clinical specimens with high precision and sensitivity.
(b) Epidemiology of Oral C. glabrata Carriage
Candida colonization of the oral cavity is one of the most frequently identified risk factors for oral infections (Oksala, 1990; Grimoud et al., 2003, 2005); therefore, the oral asymptomatic carriage rates of C. glabrata in different populations will be reviewed first. C. glabrata has been isolated from various oral sites, including buccal and palatal mucosa, dentures, tongue, dental plaque, and subgingival flora (Bagg et al., 2003; Portela et al., 2004; Rasool et al., 2005). It is frequently isolated from the oral cavity with other Candida species, with the most common combination being C. glabrata and C. albicans.
The oral carriage rate of Candida spp. has been suggested to be a function of the aging process from birth to death (Russell and Lay, 1973; Kleinegger et al., 1996), with old age predisposing to increased oral Candida colonization (Lockhart et al., 1999). Although C. albicans remains the primary Candida spp. isolated from the oral cavities in all age groups, several studies demonstrate that colonization of the oral cavity by C. glabrata increases with increasing age (Lockhart et al., 1999; Qi et al., 2005). In one study of 273 young, healthy individuals (from neonate to 21 yrs old), it was found that the frequency of C. glabrata oral carriage increased with increasing age, while the opposite was true of C. albicans (Qi et al., 2005). In particular, the proportion of individuals carrying C. glabrata rose from 0% in the neonatal group to 32.5% in the 18- to 21-year-old group. One of the intriguing findings of this study was that the colonization frequency of C. glabrata was even higher than that of C. albicans (27.5%) in the 18- to 21-year-old group, which was the oldest group in this study. Moreover, an increase in the multiplicity of Candida species co-isolated from the oral cavities with increasing age was also found in this study (Qi et al., 2005). In another study, Lockhart and colleagues reported that C. glabrata was the second most frequently isolated species after C. albicans in the elderly with or without dentures, in a comparison of 93 individuals in three age groups (60 – 69 yrs, 70 – 79 yrs, and 
80 yrs). For individuals wearing dentures, the frequency of C. glabrata carriage rose from 36% in the 70- to 79-year-old group to 58% in the 80-year-old group. For individuals without dentures, C. glabrata was isolated from the oral cavities of 29% of the individuals only in the 80-year-old age group (Lockhart et al., 1999).
As with C. albicans, immunosuppression and antibiotic therapy are also possible risk factors for increased C. glabrata oral carriage. Indeed, the high prevalence of C. glabrata in the oral flora of patients with diabetes mellitus, advanced cancer, and HIV infection has been reported in several studies (Fongsmut et al., 1998; Masia Canuto et al., 2000; Redding et al., 2002, 2004; Bagg et al., 2003). In diabetic individuals, C. glabrata has been identified as the second most frequently isolated species after C. albicans, and accounts for up to 9.4% of all Candida oral isolates from persons with diabetes (Fongsmut et al., 1998; Kadir et al., 2002). Bagg and coworkers isolated yeasts from the mouths of 139 patients with advanced cancer. In this study, 22.7% were orally colonized with C. glabrata, which was the most prevalent non-albicans Candida species. More importantly, 72% of C. glabrata isolates were resistant to both fluconazole and itraconazole, two of the mainstream antifungals in clinical practice (Bagg et al., 2003). In another study involving patients with advanced cancer, the frequency of C. glabrata oral isolation was 18%, which again was the highest among non-albicans Candida species (Davies et al., 2002). In a study of 179 HIV-positive individuals, C. glabrata was the most frequent non-albicans Candida colonizer in the oropharyngeal mucosa, with an isolation rate of 45% (Masia Canuto et al., 2000). Recently, we conducted a study to assess the prevalence of oral Candida colonization in 63 solid organ transplant recipients and found that C. glabrata was the most frequently isolated non-albicans Candida species, isolated from 16.6% of the transplant carriers and 0% of the healthy controls (Dongari-Bagtzoglou et al., in review).
(c) Epidemiology of Oral C. glabrata Infection
Candidiasis is the most common oral fungal infection in humans (Muzyka, 2005). In recent years, although C. albicans remains the most common cause of oral candidiasis, the proportion of cases in which C. glabrata has been isolated is increasing. As many as 71% of persons with C. glabrata oral infections also harbor other Candida species (Vazquez, 1999). Redding et al. reported the emergence of C. glabrata infection in individuals receiving radiation for head and neck cancer (Redding et al., 2002, 2004). In these reports, C. glabrata was isolated from all infected individuals, either as a single or mixed infecting agent. Some of these persons had received prophylactic fluconazole, which was postulated to have applied selective pressure against C. albicans, thereby allowing C. glabrata to overgrow in these lesions. Due to decreased susceptibility to fluconazole, C. glabrata-associated oral candidiasis required higher doses of this antifungal to be successfully treated (Redding et al., 2002, 2004). In addition, Masia Canuto and co-workers reported that C. glabrata was the most frequent non-albicans Candida species isolated as a single infecting organism in oral pseudomembranous candidiasis in HIV-positive individuals (Masia Canuto et al., 2000).
Denture use has been demonstrated to be one of the predisposing conditions of oral candidiasis (Berdicevsky et al., 1980; Ohman et al., 1995; Lockhart et al., 1999). Compared with C. albicans, C. glabrata demonstrated a two-fold greater tendency to adhere to denture acrylic surfaces in vitro (Luo and Samaranayake, 2002). With this high propensity to adhere to denture surfaces, it is not surprising that C. glabrata has been identified as the predominant yeast isolated from dentures in elderly persons with chronic atrophic candidiasis (CAC) (Wilkieson et al., 1991). By attaching to the surfaces of dentures, C. glabrata may protect itself from the relatively high pH, flushing, and antimicrobial activities of saliva (Brandtzaeg et al., 1995; Situ and Bobek, 2000; Feng et al., 2005).
(d) Epidemiology of C. glabrata Infection in Non-oral Sites
As noted previously, C. glabrata is emerging as a pathogenic species not only in oral infections, but also in candidiasis at other sites of the human body. In vulvo-vaginal candidiasis (VVC), C. glabrata has been identified as the most dominant non-albicans Candida species, accounting for up to 34.5% of all isolates from VVC lesions (Gultekin et al., 2005; Ozcan et al., 2006). In urinary tract candidiasis, C. glabrata has been recovered as the second most frequent species after C. albicans (Schelenz and Gransden, 2003; Mujica et al., 2004). In addition, C. glabrata has been identified as the only non-albicans Candida species that has increased in frequency as a cause of bloodstream infection (BSI) over the past decade (Hajjeh et al., 2004). According to the results of an early surveillance study conducted in the beginning of the 1990s, C. glabrata was the fourth most common Candida BSI species, following C. albicans, C. parapsilosis, and C. tropicalis (reviewed in Fidel et al., 1999). Subsequent surveillance studies showed that the proportion of BSI due to C. glabrata increased from 14% to 18% in the USA during a 10-year period from 1992 through 2001 (Pfaller and Diekema, 2004). Moreover, the findings of two other independent studies demonstrated that C. glabrata ranked as the second most common Candida species, and accounted for up to 24% of all Candida BSI in the United States from 1997 to 2001 (Diekema et al., 2002; Pfaller et al., 2002). In a more recent study that examined Candida species distribution of 6082 BSI isolates, C. glabrata was detected as the second most prevalent Candida species among Candida isolates, and the USA was one of the countries in which C. glabrata was the most common cause of BSI (18.3%) (Pfaller and Diekema, 2004). Nationally, a great deal of variation in the frequency of C. glabrata as a cause of BSI was found among the nine USA census regions. The lowest frequency of C. glabrata causing BSI was observed in the South West Central region (11.7%), and the highest frequency was observed in the New England region (37.3%) (Pfaller and Diekema, 2004). Interestingly, the lowest frequency of C. glabrata BSI and the highest fluconazole susceptibility of C. glabrata BSI isolates (84%) were found in one region (Pfaller et al., 2002; Pfaller and Diekema, 2004), South West Central, suggesting that simple drug pressure was not the major cause of the increased prevalence of C. glabrata in this region. Worldwide, C. glabrata was reported to be responsible for approximately 15% of BSI overall. It was the most common cause of BSI in Canada (20.1%) and least common in Europe (13%) and Latin America (7.5%) (Pfaller and Diekema, 2004).
The recent emergence of C. glabrata as a pathogen in both mucosal and systemic candidiasis can be attributed to several factors. One of these is the widespread prophylactic use of antifungal agents in chronically immunosuppressed populations. Having an innate resistance to most antifungals (Willocks et al., 1991; Hitchcock et al., 1993), C. glabrata can survive through the most typical antifungal regimens and outgrow other species in mixed infections. This antifungal-driven selection process may account for the high level of oral isolation of this organism in persons with advanced cancer who are at high risk for fungal infection and are consequently using prophylactic antifungals. However, this phenomenon cannot account for the higher prevalence of this species in other susceptible populations who are not routinely placed on prophylactic antifungal treatment, such as medically stable transplant patients or the elderly. In these categories, chronic immunosuppression by pharmacological treatment or aging may create a more permissive host environment for the overgrowth of this species, which is normally vulnerable to host immunity.
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VIRULENCE |
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TOPABSTRACTINTRODUCTIONEPIDEMIOLOGYVIRULENCEHOST-PATHOGEN INTERACTIONSANTIFUNGAL RESISTANCECONCLUSIONS AND FUTURE...REFERENCES |
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. Compared with C. albicans, C. glabrata demonstrated relatively lower virulence and pathogenicity in animal models (Fidel et al., 1999). So far, only two animal models of mucosal C. glabrata infections have been reported. One is C. glabrata vaginitis in non-obese diabetic (NOD) mice (reviewed in Fidel et al., 1996), and the other is C. glabrata intestinal colonization in CF1 mice (Stiefel et al., 2004). Unfortunately, there is currently no animal model of C. glabrata-induced oral candidiasis. Indeed, the lack of an animal model of oral infection has hindered the study of the virulence of this organism thus far.
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(a) Adherence
As the first step in colonization and persistence in the host, adherence was proposed to be of prime importance in the virulence of Candida (Cannon et al., 1995). The adhesion of several Candida species to monolayers of human gingival epithelial cells has been quantitatively evaluated in vitro. Compared with C. albicans and C. tropicalis, C. glabrata exhibited lower capacity to adhere to oral gingival epithelial cells (Nikawa et al., 1995; Biasoli et al., 2002). The low adherence of C. glabrata to oral epithelial cells might be due to the lack of true hyphal transformation, which plays an important role in C. albicans adherence and persistence (Nikawa et al., 1995; Villar et al., 2004).
At the genetic level, adherence of C. glabrata to host epithelial tissue is largely mediated by the EPA (Epithelial Adhesion) family of genes. The C. glabrata genome encodes several EPA genes (Cormack et al., 1999). C. glabrata strain BG2, a clinical human vaginitis isolate that was also virulent in a murine model of vaginitis (Fidel et al., 1996), adheres to human epithelial cells (HEp2) in vitro via an EPA1-encoded lectin, which recognizes host N-acetyl lactosamine-containing glycoconjugates (Cormack et al., 1999). When growing in laboratory broth, all EPA genes, except EPA1, are expressed at low levels, and deletion of EPA1 alone can reduce adherence to background levels. Despite the significant reduction of adherence in vitro, no difference in either initial colonization or persistence was found between the EPA1 and epa1
strains in murine vaginal and gastro-intestinal tract infections (Cormack et al., 1999). The absence of reduced colonization in epa1 strains in vivo was suggested to be due to the redundancy of adhesins in C. glabrata.
The ability of Candida isolates to form a biofilm on the surfaces of dentures correlates with their adherence capability. Studies on Candida colonization on denture surfaces demonstrated that biofilm formation of C. glabrata GDH2269 was promoted in an increased serum environment, implying that oral inflammation induced by denture plaque would facilitate C. glabrata colonization on these surfaces (Nikawa et al., 2000). Moreover, cell-surface hydrophobicity (CSH) has been shown to promote C. glabrata adherence to denture acrylic surfaces (Luo and Samaranayake, 2002). Compared with C. albicans, C. glabrata demonstrated a four-fold greater CSH value and a two-fold greater tendency to adhere to denture acrylic surfaces (Luo and Samaranayake, 2002).
By adhering to denture surfaces, C. glabrata may promote its oral colonization through several mechanisms. First, the space between the denture and the mucous membrane has a relatively low pH value (Budtz-Jørgensen, 1990), which may provide a suitable micro-environment for C. glabrata to proliferate (Sanchez-Vargas et al., 2002). Second, C. glabrata may protect itself from the flushing action of saliva by adhering to the denture surface facing the oral mucosa. Last, by localizing within surface defects of the denture, C. glabrata is relatively protected from the action of antifungal proteins in saliva.
(b) Extracellular Hydrolase Production
Proteinase production is one of the virulence factors associated with the ability of Candida species to cause infections (Hube and Naglik, 2001). In general, extracellular proteinases are divided into four classes: serine, cysteine, metallo, and aspartyl proteinases. All proteinases secreted by Candida spp. belong to the same class of enzyme-secreted aspartyl proteinases (SAPs). The presence of SAP genes has been identified in several Candida species, including C. albicans (Magee et al., 1993), C. tropicalis (Zaugg et al., 2001), C. parapsilosis (Monod et al., 1994), and C. dubliniensis (Gilfillan et al., 1998), but not C. glabrata (reviewed in Kaur et al., 2005). In vitro, C. glabrata does not produce significant levels of extracellular proteinase activity (Chakrabarti et al., 1991). The absence of SAPs or other proteases in C. glabrata may be indicative of an overall lower virulence potential of this organism. Alternatively, this may suggest that C. glabrata pathogenesis is mediated by other unknown hydrolases or virulence factors.
Another class of hydrolases, which have been suggested to contribute to Candida virulence, are phospholipases. Phospholipases are a heterogeneous group of enzymes which hydrolyze one or more ester linkages in glycerophospholipids. So far, there are four different types of phospholipases reported to be secreted by C. albicans: phospholipase A (Barrett-Bee et al., 1985), phospholipase B (Banno et al., 1985), phospholipase C (Pugh and Cawson, 1977), and phospholipase D (Cole et al., 1990; Ibrahim et al., 1995). In addition, lysophospholipase-transacylase and lysophospholipase are also found to be secreted by this organism (Barrett-Bee et al., 1985; Takahashi et al., 1991).
Compared with C. albicans, the role of phospholipase in virulence appears to be less important in C. glabrata (Samaranayake et al., 1994). The production of phospholipases in C. glabrata is controversial. Samaranayake and co-workers screened 41 Candida oral isolates for phospholipase activity by using the egg-yolk-based assay and found that none of the C. glabrata strains produced phospholipases (Samaranayake et al., 1984). These findings were confirmed in another study, where all C. glabrata isolates from vulvo-vaginal candidosis in 98 Irish women were devoid of phospholipase activity (al-Rawi and Kavanagh, 1999).
In contrast to findings in mucosal infections, 41% of C. glabrata isolates from BSI were found to produce phospholipase, as detected by Clancy et al. with both egg-yolk-based and colorimetric assays (reviewed in Ghannoum, 2000). In this study, phospholipase B (PLB) and lysophospholipases (Lyso-PL) accounted for 100% of phospholipase activity in this organism. Furthermore, this study suggested that extracellular phospholipase activity is a virulence factor of C. glabrata. This suggestion was based on the fact that the activity levels of PLB and Lyso-PL were higher in isolates from persistent as compared with those from non-persistent candidemia, and the association between phospholipase activity and persistent candidemia was stronger for C. glabrata than for all other non-albicans Candida species tested. It is important to point out that, even in this study, when compared with C. albicans, C. glabrata secreted significantly smaller amounts of phospholipase in vitro (Clancy et al., 1998).
(c) Phenotypic Switching and Filamentation
Phenotypic switching and hyphal transformation are two important developmental programs that contribute to the pathogenic success of Candida species. Both of these two developmental programs provide Candida with the phenotypic plasticity for rapid response to antifungal treatment and the changing immune response, through the regulation of pathogenic phase-specific genes. Indeed, phenotypic switching in C. albicans has been found at higher frequencies in infecting vs. commensal isolates from the oral cavity (Hellstein et al., 1993). Phenotypic switching of strains isolated form HIV-positive individuals just prior to, during, or after an episode of thrush was also found to increase antifungal drug susceptibilities dramatically (Vargas et al., 2000). In another study, C. dubliniensis oral isolates exhibited high-frequency phenotypic switching and produced numerous colony morphologies (Hannula et al., 2000). So far, there is no report on the phenotypic switching of C. tropicalis or C. parapsilosis.
In contrast to C. albicans and C. dubliniensis, C. glabrata was generally assumed, until recently, to be lacking these two developmental programs, and the absence of hyphae has been used as a major discriminating characteristic in typing C. glabrata among Candida species (Odds et al., 1990, 1997). However, recent studies demonstrated that C. glabrata undergoes spontaneous, reversible, and high-frequency phenotypic switching among white, light brown, dark brown, very dark brown, and irregular ’wrinkle’ colony phenotypes on CuSO4-containing indicator agar plates (Odds et al., 1997; Csank and Haynes, 2000). Like switching in C. albicans, switching in C. glabrata involves regulation at the transcriptional level of phase-specific genes, including a metallotheionin gene (MT-II) and a gene for a hemolysin-like protein (HLP) (Soll, 1992, 1997; Lachke et al., 2000). Furthermore, phenotypic switching of C. glabrata has been found at human vaginal colonization sites, with the dark brown colony as the predominant phenotype (Brockert et al., 2003).
Besides phenotypic switching, filamentation in the form of pseudohyphal formation is also observed in C. glabrata. In one study (Lachke et al., 2002), 62 clinical isolates were cultured on CuSO4-containing agar plates. C. glabrata isolates examined in this study were isolated from various anatomical sites, including the oral cavity, vagina, and blood. Moreover, these C. glabrata isolates were derived from samples collected in multiple countries. The morphology of the cells in the colony centers was examined under the microscope between the 3rd and 12th days after plating. Interestingly, during the first three days, approximately 90% of the cells from white, light brown, dark brown, and very dark brown phenotype colonies expressed the budding yeast phenotype almost exclusively. The proportion of budding cells dropped to 40 – 50% on the 7th day, with an accumulation of cells extending tubes and forming pseudohyphae. Importantly, C. glabrata did not form true hyphae. The tubes formed by C. glabrata were different from the true compartmentalized hyphae, with the characteristic absence of a nucleus and the feature of apical swelling into buds. The high-occurring frequency of pseudohyphal and tube formation among the 62 C. glabrata isolates demonstrated that both switching and filamentation are general characteristics of most strains of C. glabrata (Lachke et al., 2002). Future studies are needed to study the frequency of phenotypic switching in C. glabrata at sites of carriage vs. infection in the oral cavity, to demonstrate the relevance of phenotypic switching in antifungal resistance or the pathogenesis of oral infection.
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HOST-PATHOGEN INTERACTIONS |
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TOPABSTRACTINTRODUCTIONEPIDEMIOLOGYVIRULENCEHOST-PATHOGEN INTERACTIONSANTIFUNGAL RESISTANCECONCLUSIONS AND FUTURE...REFERENCES |
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Induction of cytokine expression in the oral mucosa by C. glabrata has been studied in a reconstituted human epithelial in vitro model (Schaller et al., 2002). This in vitro model, consisting of a transformed human buccal keratinocyte cell line (TR146), was infected with C. albicans SC5314 or a C. glabrata strain originally isolated from a person with oral candidiasis. At the gene level, C. albicans infection up-regulated the expression of various proinflammatory cytokines and chemokines, including interleukin-1 (IL-1), IL-8, tumor necrosis factor (TNF), and granulocyte monocyte colony-stimulating factor (GM-CSF). In contrast to C. albicans, C. glabrata failed to induce significant cytokine responses, with the exception of a weak increase in GM-CSF expression. At the protein level, a much lower expression of IL-8 was found with C. glabrata infection when compared with C. albicans. This study was the first to study cytokine responses of human oral epithelial cells to C. glabrata infection in vitro (Schaller et al., 2002).
Findings in the study by Schaller and co-workers were supported by recent studies from our group, which showed that, with the exception of GM-CSF, the overall proinflammatory cytokine response to C. glabrata is lower than that triggered by C. albicans. Strain differences in eliciting inflammatory cytokine responses were also noted in our study, with lesional isolates from esophageal candidiasis possessing higher cytokine induction capacity than oral commensal isolates (Li et al., in press). Furthermore, using a monolayer as well as a reconstituted in vitro model of the human oral mucosa and multiple C. glabrata strains, we found that even though C. glabrata was able to kill up to 60% of oral epithelial cells in a 36-hour co-culture system, compared with C. albicans, it was less cytotoxic (Fig. 1), and did not invade an in vitro 3-dimensional model of the human oral mucosa (Fig. 2).
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Our previous studies have shown that adhesion of C. albicans to oral epithelial cells is strengthened by yeast-to-hyphae transformation and results in higher proinflammatory cytokine responses (Villar et al., 2004). In accordance with these findings with C. albicans, it has been shown that the disruption of the virulence-moderating gene ACE2 in C. glabrata, which encodes for a transcriptional activator needed for mother-daughter separation, results in defective cell separation and a strikingly pronounced proinflammatory cytokine response in a murine model of disseminated candidiasis. Upon infection with the ace2 mutant, the mice quickly succumbed to severe septic shock, indicated by a sharp rise in circulating inflammatory cytokines (Kamran et al., 2004). Further investigation is needed to address conclusively whether morphotypic transformation due to incomplete cell separation during budding is one of the virulence attributes of certain clinical strains isolated from oral mucosal lesions.
In a study of C. glabrata-induced systemic infection, non-fatal infection was associated with a rapid induction of proinflammatory cytokines (TNF-, IL-12, and IFN-
) in intravenously inoculated mice. Neutralization of endogenous TNF- with specific TNF- monoclonal antibody resulted in a significant C. glabrata replication in vivo, suggesting the important role of TNF- in host defense against systemic candidiasis caused by C. glabrata (Brieland et al., 2001).
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ANTIFUNGAL RESISTANCE |
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TOPABSTRACTINTRODUCTIONEPIDEMIOLOGYVIRULENCEHOST-PATHOGEN INTERACTIONSANTIFUNGAL RESISTANCECONCLUSIONS AND FUTURE...REFERENCES |
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Secreted by the parotid and submandibular glands, histatins (Hsn) are a family of salivary proteins with broad-spectrum antifungal activity (Helmerhorst et al., 1999; Nikawa et al., 2001; Wei and Bobek, 2004). Magainins are a group of cationic antifungal proteins derived from frog dermal glands. In a recent study, the antifungal activity of these two classes of proteins toward several Candida species was compared. Compared with C. glabrata, C. albicans demonstrated significantly higher susceptibility to the fungicidal activity of human histatin-5 (Hsn-5) and magainin 2. Notably, C. glabrata was the only species that demonstrated a remarkable resistance to histatins as well as to magainins among all Candida species tested, including C. kefyr, C. krusei, and C. parapsilosis (Helmerhorst et al., 2005). In contrast to these findings, susceptibility of C. glabrata to Hsn-5 was reported in two other studies. In one study, Hsn-5 was effective against both azole-resistant and azole-sensitive isolates of C. glabrata (Tsai and Bobek, 1997). In another study, both amphotericin B-resistant and amphotericin B-sensitive clinical isolates of C. glabrata were shown to be susceptible to killing by Hsn-5 and two Hsn-5 variants (Situ et al., 2000). One interesting finding in this study was that MUC7 D1 (the N-terminal domain of human salivary mucin MG2), which was quite active against C. albicans, demonstrated even higher efficiency in C. glabrata killing vs. Hsn-5 in vitro. Both Hsn-5 variants and MUC7 D1 exhibited low cytotoxicity against human erythrocytes and high stability in human saliva and serum, indicating the therapeutic potential of these two peptides as topical oral antifungal agents in C. glabrata infections. A similar susceptibility to the candidacidal activity of Hsn-5 and MUC7 D1 was found between azole-resistant and azole-sensitive C. glabrata strains, suggesting that the cellular target of Hsn-5 and MUC7 D1 was different from that of azole-based antifungals. It is known that Hsn-5 internalization by C. albicans is required for candidacidal activity (Helmerhorst et al., 1999; Koshlukova et al., 1999). However, the mechanisms of killing of C. glabrata by salivary histatins and mucins are not known.
In view of the resistance of C. glabrata to antimicrobial proteins, it is interesting that this organism is also innately resistant to azole antifungals. Recent studies have demonstrated that, in addition to having innate resistance, C. glabrata can also acquire drug resistance and become more resistant after selection in the presence of fluconazole (Vanden Bossche et al., 1992). Both innate and acquired antifungal resistance is important to the persistence of this pathogenic organism, especially in areas where fluconazole use is high (Vanden Bossche et al., 1992; Sanglard et al., 1999). One key mechanism used by C. glabrata to develop acquired resistance is to increase azole efflux from the yeast cell through overexpression of two ATP-binding cassette transporters, cdr1 and cdr2 (Sanglard et al., 1999). Moreover, C. glabrata can up-regulate the expression of the CgERG11 gene, which encodes lanosterol 14 demethylase. This enzyme is responsible for the biosynthesis of ergosterol in C. glabrata, which is selectively targeted by azole antifungals (Miyazaki et al., 1998).
Another mechanism utilized by C. glabrata to acquire drug resistance is the loss of mitochondrial function upon drug exposure (Kaur et al., 2004). Mutants defective in mitochondrial assembly and organization exhibited higher levels of fluconazole resistance as compared with wild-type strains. Loss of mitochondrial function has been found to be reversible in both mutants and wild-type strains, and this phenomenon does not necessarily involve loss of the mitochondrial genome. Moreover, the ability to regain mitochondrial function in C. glabrata highly suggests an epigenetic mechanism utilized by this organism to switch between respiratory-competent and -incompetent states. The fluconazole-associated switching may explain the poor correlation between the levels of azole resistance measured in vitro and pharmacologic treatment results in vivo. Clinical isolates, which are sensitive to fluconazole in vitro, may undergo epigenetic switching from the mitochondrial-competent state (fluconazole-susceptible) to the incompetent state (fluconazole-resistant), resulting in the increased resistance to antifungals and the failure of treatment (Kaur et al., 2004).
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CONCLUSIONS AND FUTURE DIRECTIONS |
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TOPABSTRACTINTRODUCTIONEPIDEMIOLOGYVIRULENCEHOST-PATHOGEN INTERACTIONSANTIFUNGAL RESISTANCECONCLUSIONS AND FUTURE...REFERENCES |
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The role of extracellular hydrolases in C. glabrata virulence appears less important when compared with that of C. albicans. Some studies reported that the activity level of phospholipases was higher in C. glabrata isolates from persistent as compared with non-persistent candidemia (Clancy et al., 1998). Future investigation is required for full elucidation of the role of phospholipases in C. glabrata oral infections. Future availability of congenic mutant strains, which differ only in phospholipase synthesis, is expected to facilitate studies in this area.
Strain differences were noted in the ability of C. glabrata to adhere to oral epithelial cells (Biasoli et al., 2002), synthesize phospholipases (Ghannoum, 2000), and trigger cytokine responses (Li et al., in press). In addition, many of these phenotypic characteristics were more pronounced in lesional vs. commensal C. glabrata isolates (Li et al., in press). Such strain-to-strain phenotypic variations may contribute to the difficulty in establishing a role for this organism in pathogenesis.
The reason for the increased presence of C. glabrata in the oral cavities of the elderly remains unknown and requires further investigation. Saliva plays a critical role in oral homeostasis (Atkinson and Baum, 2001) and is affected by aging (Finkelstein et al., 1984; Denny et al., 1991; Wu et al., 1993). Salivation becomes markedly decreased in people over 70 years old (Wilkieson et al., 1991). In addition, an age-related decrease of salivary antifungal molecules—including secretory IgA (Evans et al., 2000; Tanida et al., 2001; Akimoto et al., 2003), histatins (Johnson et al., 2000), lactoferrin (Tanida et al., 2001), transferrin (Tanida et al., 2001), lysozyme (Shugars et al., 2001), and mucins (Denny et al., 1991; Navazesh et al., 1992)—has been reported in the elderly. However, it seems that salivary hypofunction alone cannot explain the overgrowth of C. glabrata at the expense of C. albicans, given the fact that, compared with C. albicans, C. glabrata is more resistant to the anticandidal activity of these salivary proteins (Xu et al., 1999; Situ and Bobek, 2000).
Salivary pH changes in the elderly may be another factor leading to increased oral colonization of C. glabrata. The saliva of elderly people is slightly more acidic compared with that of younger individuals (Lundgren et al., 1996). It has been found that salivary pH functions as a significant environmental signal in determining the virulence of Candida, through differential gene up-regulation (De Bernardis et al., 1998) or modulation of host defenses (Runeman et al., 2000). Increased growth rate, enhanced adherence to epithelial cells, and augmented Sap activity have been reported in C. albicans when this organism was cultured in acidic saliva (reviewed in de Repentigny et al., 2004). Moreover, a low pH enhanced the expression of the C. albicans virulence genes PHR1 and PHR2, resulting in an increased virulence in this organism (De Bernardis et al., 1998). Compared with C. glabrata, C. albicans is more acid-tolerant (Lenander-Lumikari and Johansson, 1995). The growth of C. albicans in human saliva at pH 5 was similar to that of C. glabrata, but was remarkably slower at pH 6 (Lenander-Lumikari and Johansson, 1995). Thus, these findings suggest that the slightly more acidic oral environment in elderly people should favor the overgrowth of C. albicans and not C. glabrata. Moreover, these observations suggest that the increased oral carriage frequency of C. glabrata in the elderly is probably complex and not caused by a single senile change in oral salivary or mucosal function. Studies regarding age-related changes of the oral bacterial flora in the elderly and the interaction of C. glabrata with other oral micro-organisms may provide new clues that could explain the increased presence of this organism in aging individuals.
In conclusion, although C. glabrata has emerged as an important pathogen in oral candidiasis in recent years, little is known about the virulence of this organism and host defenses in the oral mucosa. Future studies are needed to explore the pathogenesis and host-pathogen interactions of C. glabrata in oral candidiasis.
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ACKNOWLEDGMENTS |
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Received February 16, 2006; Accepted July 28, 2006
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REFERENCES |
|---|
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TOPABSTRACTINTRODUCTIONEPIDEMIOLOGYVIRULENCEHOST-PATHOGEN INTERACTIONSANTIFUNGAL RESISTANCECONCLUSIONS AND FUTURE...REFERENCES |
|---|
Akimoto T, Kumai Y, Akama T, Hayashi E, Murakami H, Soma R, et al. (2003). Effects of 12 months of exercise training on salivary secretory IgA levels in elderly subjects. Br J Sports Med 37:76–79.
al-Rawi N, Kavanagh K (1999). Characterisation of yeasts implicated in vulvovaginal candidosis in Irish women. Br J Biomed Sci 56:99–104.[ISI][Medline]
Anaissie EJ, Vartivarian SE, Abi-Said D, Uzun O, Pinczowski H, Kontoyiannis DP (1992). Fluconazole versus amphotericin B in the treatment of hematogenous candidiasis: a matched cohort study. Am J Med 101:170–176.
Anhalt E, Alvarez J, Berg R (1986). Candida glabrata meningitis. South Med J 79:916.[ISI][Medline]
Arendrup M, Horn T, Frimodt-Moller N (2002). In vivo pathogenicity of eight medically relevant Candida species in an animal model. Infection 30:286–291.[ISI][Medline]
Atkinson JC, Baum BJ (2001). Salivary enhancement: current status and future therapies. J Dent Educ 65:1096–1101.[Abstract]
Bagg J, Sweeney MP, Lewis MA, Jackson MS, Coleman D, Al MA, et al. (2003). High prevalence of non-albicans yeasts and detection of anti-fungal resistance in the oral flora of patients with advanced cancer. Palliat Med 17:477–481.
Banno Y, Yamada T, Nozawa Y (1985). Secreted phospholipases of the dimorphic fungus, Candida albicans; separation of three enzymes and some biological properties. Sabouraudia 23:47–54.[ISI][Medline]
Barousse MM, Steele C, Dunlap K, Espinosa T, Boikov D, Sobel JD, et al. (2001). Growth inhibition of Candida albicans by human vaginal epithelial cells. J Infect Dis 184:1489–1493.[ISI][Medline]
Barrett-Bee K, Hayes Y, Wilson RG, Ryley JF (1985). A comparison of phospholipase activity, cellular adherence and pathogenicity of yeasts. J Gen Microbiol 131:1217–1221.[Medline]
Berdicevsky I, Ben-Aryeh H, Szargel R, Gutman D (1980). Oral candida of asymptomatic denture wearers. Int J Oral Surg 9:113–115.[ISI][Medline]
Biasoli MS, Tosello ME, Magaro HM (2002). Adherence of Candida strains isolated from the human gastrointestinal tract. Mycoses 45:465–459.[ISI][Medline]
Brandtzaeg P, Gabrielsen TO, Dale I, Muller F, Steinbakk M, Fagerhol MK (1995). The leucocyte protein L1 (calprotectin): a putative nonspecific defence factor at epithelial surfaces. Adv Exp Med Biol 371(A):201–206.
Brieland J, Essig D, Jackson C, Frank D, Loebenberg D, Menzel F, et al. (2001). Comparison of pathogenesis and host immune responses to Candida glabrata and Candida albicans in systemically infected immunocompetent mice. Infect Immun 69:5046–5055.
Brockert PJ, Lachke SA, Srikantha T, Pujol C, Galask R, Soll DR (2003). Phenotypic switching and mating type switching of Candida glabrata at sites of colonization. Infect Immun 71:7109–7118.
Budtz-Jorgensen E (1990). Candida-associated denture stomatitis and angular cheilitis. In: Oral candidosis. Samaranayake LP, Wallace T, editors. London: Wright, pp. 156-183.
Burgener-Kairuz P, Zuber JP, Jaunin P, Buchman TG, Bille J, Rossier M (1994). Rapid detection and identification of Candida albicans and Torulopsis (Candida) glabrata in clinical specimens by species-specific nested PCR amplification of a cytochrome P-450 lanosterol-alpha-demethylase (L1A1) gene fragment. J Clin Microbiol 32:1902–1907.
Cannon RD, Hommes AR, Mason AB, Monk BC (1995). Oral Candida: clearance, colonization, or candidiasis? J Dent Res 74:1152–1161.
Chakrabarti A, Nayak N, Talwar P (1991). In vitro proteinase production by Candida species. Mycopathologia 114:163–168.[ISI][Medline]
Clark TA, Hajjeh RA (2002). Recent trends in the epidemiology of invasive mycoses. Curr Opin Infect Dis 15:569–674.[ISI][Medline]
Cole GT, Lynn KT, Seshan KR (1990). An animal model for oropharyngeal, esophageal and gastric candidosis. Mycoses 33:7–19.[ISI][Medline]
Cormack BP, Ghori N, Falkow S (1999). An adhesin of the yeast pathogen Candida glabrata mediating adherence to human epithelial cells. Science 285:578–582.
Coutte L, Alonso S, Reveneau N, Willery E, Quatannens B, Locht C, et al. (2003). Role of adhesin release for mucosal colonization by a bacterial pathogen. J Exp Med 197:735–742.
Cross LJ, Williams DW, Sweeney CP, Jackson MS, Lewis MA, Bagg J (2004). Evaluation of the recurrence of denture stomatitis and Candida colonization in a small group of patients who received itraconazole. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 97:351–358.[ISI][Medline]
Csank C, Haynes K (2000). Candida glabrata displays pseudohyphal growth. FEMS Microbiol Lett 189:115–120.[ISI][Medline]
Davies AN, Brailsford S, Broadley K, Beighton D (2002). Oral yeast carriage in patients with advanced cancer. Oral Microbiol Immunol 17:79–84.[ISI][Medline]
De Bernardis F, Muhlschlegel FA, Cassone A, Fonzi WA (1998). The pH of the host niche controls gene expression in and virulence of Candida albicans. Infect Immun 66:3317–3325.
de Repentigny L, Lewandowski D, Jolicoeur P (2004). Immunopathogenesis of oropharyngeal candidiasis in human immunodeficiency virus infection. Clin Microbiol Rev 17:729–759.
Denny PC, Denny PA, Klauser DK, Hong SH, Navazesh M, Tabak LA (1991). Age-related changes in mucins from human whole saliva. J Dent Res 70:1320–1327.
Diekema DJ, Messer SA, Brueggemann AB, Coffman SL, Doern GV, Herwaldt LA, et al. (2002). Epidemiology of candidemia: 3-year results from the emerging infections and the epidemiology of Iowa organisms study. J Clin Microbiol 40:1298–1302.
Dongari-Bagtzoglou A, Dwivedi P, Ioannidou E, Hull D, Burleson J (2007). Oral Candida infection and colonization in transplant recipients. J Oral Pathol Med (in press).
El-Azizi MA, Starks SE, Khardori NJ (2004). Interactions of Candida albicans with other Candida spp. and bacteria in the biofilms. Appl Microbiol 96:1067–1073.
Essendoubi M, Toubas D, Bouzaggou M, Pinon JM, Manfait M, Sockalingum GD (2005). Rapid identification of Candida species by FT-IR microspectroscopy. Biochim Biophys Acta 1724:239–247.[Medline]
Evans P, Der G, Ford G, Hucklebridge F, Hunt K, Lambert S (2000). Social class, sex, and age differences in mucosal immunity in a large community sample. Brain Behav Immun 14:41–48.[ISI][Medline]
Feng Z, Jiang B, Chandra J, Ghannoum M, Nelson S, Weinberg A (2005). Human beta-defensins: differential activity against Candidal species and regulation by Candida albicans. J Dent Res 84:445–450.
Fidel PL Jr, Cutright JL, Tait L, Sobel JD (1996). A murine model of Candida glabrata vaginitis. J Infect Dis 173:425–431.[ISI][Medline]
Fidel PL Jr, Vazquez JA, Sobel JD (1999). Candida glabrata: review of epidemiology, pathogenesis, and clinical disease with comparison to C. albicans. Clin Microbiol Rev 12:80–96.
Finkelstein MS, Tanner M, Freedman ML (1984). Salivary and serum IgA levels in geriatric outpatient population. J Clin Immunol 4:85–91.[ISI][Medline]
Fongsmut T, Deerochanawong C, Prachyabrued W (1998). Intraoral Candida in Thai diabetes patients. J Med Assoc Thai 81:449–453.[Medline]
Garcia de Viedma D, Lorenzo G, Cardona PJ, Rodriguez NA, Gordillo S, Serrano MJ, et al. (2005). Association between the infectivity of Mycobacterium tuberculosis strains and their efficiency for extrarespiratory infection. J Infect Dis 192:2059–2065.[ISI][Medline]
Gilfillan GD, Sullivan DJ, Haynes K, Parkinson T, Coleman DC, Gow NA (1998). Candida dubliniensis: phylogeny and putative virulence factors. Microbiology 144(Pt 4):829–838.[Abstract]
Ghannoum MA (2000). Potential role of phospholipases in virulence and fungal pathogenesis. Clin Microbiol Rev 13:122–143.
Goodman JL, Winston DJ, Greenfield RA, Chandrasekar PH, Fox B, Kaizer H (1992). A controlled trial of fluconazole to prevent fungal infections in patients undergoing bone marrow transplantation. N Engl J Med 326:845–851.[Abstract]
Grimoud AM, Marty N, Bocquet H, Andrieu S, Lodter JP, Chabanon G (2003). Colonization of the oral cavity by Candida species: risk factors in long-term geriatric care. J Oral Sci 45:51–55.[Medline]
Grimoud AM, Lodter JP, Marty N, Andrieu S, Bocquet H, Linas MD, et al. (2005). Improved oral hygiene and Candida species colonization level in geriatric patients. Oral Dis 11:163–169.[ISI][Medline]
Gultekin B, Yazici V, Aydin N (2005). Distribution of Candida species in vaginal specimens and evaluation of CHROMagar Candida medium. Mikrobiyol Bul 39:319–324 [article in Turkish].[Medline]
Gupta N, Haque A, Lattif AA, Narayan RP, Mukhopadhyay G, Prasad R (2004). Epidemiology and molecular typing of Candida isolates from burn patients. Mycopathologia 158:397–405.[ISI][Medline]
Hajjeh RA, Sofair AN, Harrison LH, Lyon GM, Arthington-Skaggs BA, Mirza SA, et al. (2004). Incidence of bloodstream infections due to Candida species and in vitro susceptibilities of isolates collected from 1998 to 2000 in a population-based active surveillance program. J Clin Microbiol 42:1519–1527.
Hannula J, Saarela M, Dogan B, Paatsama J, Koukila-Kahkola P, Pirinen S, et al (2000). Comparison of virulence factors of oral Candida dubliniensis and Candida albicans isolates in healthy people and patients with chronic candidosis. Oral Microbiol Immunol 15:238–244.[ISI][Medline]
Härder J, Bartels J, Christophers E, Schroder JM (1997). A peptide antibiotic from human skin. Nature 387:861.[Medline]
Härder J, Bartels J, Christophers E, Schroder JM (2001). Isolation and characterization of human beta-defensin-3, a novel human inducible peptide antibiotic. J Biol Chem 276:5707–5713.
Hellstein J, Vawter-Hugart H, Fotos P, Schmid J, Soll DR (1993). Genetic similarity and phenotypic diversity of commensal and pathogenic strains of Candida albicans isolated from the oral cavity. J Clin Microbiol 31:3190–3199.
Helmerhorst EJ, Breeuwer P, van’t Hof W, Walgreen-Weterings E, Oomen LC, Veerman EC, et al. (1999). The cellular target of histatin 5 on Candida albicans is the energized mitochondrion. J Biol Chem 274:7286–7291.
Helmerhorst EJ, Venuleo C, Beri A, Oppenheim FG (2005). Candida glabrata is unusual with respect to its resistance to cationic antifungal proteins. Yeast 22:705–714.[ISI][Medline]
Hitchcock CA, Pye GW, Troke PF, Johnson EM, Warnock DW (1993). Fluconazole resistance in Candida glabrata. Antimicrob Agents Chemother 37:1962–1965.
Hoover DM, Wu Z, Tucker K, Lu W, Lubkowski J (2003). Antimicrobial characterization of human beta-defensin 3 derivatives. Antimicrob Agents Chemother 47:2804–2809.
Hube B, Naglik J (2001). Candida albicans proteinases: resolving the mystery of a gene family. Microbiology 147(Pt 8):1997–2005.
Ibrahim AS, Mirbod F, Filler SG, Banno Y, Cole GT, Kitajima Y, et al. (1995). Evidence implicating phospholipase as a virulence factor of Candida albicans. Infect Immun 63:1993–1998.
