Elucidating the origins of nosocomial infections with Candida albicans by DNA fingerprinting with the complex probe Ca3

Microbiota signatures associated with invasive Candida albicans infection in the gastrointestinal tract of immunodeficient mice

Candida albicans is a commensal microorganism in the human gut but occasionally causes invasive C. albicans infection (ICA), especially in immunocompromised individuals. Early initiation of antifungal therapy is associated with reduced mortality of ICA, but rapid diagnosis remains a challenge. The ICA-associated changes in the gut microbiota can be used as diagnostic and therapeutic targets but have been poorly investigated. In this study, we utilized an immunodeficient Rag2γc (Rag2-/-il2γc-/-) mouse model to investigate the gut microbiota alterations caused by C. albicans throughout its cycle, from its introduction into the gastrointestinal tract to invasion, in the absence of antibiotics. We observed a significant increase in the abundance of Firmicutes, particularly Lachnospiraceae and Ruminococcaceae, as well as a significant decrease in the abundance of Candidatus Arthromitus in mice exposed to either the wild-type SC5314 strain or the filamentation-defective mutant (cph1/cph1 efg1/efg1) HLC54 strain of C. albicans. However, only the SC5314-infected mice developed ICA. A linear discriminate analysis of the temporal changes in the gut bacterial composition revealed Bacteroides vulgatus as a discriminative biomarker associated with SC5314-infected mice with ICA. Additionally, a positive correlation between the B. vulgatus abundance and fungal load was found, and the negative correlation between the Candidatus Arthromitus abundance and fungal load after exposure to C. albicans suggested that C. albicans might affect the differentiation of intestinal Th17 cells. Our findings reveal the influence of pathogenic C. albicans on the gut microbiota and identify the abundance of B. vulgatus as a microbiota signature associated with ICA in an immunodeficient mouse model.

Candidalysin: Connecting the pore forming mechanism of this virulence factor to its immunostimulatory properties

Candida albicans is a deadly pathogen responsible for millions of mucosal and systemic infections per year. The pathobiology of C. albicans is largely dependent on the damaging and immunostimulatory properties of the peptide candidalysin (CL), a key virulence factor. When CL forms pores in the plasma membrane of epithelial cells, it activates a response network grounded in activation of the epidermal growth factor receptor. Prior reviews have characterized the resulting CL immune activation schemas but lacked insights into the molecular mechanism of CL membrane damage. We recently demonstrated that CL functions by undergoing a unique self-assembly process; CL forms polymers and loops in aqueous solution prior to inserting and forming pores in cell membranes. This mechanism, the first of its kind to be observed, informs new therapeutic avenues to treat Candida infections. Recently, variants of CL were identified in other Candida species, providing an opportunity to identify the residues that are key for CL to function. In this review, we connect the ability of CL to damage cell membranes to its immunostimulatory properties.

Friendly fungi: symbiosis with commensal Candida albicans

Mucosal tissues are constitutively colonized by a wide assortment of host-adapted microbes. This includes the polymorphic fungus Candida albicans which is a primary target of human adaptive responses. Immunogenicity is replicated after intestinal colonization in preclinical models with a surprising array of protective benefits for most hosts, but harmful consequences for a few. The interaction between fungus and host is complex, and traditionally, the masking of antigenic fungal ligands has been viewed as a tactic for fungal immune evasion during invasive infection. However, we propose that dynamic expression of cell wall moieties, host cell lysins, and other antigenic C. albicans determinants is necessary during the more ubiquitous context of intestinal colonization to prime immunogenicity and optimize mammalian host symbiosis.

The Glyoxylate Cycle Is Involved in White-Opaque Switching in Candida albicans

Candida albicans is a commensal yeast that inhabits the gastrointestinal tract of humans. The master regulator of the white-opaque transition WOR1 has been implicated in the adaptation to this commensal status. A proteomic analysis of cells overexpressing this transcription factor (WOR1^OE) suggested an altered metabolism of carbon sources and a phenotypic analysis confirmed this alteration. The WOR1^OE cells are deficient in using trehalose and xylose and are unable to use 2C sources, which is consistent with a reduction in the amount of Icl1, the isocitrate lyase enzyme. The icl1Δ/Δ mutants overexpressing WOR1 are deficient in the production of phloxine B positive cells, a main characteristic of opaque cells, a phenotype also observed in mating type hemizygous mtla1Δ icl1Δ/Δ cells, suggesting the involvement of Icl1 in the adaptation to the commensal state. In fact, icl1Δ/Δ cells have reduced fitness in mouse gastrointestinal tract as compared with essentially isogenic heterozygous ICL1/icl1Δ, but overproduction of WOR1 in an icl1Δ/Δ mutant does not restore fitness. These results implicate the glyoxylate shunt in the adaptation to commensalism of C. albicans by mechanisms that are partially independent of WOR1.

Candida albicans Colonizes and Disseminates to the Gastrointestinal Tract in the Presence of the Microbiota in a Severe Combined Immunodeficient Mouse Model

Candida albicans is the leading cause of candidemia or other invasive candidiasis. Gastrointestinal colonization has been considered as the primary source of candidemia. However, few established mouse models that mimic this infection route are available. In the present study, we established a mouse model of disseminated candidiasis developed through the translocation of Candida from the gut. In this study, we developed a novel C. albicans GI colonization and dissemination animal model by using severe combined immunodeficient Rag2^–/–IL2γc^–/– (Rag2γc) mice, which lack functional T, B, NK cells, and IL2γc-dependent signaling. Rag2γc mice were highly susceptible to C. albicans gastrointestinal infection even in the presence of the gut microbiota. Within 4 weeks post infection, Rag2γc mice showed dose-dependent weight loss and disseminated candidiasis in more than 58% (7/12) of moribund mice. Histological analysis demonstrated abundant hyphae penetrating the mucosa, with significant neutrophilic infiltration in mice infected with wild-type C. albicans but not a filamentation-defective mutant. In moribund Rag2γc mice, the necrotic lesions and disrupted epithelial cells were associated with C. albicans hyphae. Notably, removal of the gut microbiota by antibiotics exacerbated the severity of fungal infection in Rag2γc mice, as demonstrated by elevated fungal burdens and accelerated weight loss and death. Furthermore, higher fungal burden and IL-1β expression were prominently noted in the stomach of Rag2γc mice. In fact, a significant increase in circulating proinflammatory cytokines, including IL-6, TNF-α, and IL-10, indicative of a septic response, was evident in infected Rag2γc mice. Additionally, Rag2γc mice exhibited significantly lower levels of IL-22 but not IFN-γ or IL-17A than wild-type B6 mice, suggesting that IL-22 plays a role in C. albicans gastrointestinal infection. Collectively, our analysis of the Rag2γc mouse model revealed features of C. albicans gastrointestinal colonization and dissemination without the interference from antibiotics or chemotherapeutic agents, thus offering a new investigative tool for delineating the pathogenesis of C. albicans and its cross-talk with the gut microbiota.

Evaluation of Polymorphic Locus Sequence Typing for Candida glabrata Epidemiology

The opportunistic yeast Candida glabratais increasingly refractory to antifungal treatment or prophylaxis and relatedly is increasingly implicated in health care-associated infections. To elucidate the epidemiology of these infections, strain typing is required. Sequence-based typing provides multiple advantages over length-based methods, such as pulsed-field gel electrophoresis (PFGE); however, conventional multilocus sequence typing (targeting 6 conserved loci) and whole-genome sequencing are impractical for routine use. A commercial sequence-based typing service for C. glabratathat targets polymorphic tandem repeat-containing loci has recently been developed. These CgMT-J and CgMT-M services were evaluated with 56 epidemiologically unrelated isolates, 4 to 7 fluconazole-susceptible or fluconazole-resistant isolates from each of 5 center A patients, 5 matched pairs of fluconazole-susceptible/resistant isolates from center B patients, and 7 isolates from a center C patient who responded to then failed caspofungin therapy. CgMT-J and CgMT-M generated congruent results, resolving isolates into 24 and 20 alleles, respectively. Isolates from all but one of the center A patients shared the same otherwise rare alleles, suggesting nosocomial transmission. Unexpectedly, Pdr1 sequencing showed that resistance arose independently in each patient. Similarly, most isolates from center B also clustered together; however, this may reflect a dominant clone since their alleles were shared by multiple unrelated isolates. Although distinguishable by their echinocandin susceptibilities, all isolates from the center C patient shared alleles, in agreement with the previously reported relatedness of these isolates based on PFGE. Finally, we show how phylogenetic clusters can be used to provide surrogate parents to analyze the mutational basis for antifungal resistance.

Clonal Strain Persistence of Candida albicans Isolates from Chronic Mucocutaneous Candidiasis Patients

Chronic mucocutaneous candidiasis (CMC) is a primary immunodeficiency disorder characterised by susceptibility to chronic Candida and fungal dermatophyte infections of the skin, nails and mucous membranes. Molecular epidemiology studies of CMC infection are limited in number and scope and it is not clear whether single or multiple strains inducing CMC persist stably or are exchanged and replaced. We subjected 42 C. albicans individual single colony isolates from 6 unrelated CMC patients to multilocus sequence typing (MLST). Multiple colonies were typed from swabs taken from multiple body sites across multiple time points over a 17-month period. Among isolates from each individual patient, our data show clonal and persistent diploid sequence types (DSTs) that were stable over time, identical between multiple infection sites and exhibit azole resistant phenotypes. No shared origin or common source of infection was identified among isolates from these patients. Additionally, we performed C. albicans MLST SNP genotype frequency analysis to identify signatures of past loss of heterozygosity (LOH) events among persistent and azole resistant isolates retrieved from patients with autoimmune disorders including CMC.

Molecular Diversity of Candida albicans Isolated from Immunocompromised Patients, Based on MLST Method

BACKGROUND

As regards multilocus sequence typing (MLST) method directly analyze the polymorphism within DNA sequences; we performed the first nationwide study on the genotypic relationships of Candida albicans strains obtained from oropharynx and bronchoalveolar lavage (BAL) samples from immunocompromised patients.

METHODS

Fourteen epidemiologically unrelated clinical strains of C. albicans were obtained from three hospitals in Mazandaran Province, Iran (2006 to 2012) from seven patients with pulmonary infections and the rest with oropharyngeal samples of immunocompromised patients. Seven loci of housekeeping genes were sequenced for all fourteen isolates.

RESULTS

MLST was applied to a subset of 14 unrelated isolates. Seventy-one (2.5%) nucleotide sites were found to be variable. Accordingly, 60 different alleles were identified in seven loci among the isolates, among which two new alleles were obtained. Furthermore, 12 independent diploid sequence types (DSTs) including five novel DSTs were identified. The fourteen unrelated isolates were placed in 10 clonal clusters (CC) while two isolates were singletons, by eBURST analysis. Most of the isolates belonged to CC461 of eBURST analysis from the clade 11 and two isolates assigned to CC172 from the clade 15.

CONCLUSION

Pathogen distribution and relatedness for determining the epidemiology of nosocomial infections is highly recommended for pathogen control methods.

Management of invasive candidiasis in nonneutropenic ICU patients

Invasive candidiasis (IC) is a leading cause of morbidity and mortality among nonneutropenic ICU patients and these life-threatening nosocomial infections require early diagnosis and prompt treatment. However, none of the predictive tools are sufficiently accurate to identify high-risk patients and the potential interest of IC prophylactic, empirical and preemptive treatment in the nonneutropenic ICU population has not yet been demonstrated. In the case of nosocomial severe sepsis after necrotizing pancreatitis or upper digestive anastomotic leakage, early probabilistic antifungals are probably indicated. In the remaining ICU surgical and medical patients, prophylactic and empirical strategies are highly debated because they may promote antifungal selective pressure through an overuse of these molecules. In this context, non-culture-based methods such as mannan or β-D glucan or polymerase chain reaction tests are promising. However, none of these tests used alone in ICU patients is sufficiently accurate to avoid overuse of empirical/preemptive treatment. The interest of strategies associating predictive clinical scores and non-culture-based methods still needs to be demonstrated by well-conducted randomized, controlled trials. While awaiting these studies, we consider that probabilist treatment should be stopped earlier if IC is not proven.

Clinical and microbiological investigation of fungemia from four hospitals in China

In this study, fungemia cases from four tertiary hospitals located in Shanghai and Anhui province in China from March 2012 to December 2013 were enrolled to investigate clinical features, species distribution, antifungal susceptibility and strain relatedness. During the study period, 137 non-duplicate cases and their corresponding isolates were collected. Six different genera of fungi were identified, of which Candida spp. were the most common (126/137, 91.97 %), with C. albicans predominating (48/137, 35.03 %). The non-Candida fungi rate reached 8.03 % (11/137), and Pichia spp. was the most common (5/137, 3.65 %). Compared with C. albicans, non-C. albicans fungi-associated fungemia was more likely in younger (p = 0.004) and male patients (χ (2) = 6.2618, p = 0.0123) and patients from ICUs (χ (2) = 6.3783, p = 0.0116). Overall, the susceptible/WT rates of common Candida spp. to fluconazole, itraconazole, voriconazole, flucytosine, amphotericin B and caspofungin were 74.63, 92.31, 93.16, 96.58, 100 and 95.69 %, respectively. C. tropicalis and C. guilliermondii had a low susceptibility to fluconazole: 79.95 and 77.78 %, respectively. No isolates were resistant/WT to caspofungin, but C. parapsilosis and C. guilliermondii had high MIC90 values; 1 and 2 mg/L, respectively. In terms of genotyping, MLST was taken for C. glabrata and C. tropicalis, while microsatellite marker analysis was used for C. albicans and C. parapsilosis. C. glabrata was predominantly clone ST7, accounting for 75 %, while the other isolates showed genetic diversity. Considering the increased proportion of non-C. albicans fungi and the presence of endemic clones of C. glabrata, it is essential to undertake additional surveillance of fungemia.

Resistance of Candida spp. to antifungal drugs in the ICU: where are we now?

Current increases in antifungal drug resistance in Candida spp. and clinical treatment failures are of concern, as invasive candidiasis is a significant cause of mortality in intensive care units (ICUs). This trend reflects the large and expanding use of newer broad-spectrum antifungal agents, such as triazoles and echinocandins. In this review, we firstly present an overview of the mechanisms of action of the drugs and of resistance in pathogenic yeasts, subsequently focusing on recent changes in the epidemiology of antifungal resistance in ICU. Then, we emphasize the clinical impacts of these current trends. The emergence of clinical treatment failures due to resistant isolates is described. We also consider the clinical usefulness of recent advances in the interpretation of antifungal susceptibility testing and in molecular detection of the mutations underlying acquired resistance. We pay particular attention to practical issues relating to ICU patient management, taking into account the growing threat of antifungal drug resistance.

Candida colonization index and subsequent infection in critically ill surgical patients: 20 years later

Introduction

For decades, clinicians dealing with immunocompromised and critically ill patients have perceived a link between Candida colonization and subsequent infection. However, the pathophysiological progression from colonization to infection was clearly established only through the formal description of the colonization index (CI) in critically ill patients. Unfortunately, the literature reflects intense confusion about the pathophysiology of invasive candidiasis and specific associated risk factors.

Methods

We review the contribution of the CI in the field of Candida infection and its development in the 20 years following its original description in 1994. The development of the CI enabled an improved understanding of the pathogenesis of invasive candidiasis and the use of targeted empirical antifungal therapy in subgroups of patients at increased risk for infection.

Results

The recognition of specific characteristics among underlying conditions, such as neutropenia, solid organ transplantation, and surgical and nonsurgical critical illness, has enabled the description of distinct epidemiological patterns in the development of invasive candidiasis.

Conclusions

Despite its limited bedside practicality and before confirmation of potentially more accurate predictors, such as specific biomarkers, the CI remains an important way to characterize the dynamics of colonization, which increases early in patients who develop invasive candidiasis.

Molecular typing of Candida albicans isolates from hospitalized patients

SUMMARY

Introduction: The majority of nosocomial fungal infections are caused by Candida spp. where C. albicans is the species most commonly identified. Molecular methods are important tools for assessing the origin of the yeasts isolated in hospitals.

Methods: This is a study on the genetic profifiles of 39 nosocomial clinical isolates of C. albicans using two typing methods: random amplifified polymorphic DNA (RAPD) and microsatellite, two different primers for each technique were used.

Results: RAPD provided 10 and 11 different profiles with values for S_AB of 0.84 ± 0.126 and 0.88 ± 0.08 for primers M2 and P4, respectively. Microsatellite using two markers, CDC3 and HIS3, allowed the observation of six and seven different alleles, respectively, with combined discriminatory power of 0.91.

Conclusions: Although genetic variability is clear, it was possible to identify high similarity, suggesting a common origin for at least a part of isolates. It is important to emphasize that common origin was proven from yeasts isolated from colonization (urine, catheter or endotracheal secretions) and blood culture from the same patient, indicating that the candidemia must have started from a site of colonization. The combination of RAPD and microsatellite provides a quick and efficient analysis for investigation of similarity among nosocomial isolates of C. albicans.

Infection control in the intensive care unit

Nosocomial infections are common in many hospital departments, but particularly so on the intensive care unit, where they affect some 20 to 30% of patients. While early diagnosis and appropriate treatment are, of course, important, perhaps the greatest challenge is in the application of techniques to limit the development of such infections. This review will briefly discuss some of the background pathophysiology and epidemiology of nosocomial infection, and then focus on general and infection-specific preventative strategies individually and as part of broader infection-control programs with infection surveillance.

Possible transmission of Candida albicans on an intensive care unit: genotype and temporal cluster analyses

BACKGROUND

Nosocomial transmission of Candida spp. has not been fully explored and previous studies have shown conflicting results.

AIM

To evaluate the possible nosocomial transmission of Candida spp. on an intensive care unit (ICU).

METHODS

A prospective study was conducted for a period of 19 months, including all patients on our ICU with growth of Candida spp. from surveillance and directed cultures. Molecular typing with repetitive sequence-based polymerase chain reaction was used to define genotype relationships between the Candida albicans and Candida glabrata isolates. Candida isolates obtained from blood cultures taken from patients in our county outside the ICU were used as a reference. Temporal cluster analysis was performed to evaluate genotype distribution over time.

FINDINGS

Seventy-seven patients with 78 ICU stays, representing 12% of all ICU stays, were found to harbour 180 isolates of Candida spp. Molecular typing revealed 27 C. albicans genotypes and 10 of C. glabrata. Possible clustering, indicated by overlapping stays of patients with indistinguishable candida genotypes, was observed on seven occasions with C. albicans and on two occasions with C. glabrata. Two C. albicans genotypes were found significantly more often in the ICU group compared with the reference group. Moreover, C. albicans genotypes isolated from more than one patient were significantly more often found in the ICU group. Temporal cluster analysis revealed a significantly increased number of pairs with indistinguishable genotypes at a 21-day interval, indicating clustering.

CONCLUSION

This study indicates possible transmission of C. albicans between ICU patients based on genotyping and temporal cluster analysis.

The persistence of multifocal colonisation by a single ABC genotype of Candida albicans may predict the transition from commensalism to infection

Candida albicans is a common member of the human microbiota and may cause invasive disease in susceptible populations. Several risk factors have been proposed for candidaemia acquisition. Previous Candida multifocal colonisation among hospitalised patients may be crucial for the successful establishment of candidaemia. Nevertheless, it is still not clear whether the persistence or replacement of a single clone of C. albicans in multiple anatomical sites of the organism may represent an additional risk for candidaemia acquisition. Therefore, we prospectively evaluated the dynamics of the colonising strains of C. albicans for two groups of seven critically ill patients: group I included patients colonised by C. albicans in multiple sites who did not develop candidaemia and group II included patients who were colonised and who developed candidaemia. ABC and microsatellite genotyping of 51 strains of C. albicans revealed that patients who did not develop candidaemia were multiply colonised by at least two ABC genotypes of C. albicans, whereas candidaemic patients had highly related microsatellites and the same ABC genotype in colonising and bloodstream isolates that were probably present in different body sites before the onset of candidaemia.

Canadian clinical practice guidelines for invasive candidiasis in adults

Candidemia and invasive candidiasis (C/IC) are life-threatening opportunistic infections that add excess morbidity, mortality and cost to the management of patients with a range of potentially curable underlying conditions. The Association of Medical Microbiology and Infectious Disease Canada developed evidence-based guidelines for the approach to the diagnosis and management of these infections in the ever-increasing population of at-risk adult patients in the health care system. Over the past few years, a new and broader understanding of the epidemiology and pathogenesis of C/IC has emerged and has been coupled with the availability of new antifungal agents and defined strategies for targeting groups at risk including, but not limited to, acute leukemia patients, hematopoietic stem cell transplants and solid organ transplants, and critical care unit patients. Accordingly, these guidelines have focused on patients at risk for C/IC, and on approaches of prevention, early therapy for suspected but unproven infection, and targeted therapy for probable and proven infection.

Investigation of a cluster of Candida albicans invasive Candidiasis in a neonatal intensive care unit by pulsed-field gel electrophoresis

Nosocomial invasive candidiasis (IC) has emerged as a major problem in neonatal intensive care units (NICUs). We investigated herein the temporal clustering of six cases of neonatal IC due to Candida albicans in an NICU. Eighteen isolates obtained from the six neonates and two isolates from two health care workers (HCWs) working at the same unit and suffering from fingers' onychomycosis were genotyped by electrophoretic karyotyping (EK) and restriction endonuclease analysis of genomic DNA by using Sfi I (PFGE-Sfi I). PFGE-Sfi I was more effective in discriminating between temporally related isolates. It showed that (i) both HCWs had specific strains excluding them as a source of infections in neonates. (ii) Isolates collected from three neonates were identical providing evidence of their clonal origin and the occurrence of a horizontal transmission of C. albicans in the unit. (iii) The three remaining neonates had specific strains confirming that the IC cases were coincidental. (iv) Microevolution occurred in one catheter-related candidemia case. Our results illustrate the relevance of the molecular approach to investigate suspected outbreaks in hospital surveys and the effectiveness of PFGE-Sfi I for typing of epidemiologically related C. albicans isolates.

Temporal similarity between Candida albicans genotypes in a Tunisian neonatal intensive care unit suggests several nosocomial cross-contamination episodes

The nosocomial transmission of Candida albicans in neonatal intensive care units (NICUs) is an increasing concern and understanding the route of this transmission is critical for adequate infection control measures. The aim of our study was to assess the likeliness of nosocomial acquisition of C. albicans in the NICU of Farhat Hached hospital in Sousse (Tunisia). We genotyped 82 isolates from 40 neonates and 7 isolates from 5 health care workers (HCWs) with onychomycosis, by using CDC3 microsatellite length polymorphism (MLP) and the high-resolution melting (HRM) analysis. Combined MLP and HRM CD3 analysis led to the delineation of 12 genotypes. Five temporal clustering caused by five genotypes occurred during the study period. Three of these genotypes were isolated in both neonates and HCWs. The first clustering included 28 isolates obtained between January 2003 and May 2004 from 16 neonates and 2 HCWs. The second clustering included three isolates collected in 2004 from three neonates and two HCWs. The third clustering included 11 isolates obtained from 6 neonates and 1 HCW in 2006. The two remaining clustering could not be associated with any HCW's contamination. These results argue for the nosocomial transmission of C. albicans in our NICU. The combined MLP and HRM analysis is a rapid first approach for tracking cross-contamination.

Candida albicans strain-dependent modulation of pro-inflammatory cytokine release by in vitro oral and vaginal mucosal models

Candida albicans is a commensal organism at several sites and is a versatile, opportunistic pathogen. The underlying factors of pathogen and host associated with commensalism and pathogenicity in C. albicans are complex and their importance is largely unknown. We aimed to study the responses of oral epithelial (OEM) and vaginal epithelial models (VEM) to infection by oral and vaginal C. albicans strains to obtain evidence of inter-strain differences in pathogenicity and of site-specificity. Following inoculation of models, proinflammatory cytokines IL-1α, IL-1β, IL-6, IL-8 and prostaglandin E2 (PGE2) release were monitored and histological staining undertaken. Striking differences in strain behaviour and epithelial responses were observed. IL-1α, IL-1β and IL-8 release were significantly increased from the OEM in response to denture stomatitis strain NCYC 1467. Increased IL-8 release also followed infection of the OEM with both vaginal strains. Overall the VEM was relatively unresponsive to infection with either oral or vaginal strains under these conditions. Adherence and hyphal development were observed for all strains on both models although extensive, uniform tissue penetration was seen only with stomatitis strain NCYC 1467 on the OEM. Candidal strains were assayed for phospholipase (PL) and secreted aspartyl proteinase (SAP) activities where phospholipase (PL) activity was highest for strain NCYC 1467 although highest SAP activity was observed for vaginal strain NCPF 8112 in this assay. This is the first study to concurrently investigate cytokine production from oral and epithelial models using candidal strains originating from these respective mucosal sites from healthy and disease states. These data demonstrate significant differences in inflammatory responses of host epithelia to individual C. albicans strains.

Molecular typing of Candida albicans isolates from patients and health care workers in a neonatal intensive care unit

AIMS

The aim of this study was to investigate the genetic relatedness between Candida albicans isolates and to assess their nosocomial origin and the likeliness of cross-transmission between health care workers (HCWs) and hospitalized neonates in a neonatal intensive care unit (NICU).

METHODS

We retrospectively analysed 82 isolates obtained from 40 neonates and seven isolates from onychomycosis of the fingers of five HCWs in a Tunisian NICU by using pulsed-field gel electrophoresis (PFGE) and randomly amplified polymorphic DNA (RAPD) analysis with CA1 and CA2 as primers.

RESULTS

In RAPD analysis, the discriminatory power (DP) of CA1 and CA2 primers was 0·86 and 0·81, respectively. A higher DP was achieved by combining patterns generated by both primers (0·92), while PFGE karyotyping exhibited the lowest DP (0·62). The RAPD-CA1/CA2 analysis revealed that 65·8% of isolates obtained from neonates derived from a limited number (6) of groups of genetically identical strains, that five temporal clusterings occurred during the study period and that three HCWs' isolates and 11 isolates obtained from six neonates were identical.

CONCLUSIONS

These findings argue for the nosocomial transmission of C. albicans in our NICU and for the transfer of strains from HCWs to patients.

SIGNIFICANCE AND IMPACT OF THE STUDY

Identification of relatedness between Candida species obtained from neonates and health care workers by using molecular techniques with high discriminatory power is essential for setting up specific control measures in order to reduce the incidence of nosocomial candidiasis.

Multilocus sequence typing for Candida albicans isolates from candidemic patients: comparison with Southern blot hybridization and pulsed-field gel electrophoresis analysis

Background

We evaluated the efficacy of multilocus sequence typing (MLST) for assessing the genetic relationship among Candida albicans isolates from patients with candidemia in a hospital setting.

Methods

A total of 45 C. albicans isolates from 21 patients with candidemia were analyzed. The MLST results were compared with results obtained by Southern blot hybridization (C1 fingerprinting) and pulsed-field gel electrophoresis (PFGE). PFGE analysis included karyotyping and restriction endonuclease analysis of genomic DNAs using BssHII (REAG-B) and SfiI (REAG-S).

Results

The 45 isolates yielded 20 unique diploid sequence types (DSTs) by MLST, as well as 12 karyotypes, 15 REAG-B patterns, 13 REAG-S patterns, and 14 C1 fingerprinting types. Microevolution among intra-individual isolates was detected in 6, 5, 3, 5, and 7 sets of isolates by MLST (1 or 2 allelic differences), REAG-B, REAG-S, C1 fingerprinting, and a combination of all methods, respectively. Among 20 DSTs, 17 were unique, and 3 were found in more than 1 patient. The results of 2 DSTs obtained from 9 patient isolates were in agreement with REAG and C1 fingerprinting patterns. However, the remaining DST, which was shared by 2 patient isolates, showed 2 different PFGE and C1 fingerprinting patterns. In addition, 3 sets of isolates from different patients, which differed in only 1 or 2 alleles by MLST, also exhibited different PFGE or C1 fingerprinting patterns.

Conclusions

MLST is highly discriminating among C. albicans isolates, but it may have some limitations in typing isolates from different patients, which may necessitate additional analysis using other techniques.

Increased mortality in young candidemia patients associated with presence of a Candida albicans general-purpose genotype

The yeast Candida albicans causes life-threatening candidemia. A general-purpose genotype (GPG; corresponds to clade 1) causes more infections than other C. albicans genotypes. To investigate if GPG strains also cause higher mortality, we developed a duplex PCR assay which was 98% accurate in identifying GPG strains in an international collection of strains typed with probe Ca3. We applied the assay to 635 European C. albicans candidemia isolates. Of these, 18% conformed to the GPG genotype, 4% were of a borderline genotype, and 78% were of a non-GPG genotype, broadly consistent with genotype distributions in earlier studies. The prevalence of GPG strains was increased in females and in younger patients, exceeding 40% in infants aged ≤1 year. Logistic regression confirmed sex and age as significant determinants of GPG prevalence. Across the entire patient cohort, there was no difference in mortality for patients infected with GPG strains or other strains (36% versus 37%). However, mortality in patients aged ≤48 years was 33% for infection with GPG strains but only 15% for infection with other strains (z test; P < 0.01). Mortality rates associated with GPG and non-GPG strains were comparable in older patients (39% versus 46%). A logistic regression analysis confirmed the age-dependent impact of genotype on mortality. Thus, GPG strains may be more virulent than other strains in younger patients. Because candidemia is usually caused by endogenous strains, our PCR assay could potentially be used as a risk assessment tool for identifying younger patients most at risk of death from candidemia.

Prevalent nosocomial clusters among causative agents for candidemia in Hamilton, Canada

In Canada, the incidence of candidemia, the bloodstream infection caused by Candida species, varied from 1.2-5.1 cases/100,000, representing the third most common type of bloodstream infections in intensive care unit patients. However, the relative contributions of nosocomial transmission in candidemia remain poorly understood. In this study, we investigated the prevalence of nosocomial clusters among the causative agents for candidemia in Hamilton, Ontario, Canada, during a period from January 2005 to February 2009. We genotyped 134 isolates from 125 unrelated patients with candidemia, among which were 87 C. albicans, 20 C. parapsilosis, 11 C. glabrata, 15 C. tropicalis, and one C. krusei. Our PCR fingerprinting analyses using three highly polymorphic primers identified a total of 99 genotypes, with 18 of them shared by 44 independent isolates. Nine pairs of isolates were obtained from the same patients at the same time and each pair had identical fingerprints. Interestingly, all 44 independent strains belonging to each of the shared genotypes were isolated from patients within 3-months stay in the Hamilton hospitals. Both inter- and intra-ward clusters were found, including one that contained strains from intensive care units in two hospitals. Our results indicated that 33% of the patients with candidemia were infected by nosocomial clusters and suggested that measures should be taken in hospitals to prevent nosocomial acquisition of Candida infections.

Genomic plasticity of the human fungal pathogen Candida albicans

The genomic plasticity of Candida albicans, a commensal and common opportunistic fungal pathogen, continues to reveal unexpected surprises. Once thought to be asexual, we now know that the organism can generate genetic diversity through several mechanisms, including mating between cells of the opposite or of the same mating type and by a parasexual reduction in chromosome number that can be accompanied by recombination events (2, 12, 14, 53, 77, 115). In addition, dramatic genome changes can appear quite rapidly in mitotic cells propagated in vitro as well as in vivo. The detection of aneuploidy in other fungal pathogens isolated directly from patients (145) and from environmental samples (71) suggests that variations in chromosome organization and copy number are a common mechanism used by pathogenic fungi to rapidly generate diversity in response to stressful growth conditions, including, but not limited to, antifungal drug exposure. Since cancer cells often become polyploid and/or aneuploid, some of the lessons learned from studies of genome plasticity in C. albicans may provide important insights into how these processes occur in higher-eukaryotic cells exposed to stresses such as anticancer drugs.

Epidemiology of invasive mycoses in North America

The incidence of invasive mycoses is increasing, especially among patients who are immunocompromised or hospitalized with serious underlying diseases. Such infections may be broken into two broad categories: opportunistic and endemic. The most important agents of the opportunistic mycoses are Candida spp., Cryptococcus neoformans, Pneumocystis jirovecii, and Aspergillus spp. (although the list of potential pathogens is ever expanding); while the most commonly encountered endemic mycoses are due to Histoplasma capsulatum, Coccidioides immitis/posadasii, and Blastomyces dermatitidis. This review discusses the epidemiologic profiles of these invasive mycoses in North America, as well as risk factors for infection, and the pathogens' antifungal susceptibility.

Molecular phylogenetics and epidemiology of Candida albicans

Candida albicans, a diploid yeast commensal and opportunist pathogen, has evolved unusual mechanisms for maintenance of genetic diversity in the absence of a complete sexual cycle. These include chromosomal polymorphisms, mitotic recombination events, and gains and losses of heterozygosity, superimposed on a fundamentally clonal mode of reproduction. Molecular typing of C. albicans strains shows geographical evolutionary associations but these have become partially blurred, probably as a result of extensive human travel. Individual patients usually carry a single C. albicans strain type, but this may undergo microvariation leading to detection of mixtures of closely related types. Associations have been found between clade 1, the most common multilocus sequence typing cluster of related C. albicans strains, and resistance to flucytosine and terbinafine. There are also clade-related associations with lengths of tandem repeats in some cell-surface proteins, but not with virulence or type of infection.

Colony morphologies, species, and biotypes of yeasts from thrush and denture stomatitis

OBJECTIVE

To study the species and phenotypic characteristics of yeasts, i.e. colony morphology, biotypes, and biotype relatedness, and the oral distribution of yeasts, in thrush and denture stomatitis.

MATERIAL AND METHODS

Yeast colony morphology was observed under a stereo-microscope and photographed with a digital camera. Genus, species, and biotypes of the yeast isolates were identified by using a commercial kit, ID 32C. Yeast biotype dendrograms were generated by Spotfire software and SPSS 15.0 for Windows.

RESULTS

Multiple colony morphologies were observed among the yeasts from both thrush and denture stomatitis. One genus, 6 species, and 21 biotypes were identified among the yeasts from thrush, while 2 genera, 7 species, and 20 biotypes were identified among the yeasts from denture stomatitis. Considerable similarities in predominant species, biotypes, and biotype clustering profiles were shown among the yeasts from thrush and denture stomatitis. However, Candida dubliniensis was identified exclusively in subgingival areas and biotype 7347340215 of C. albicans was identified more frequently in palate and sulci in thrush.

CONCLUSIONS

A diversity of species and phenotypes was found among the yeasts in thrush and denture stomatitis. Candidal commensals were predominant in thrush and denture stomatitis, but the observation of divergent Candida species and biotypes, constituting 23% of all the yeast isolates, should not be ignored.

Molecular epidemiology of candidemia: evidence of clusters of smoldering nosocomial infections

BACKGROUND

Invasive fungal infections pose a serious threat to hospitalized patients worldwide. In particular, the prevalence of clusters of nosocomial infection among patients with candidemia remains unknown. The aim of this study was to investigate the molecular epidemiology of candidemia in a nationwide setting in Iceland during a 16-year period.

METHODS

The genotypes of all available fungal bloodstream isolates during 1991-2006 (n = 219) were determined by polymerase chain reaction fingerprinting with use of 4 separate primers. Clusters were defined as isolation of > or =2 strains with genotypes that had > or =90% relatedness in the same hospital within a period of 90 days.

RESULTS

Candida albicans represented 61.6% of isolates, followed by Candida glabrata (13.7%), Candida tropicalis (9.1%), and Candida parapsilosis (8.7%). Polymerase chain reaction fingerprinting revealed 35 clones of C. albicans, 10 clones of C. glabrata, 7 clones of C. tropicalis, 4 clones of C. parapsilosis, and 5 clones of Candida dubliniensis. Overall, 18.7%-39.9% of all infections were part of nosocomial clusters, most commonly caused by C. albicans, C. parapsilosis, and C. tropicalis. Most clusters involved 2 cases and disproportionately affected patients in adult and neonatal intensive care units (P = .045). The 7-day (16%) and 30-day (32%) case-fatality rates among cluster-associated cases did not differ statistically significantly from those for sporadic nosocomial infections. None of the clusters were identified by the hospital surveillance team.

CONCLUSIONS

In an unselected patient population, as many as one-third of all cases of candidemia may be attributable to nosocomial clusters. The risk is dependent on hospital wards and patient populations; it is highest in intensive care units. Small clusters are not identified by routine hospital surveillance.

SSD1 is integral to host defense peptide resistance in Candida albicans

Candida albicans is usually a harmless human commensal. Because inflammatory responses are not normally induced by colonization, antimicrobial peptides are likely integral to first-line host defense against invasive candidiasis. Thus, C. albicans must have mechanisms to tolerate or circumvent molecular effectors of innate immunity and thereby colonize human tissues. Prior studies demonstrated that an antimicrobial peptide-resistant strain of C. albicans, 36082(R), is hypervirulent in animal models versus its susceptible counterpart (36082(S)). The current study aimed to identify a genetic basis for antimicrobial peptide resistance in C. albicans. Screening of a C. albicans genomic library identified SSD1 as capable of conferring peptide resistance to a susceptible surrogate, Saccharomyces cerevisiae. Sequencing confirmed that the predicted translation products of 36082(S) and 36082(R) SSD1 genes were identical. However, Northern analyses corroborated that SSD1 is expressed at higher levels in 36082(R) than in 36082(S). In isogenic backgrounds, ssd1Delta/ssd1Delta null mutants were significantly more susceptible to antimicrobial peptides than parental strains but had equivalent susceptibilities to nonpeptide stressors. Moreover, SSD1 complementation of ssd1Delta/ssd1Delta mutants restored parental antimicrobial peptide resistance phenotypes, and overexpression of SSD1 conferred enhanced peptide resistance. Consistent with these in vitro findings, ssd1 null mutants were significantly less virulent in a murine model of disseminated candidiasis than were their parental or complemented strains. Collectively, these results indicate that SSD1 is integral to C. albicans resistance to host defense peptides, a phenotype that appears to enhance the virulence of this organism in vivo.

Molecular epidemiology of Candida species isolated from clinical specimens of intensive care unit patients

Epidemiological analysis of nosocomial Candida infections has gained importance due to an increase in these infections during the recent years. This study investigated the prevalence of clinical infections of Candida in anesthesiology intensive care unit patients, and ascertains the level of genetic diversity in the Candida species. A total of 70 Candida isolates, consisting of 42 Candida albicans, 16 Candida glabrata and 12 Candida tropicalis strains isolated from various clinical sites of infection of anesthesiology intensive care unit patients, were analysed. The susceptibility of the isolates against amphotericin B and fluconazole was determined by microdilution method according to Clinical and Laboratory Standards Institute M27-A2 standards. The strains were typed by random amplified polymorphic DNA (RAPD)-PCR using OPE-03, OPE-18, RP4-2 and AP50-1 primers. In the patients with Candida infections, most isolates exhibited different RAPD patterns. Only three C. albicans pairs isolated within a short time period had the same RAPD pattern. Most of the Candida infections in the anesthesiology intensive care unit of our hospital seem to be caused by endogenous strains. Exogenous spread of C. albicans infections occurred less frequently.

Susceptibility of gnotobiotic transgenic mice (Tgepsilon26) with combined deficiencies in natural killer cells and T cells to wild-type and hyphal signalling-defective mutants of Candida albicans

Germfree transgenic epsilon 26 mice (Tgepsilon26), deficient in natural killer cells and T cells, were colonized (alimentary tract) with Candida albicans wild-type or each of two hyphal transcription factor signalling mutant strains (efg1/efg1, efg1/efg1 cph1/cph1). Each Candida strain colonized the alimentary tract, infected keratinized gastric tissues to a similar extent, and induced a granulocyte-dominated inflammatory response in infected tissues. Both wild-type and mutant strains formed hyphae in vivo and were able to elicit an increase in cytokine [tumour necrosis factor alpha, interleukin (IL)-10 and IL-12] and chemokine (KC and macrophage inflammatory protein-2] mRNAs in infected tissues; however, administration of the wild-type strain was lethal for the Tgepsilon26 mice, whereas the mice colonized with the mutant strains survived. Death of the Tgepsilon26-colonized mice appeared to be due to occlusive oesophageal candidiasis, and not to disseminated candidiasis of endogenous origin. In contrast, the mutant strains exhibited a significantly reduced capacity to infect (frequency and severity) oro-oesophageal (tongue and oesophagus) tissues. Therefore, the two hyphal signalling-defective mutants were less able to infect oro-oesophageal tissues and were non-lethal, but retained their ability to colonize the alimentary tract with yeast and hyphae, infect keratinized gastric tissues, and evoke an inflammatory response in orogastric tissues.

Multiple-locus variable-number tandem-repeat analysis for rapid typing of Candida glabrata

A multiple-locus variable-number tandem-repeat analysis (MLVA) using six microsatellite markers was assessed in 127 Candida glabrata isolates. Thirty-seven different genotypes, stable both in vitro and in vivo, were observed. The highest discriminatory power (D = 0.902) was reached by using only four markers. MLVA seems to be relevant for C. glabrata typing.

A cluster of Candida krusei infections in a haematological unit

BACKGROUND

Candida krusei infections are associated with high mortality. In order to explore ways to prevent these infections, we investigated potential routes for nosocomial spread and possible clonality of C. krusei in a haematological unit which had experienced an unusually high incidence of cases.

METHODS

We searched for C. krusei contamination of the hospital environment and determined the level of colonization in patients and health care workers. We also analyzed the possible association between exposure to prophylactic antifungals or chemotherapeutic agents and occurrence of C. krusei. The C. krusei isolates found were genotyped by pulsed-field electrophoresis method in order to determine possible relatedness of the cases.

RESULTS

Twelve patients with invasive C. krusei infection and ten patients with potentially significant infection or mucosal colonization were documented within nine months. We were unable to identify any exogenic source of infection or colonization. Genetic analysis of the isolates showed little evidence of clonal transmission of C. krusei strains between the patients. Instead, each patient was colonized or infected by several different closely related genotypes. No association between medications and occurrence of C. krusei was found.

CONCLUSION

Little evidence of nosocomial spread of a single C. krusei clone was found. The outbreak may have been controlled by cessation of prophylactic antifungals and by intensifying infection control measures, e.g. hand hygiene and cohorting of the patients, although no clear association with these factors was demonstrated.

[Prevention of invasive candidiasis in the critically ill non neutropenic patient]

Prevention of invasive candidiasis (IC) in the setting of critically ill non neutropenic patients should be based on evidenced-based recommendations, namely improved hand hygiene, optimal catheter care, and rational and reduced use of broad-spectrum antibiotics. Concomitant interventions aimed at reducing risk factors are important to decrease IC.

Nosocomial candiduria in women undergoing urinary catheterization. Clonal relationship betweenstrains isolated from vaginal tract and urine

We determined the incidence of nosocomial candiduria associated with indwelling urinary catheters in 42 women with and without Candida spp. vaginal colonization being treated in the intensive care unit (ICU). We established a relationship between strains initially isolated from the vaginal tract and those subsequently recovered from urine samples through the use of random amplified polymorphic DNA (RAPD). The overall incidence of nosocomial candiduria in these patients was 21.4%. Vaginal colonization by Candida spp. was detected in 11 patients (26.2%) of whom 6 (54.5%) developed candiduria. In comparison, only 3 (9.7%) cases of candiduria were found in women who were not colonized by the yeast (RR: 4.4, 95% CI 1.61-86.8, P=0.005). The dendrogram obtained by RAPD using 14 primers showed that the strains isolated from vagina and urine samples in five women had high similarity values (SAB >0.9) forming independent clusters. Our study suggests that women vaginally colonized by Candida spp. in an ICU setting have a high risk of acquiring nosocomial candiduria and that strains isolated from both sites in a single patient may be genetically related.

Nosocomial fungal infections: epidemiology, diagnosis, and treatment

Invasive fungal infections are increasingly common in the nosocomial setting. Furthermore, because risk factors for these infections continue to increase in frequency, it is likely that nosocomial fungal infections will continue to increase in frequency in the coming decades. The predominant nosocomial fungal pathogens include Candida spp., Aspergillus spp., Mucorales, Fusarium spp., and other molds, including Scedosporium spp. These infections are difficult to diagnose and cause high morbidity and mortality despite antifungal therapy. Early initiation of effective antifungal therapy and reversal of underlying host defects remain the cornerstones of treatment for nosocomial fungal infections. In recent years, new antifungal agents have become available, resulting in a change in standard of care for many of these infections. Nevertheless, the mortality of nosocomial fungal infections remains high, and new therapeutic and preventative strategies are needed.

Epidemiology of Candidemia in a Turkish tertiary care hospital

In order to determine the local epidemiology of candidemia, Candida strains isolated between 1994 and 2000 were identified to species level; antifungal resistance patterns and DNA fingerprints were analyzed. Identification of Candida strains (n: 140) was performed with germ tube test and carbohydrate assimilation reactions. Minimal inhibitory concentrations were determined using a commercial test for 5-flucytosine and the broth macrodilution method according to NCCLS for fluconazole and amphotericin B. Molecular relatedness was determined by restriction endonuclease analysis of genomic DNA followed by probe hybridization. C. albicans (37.2%), C. parapsilosis (32.2%), and C. tropicalis (12.2%) comprised 114 (81.4%) of 140 isolates. Susceptibility tests did not reveal resistance to amphotericin B in any of the Candida isolates. Fluconazole resistance was detected in one isolate of C. krusei, and 5-flucytosine resistance in two C. tropicalis isolates and one C. albicans isolate. Significantly higher frequency of clusters with identical strains in C. parapsilosis and C. tropicalis was detected compared to C. albicans. Pediatric wards are particularly important in the nosocomial transmission of non-albicans candida species.

Multilocus sequence typing reveals intrafamilial transmission and microevolutions of Candida albicans isolates from the human digestive tract

Candida albicans is a human commensal that is also responsible for superficial and systemic infections. Little is known about the carriage of C. albicans in the digestive tract and the genome dynamics that occur during commensalisms of this diploid species. The aim of this study was to evaluate the prevalence, diversity, and genetic relationships among C. albicans isolates recovered during natural colonization of the digestive tract of humans, with emphasis on Crohn's disease patients who produce anti-yeast antibodies and may have altered Candida sp. carriage. Candida sp. isolates were recovered from 234 subjects within 25 families with multiple cases of Crohn's disease and 10 control families, sampled at the oral and fecal sites. Prevalences of Candida sp. and C. albicans carriage were 53.4% and 46.5%, respectively, indicating frequent commensal carriage. No differences in prevalence of carriage could be observed between Crohn's disease patients and healthy subjects. Multilocus sequence typing (MLST) of C. albicans isolates revealed frequent colonization of a subject or several members of the same family by genetically indistinguishable or genetically close isolates. These latter isolates differed by loss-of-heterozygosity events at one or several of the MLST loci. These loss-of-heterozygosity events could be due to either chromosome loss followed by duplication or large mitotic recombination events between complementary chromosomes. This study was the first to jointly assess commensal carriage of C. albicans, intrafamilial transmission, and microevolution. The high frequency of each of these events suggests that the digestive tract provides an important and natural niche for microevolutions of diploid C. albicans through the loss of heterozygosity.

Molecular subtyping of clinical isolates of Candida albicans and identification of Candida dubliniensis Malaysia

The genotypes of 221 recent isolates of Candida albicans from various clinical specimens of 213 patients admitted to the University Malaya Medical Centre, Malaysia was determined based on the amplification of a transposable intron region in the 25 S rRNA gene. The analyses of 178 C. albicans isolated from nonsterile clinical specimens showed that they could be classified into three genotypes: genotype A (138 isolates), genotype B (38 isolates) and genotype C (2 isolates). The genotyping of 43 clinical isolates from sterile specimens showed that they belonged to genotype A (29 isolates), genotype B (10 isolates), genotype C (2 isolates) and genotype D (2 isolates). The overall distribution of C. albicans genotypes in sterile and nonsterile specimens appeared similar, with genotype A being the most predominant type. This study reported the identification of C. dubliniensis (genotype D) in 2 HIV-negative patients with systemic candidiasis, which were missed by the routine mycological procedure. The study demonstrated the genetic diversity of clinical isolates of C. albicans in Malaysia.