Multilocus sequence typing of sequentialCandida albicansisolates from patients with persistent or recurrent fungemia

ABC typing and extracellular enzyme production of Candida albicans isolated from Candida vulvovaginitis

BACKGROUND

Candida albicans is the most common and virulent genus Candida. Detection of virulence factors in this species plays an important role in the better understanding of pathogenesis and antifungal treatment. Molecular typing investigations are important in the epidemiological interpretation of infection. This study aimed to evaluate extracellular enzyme activity and genotyping of C. albicans species isolated from vulvovaginal samples.

METHODS

One hundred and three vaginal C. albicans isolates were tested for esterase, phospholipase, proteinase, and hemolysin activities by specific media. Besides, the DNA of C. albicans isolates was extracted and amplified for ABC genotyping.

RESULTS

The highest enzyme production of C. albicans isolates was for proteinase (97.1%) and esterase (95.2%), whereas 59.2% of C. albicans isolates were negative for hemolysin secretion. Genotype C (83.5%) was the most frequent genotype followed by genotype B (12.6%) and genotype A (3.9%).

CONCLUSION

It is concluded that genotype C was the predominant genotype in all examined vulvovaginal C. albicans isolates. Also, there was a significant difference between enzyme production in each genotype (except for proteinase).

The genotypes and virulence attributes of C. albicans isolates from oral leukoplakia

Background

There is a debate as to whether some types of oral leucoplakias (OL) are caused by Candida species, and whether they contribute to the malignant transformation, associated with a minority of such lesions. As no detailed population analysis of yeast isolates from OL is available, we evaluated the virulence attributes, and genotypes of 35 C. albicans from OL, and compared their genotypes with 18 oral isolates from healthy individuals.

Material and Methods

The virulence traits evaluated were esterase, phospholipase, proteinase, haemolysin and coagulase production, and phenotypic switching activity, and yeast adherence and biofilm formation. DNA from OL and control yeasts were evaluated for A, B or C genotype status.

Results

Phospholipase, proteinase, and coagulase activity and biofilm formation was observed in 80%, 66%, 97 % and 77 % of the isolates, respectively. Phenotypic switching was detected in 8.6%, while heamolytic, and esterase activity and adherence were noted in all isolates.

Conclusions

The genotype A was predominant amongst both the OL and control groups. Due to the small sample size of our study a larger investigation to define the role of candidal virulent attributes in the pathogenicity of OL is warranted, and the current data should serve as a basis until then.

Key words:C. albicans, oral cavity, leukoplakia, virulence factors, genotyping.

Molecular typing of multi-drug resistant Candida albicans isolated from the Segamat community, Malaysia

In the past decade, researchers have focused on the emergence of drug resistance in fungal pathogens such as Candida albicans, also considered as pathobionts that occur harmlessly in the human body but could potentially be triggered to cause diseases. The increasing rate of antifungal resistance in commensal gut fungi is alarming and should be further investigated. Here, we report seven novel MLST (Multi Locus Sequence Typing) genotypes of multi-drug resistant C. albicans isolates obtained from participants of a community study in Segamat, a district in the state of Johor, Malaysia. A total of eight C. albicans were isolated from four individuals, which were found to express high resistance against fluconazole, itraconazole, voriconazole and 5-fluorocytosine antifungals. MLST was performed to assess the clonal relatedness of these drug resistant isolates among themselves and against other strains isolated from other geographical regions. The novel MLST C. albicans sequence types suggest significant genetic changes compared to previous genotypes.

Genetic diversity assessed using PFGE, MLP and MLST in Candida spp. candidemia isolates obtained from a Brazilian hospital

Candida spp. are the main causative agents of invasive fungal infections in immunocompromised patients. Candidemia has attributable mortality rates of 15 to 35% and increases hospitalisation time and costs, thus making this disease a public health concern. This study aimed to use pulsed-field gel electrophoresis (PFGE), microsatellite length polymorphism (MLP) and multilocus sequence typing (MLST) to analyse the genetic relationships among 65 Candida spp. bloodstream isolates, including 35 Candida albicans, 15 Candida glabrata and 15 Candida tropicalis isolates, all of which were obtained from patients in a Brazilian hospital. Moreover, patient clinical data were assessed. All techniques resulted in high discriminatory indexes. C. albicans and C. tropicalis isolates showed high genetic variability, while C. glabrata isolates had relatively low genetic variability. Moreover, a cluster of C. glabrata isolates was identified in a hospital unit. New MLST sequence types, diploid sequence types and alleles are described. Relationships were not observed between the molecular typing results and clinical characteristics. The molecular typing of clinical strains increases our understanding of candidemia epidemiology and promotes the development of strategies that can reduce the incidence of this disease. Moreover, this study is the first to combine these techniques to genotype these three species in Brazil.

Characteristics of late recurrent candidemia in adult patients

BACKGROUND AND OBJECTIVES

Candida species are one of the most common causes of health care-associated bloodstream infections. However, recurrent candidemia is rare, and the characteristics of late recurrent (LR) candidemia are partly unclear. Our aim was to evaluate the characteristics of LR candidemia in adult patients.

PATIENTS AND METHODS

A retrospective cohort study was performed in the hospital district of Helsinki and Uusimaa in Finland (2007-2016). All candidemia cases were searched in an electronic database during the study period. Patients with LR candidemia were compared with patients with a single candidemia episode to evaluate the characteristics of LR candidemia. LR candidemia was defined as having at least two episodes of candidemia more than 30 days apart.

RESULTS

We identified 24 episodes of LR candidemia in 20 patients. Patients with LR candidemia represented 6% of all patients with candidemia during the study period, and most of these cases were nosocomial. The median time between the first and the recurrent episode was 5.1 months. One-year mortality in LR candidemia was 45%. Underlying gastrointestinal disease (OR 7.21, 95% CI 2.52-20.61) and history of intra-venous drug use (IVDU) (OR 3.62, 95% CI 1.03-12.69) were independent risk factors for LR candidemia in the multivariable analysis.

CONCLUSION

Our study indicates that the gastrointestinal tract may be a continuous source of infection in patients with chronic gastrointestinal diseases. Gastrointestinal diseases and IVDU should be regarded as risk factors for LR candidemia.

Genotyping of Candida albicans isolated from animals using 25S ribosomal DNA and ALT repeats polymorphism in repetitive sequence

Background and Purpose:

Candida albicans is the most prevalent Candida species isolated from animals. Candidiasis can be systemic in animals or may affect a single organ, such as the mouth, urinary tract, and skin. The aim of the present study was to determine the genetic diversity of C. albicans isolated from different animals and investigate the presence of a relationship between host specificity and genetic typing of C. albicans.

Materials and Methods:

For the purpose of the study, DNA extraction was performed on 27 clinical isolates of C. albicans obtained from animals. Subsequently, they were subjected to 25S ribosomal DNA amplification and ALT repeats in repetitive sequences (RPSs). The minimum inhibitory concentrations of fluconazole, ketoconazole, clotrimazole, nystatin, amphotericin B, and caspofungin were determined using the microdilution method based on the Clinical and Laboratory Standards Institute M27-S4 standard.

Results:

Out of 27 C. albicans strains, 11, 6, 5, and 5 cases were recognized as genotypes A (40.8%), E (22.2%), B (18.5%), and C (18.5%), respectively, through amplification using AS-I, which revealed 17 different types of C. albicans. By combining the two typing methods, 27 C. albicans strains were finally divided into 22 genotypes.

Conclusion:

Different genotypes showed genetic diversity among the C. albicans strains isolated from animal sources. The results revealed no special genotype relationship according to the host, anatomical source of isolation, and antifungal susceptibility.

Risk Factors and Outcomes of Recurrent Candidemia in Children: Relapse or Re-Infection?

In this paper, our aim was to investigate the incidence, clinical characteristics, risk factors, and outcomes of recurrent candidemia in children. We retrospectively reviewed all children with candidemia from a medical center in Taiwan between 2004 and 2015. Two episodes of candidemia ≥30 days apart with clinical and microbiological resolution in the interim were defined as "late recurrence", and those that had 8⁻29 days apart from previous episodes were defined as "early recurrence". 45 patients (17.2%) had 57 episodes of recurrent candidemia, and 24 had 28 episodes of late recurrent candidemia. The median time between recurrences was 1.8 months (range: <1 month to 13 months). Of those, 29 had relapsed candidemia and 28 were re-infected by different Candida species (n = 24) or by different strains (n = 4). Recurrent candidemia patients were more likely to require echinocandins treatment, had a longer duration of candidemia, and higher rate of treatment failure (p = 0.001, 0.014, and 0.012, respectively). Underlying gastrointestinal diseases (Odds ratio (OR) 3.84; 95% Confidence interval (CI) 1.81⁻8.12) and neurological sequelae (OR 2.32; 95% CI 1.15⁻4.69) were independently associated with the development of recurrent candidemia. 17.2% of pediatric patients with candidemia developed recurrent candidemia, and approximately half were re-infected. Underlying gastrointestinal diseases and neurological sequelae were the independent risk factors for recurrent candidemia.

Multilocus sequence typing of Candida albicans isolates from the oral cavities of patients undergoing haemodialysis

This study evaluates the prevalence, diversity, and genetic profiles of Candida albicans isolates recovered from the oral cavities of haemodialysis patients. Oral swab samples were obtained from haemodialysis patients (n = 126) and healthy control subjects (n = 233) and Candida species were characterised. There was no significant difference between the haemodialysis and control groups in the prevalence of yeast carriers (23.6% vs. 31.0%, respectively) or C. albicans carriers (19.8% vs. 21.0%, respectively). C. albicans was the most populous species in both cohorts, followed by C. parapsilosis. C. parapsilosis and C. glabrata were more prevalent in the haemodialysis group than in the control group (C. parapsilosis 5.6% vs. 0.9% and C. glabrata 3.2% vs. 0.4%, respectively; P < 0.05). C. albicans isolates were analysed by multilocus sequence typing and the results were used to construct a phylogenetic tree. Most haemodialysis isolates were placed into Clade 4 (20.0%) and Clade 19 (16.0%) and most control isolates into Clade 8 (17%) and Clade 4 (14.9%). Differences in the strain abundance in each clade were not statistically significant between the two groups. Moreover, there was no significant association between the health status or diagnosis and either the sequence types or clades.

Antifungal tolerance is a subpopulation effect distinct from resistance and is associated with persistent candidemia

Tolerance to antifungal drug concentrations above the minimal inhibitory concentration (MIC) is rarely quantified, and current clinical recommendations suggest it should be ignored. Here, we quantify antifungal tolerance in Candida albicans isolates as the fraction of growth above the MIC, and find that it is distinct from susceptibility/resistance. Instead, tolerance is due to the slow growth of subpopulations of cells that overcome drug stress more efficiently than the rest of the population, and correlates inversely with intracellular drug accumulation. Many adjuvant drugs used in combination with fluconazole, a widely used fungistatic drug, reduce tolerance without affecting resistance. Accordingly, in an invertebrate infection model, adjuvant combination therapy is more effective than fluconazole in treating infections with highly tolerant isolates and does not affect infections with low tolerance isolates. Furthermore, isolates recovered from immunocompetent patients with persistent candidemia display higher tolerance than isolates readily cleared by fluconazole. Thus, tolerance correlates with, and may help predict, patient responses to fluconazole therapy.

The authors show that antifungal tolerance, defined as the fraction of growth of a fungal pathogen above the minimal inhibitory concentration, is due to the slow growth of subpopulations of cells that overcome drug stress, and that high tolerance is often associated with persistent infections.

Genomic and Phenotypic Variation in Morphogenetic Networks of Two Candida albicans Isolates Subtends Their Different Pathogenic Potential

The transition from commensalism to pathogenicity of Candida albicans reflects both the host inability to mount specific immune responses and the microorganism’s dimorphic switch efficiency. In this study, we used whole genome sequencing and microarray analysis to investigate the genomic determinants of the phenotypic changes observed in two C. albicans clinical isolates (YL1 and YQ2). In vitro experiments employing epithelial, microglial, and peripheral blood mononuclear cells were thus used to evaluate C. albicans isolates interaction with first line host defenses, measuring adhesion, susceptibility to phagocytosis, and induction of secretory responses. Moreover, a murine model of peritoneal infection was used to compare the in vivo pathogenic potential of the two isolates. Genome sequence and gene expression analysis of C. albicans YL1 and YQ2 showed significant changes in cellular pathways involved in environmental stress response, adhesion, filamentous growth, invasiveness, and dimorphic transition. This was in accordance with the observed marked phenotypic differences in biofilm production, dimorphic switch efficiency, cell adhesion, invasion, and survival to phagocyte-mediated host defenses. The mutations in key regulators of the hyphal growth pathway in the more virulent strain corresponded to an overall greater number of budding yeast cells released. Compared to YQ2, YL1 consistently showed enhanced pathogenic potential, since in vitro, it was less susceptible to ingestion by phagocytic cells and more efficient in invading epithelial cells, while in vivo YL1 was more effective than YQ2 in recruiting inflammatory cells, eliciting IL-1β response and eluding phagocytic cells. Overall, these results indicate an unexpected isolate-specific variation in pathways important for host invasion and colonization, showing how the genetic background of C. albicans may greatly affect its behavior both in vitro and in vivo. Based on this approach, we propose that the co-occurrence of changes in sequence and expression in genes and pathways driving dimorphic transition and pathogenicity reflects a selective balance between traits favoring dissemination of the pathogen and traits involved in host defense evasion. This study highlights the importance of investigating strain-level, rather than species level, differences, when determining fungal–host interactions and defining commensal or pathogen behavior.

Investigating Clinical Issues by Genotyping of Medically Important Fungi: Why and How?

Genotyping studies of medically important fungi have addressed elucidation of outbreaks, nosocomial transmissions, infection routes, and genotype-phenotype correlations, of which secondary resistance has been most intensively investigated. Two methods have emerged because of their high discriminatory power and reproducibility: multilocus sequence typing (MLST) and microsatellite length polymorphism (MLP) using short tandem repeat (STR) markers. MLST relies on single-nucleotide polymorphisms within the coding regions of housekeeping genes. STR polymorphisms are based on the number of repeats of short DNA fragments, mostly outside coding regions, and thus are expected to be more polymorphic and more rapidly evolving than MLST markers. There is no consensus on a universal typing system. Either one or both of these approaches are now available for Candida spp., Aspergillus spp., Fusarium spp., Scedosporium spp., Cryptococcus neoformans, Pneumocystis jirovecii, and endemic mycoses. The choice of the method and the number of loci to be tested depend on the clinical question being addressed. Next-generation sequencing is becoming the most appropriate method for fungi with no MLP or MLST typing available. Whatever the molecular tool used, collection of clinical data (e.g., time of hospitalization and sharing of similar rooms) is mandatory for investigating outbreaks and nosocomial transmission.

Candida albicans isolates from a single hospital show low phenotypical specialization

Candida albicans is the best-studied opportunistic human pathogenic yeast species, and its virulence factors, susceptibility to antimycotics, the diversity of its physiological properties and the determinative factors of these traits are interesting from a clinical as well as from an evolutionary perspective. By applying statistical modeling for the phenotypical differences observed among a collection of 63 C. albicans isolates originating from different clinical care units, from a diverse group of patients with or without mycosis, collected in a Hungarian clinic, we found that (i) host-related aspects like anatomical source, care unit of isolation, patients' age, sex, and disease severity, or ABC genotypes of the isolates had less effect on the phenotypic features of this opportunistic pathogen than host-independent aspects, for example, year or month of isolation; (ii) different phenotypic traits did not show any significant correlations with each other; and (iii) different genotypes displayed no anatomical specialization and rarely showed any significant correlation with parameters of isolation either. These results shed light on the dynamic nature and low specialization of the C. albicans populations observable in a narrow geographic range, namely in the patients hospitalized in the different care units of the clinic.

Risk factors for late recurrent candidaemia. A retrospective matched case-control study

Incidence, risk factors and clinical significance of late recurrent (LR) candidaemia (>1 month between episodes) remains unclear. The 1219 episodes of candidaemia detected from January 1985 to December 2014 were reviewed. We selected all cases with more than one episode separated by at least 30 days after clinical resolution in the interim (cases) and compared each of them with two controls (patients with single episodes of candidaemia). Clinical strains were genotyped to differentiate relapses from re-infection. Eighteen patients (1.48%) had 36 episodes of LR candidaemia (median 4 months). Independent risk factors for recurrence in the multivariate analysis were: underlying gastrointestinal disease (OR 67.16; 95% CI 5.23-861.71; p 0.001) and fungaemia due to Candida parapsilosis (OR 9.10; 95% 1.33-62.00; p 0.02). All episodes of LR candidaemia diagnosed during the first 3 months were due to an intravascular source of infection, whereas in those occurring after 3 months the main source of the disease was the abdomen, followed by endocarditis, and urinary tract. Molecular typing showed that 42.9% of LR candidaemias were relapses and 57.1% were re-infections. Neither time of recurrence nor clinical origin could predict type of recurrence. LR candidaemia is a relatively rare event that is more frequent in patients who have an initial episode of candidaemia due to C. parapsilosis or an underlying gastrointestinal disease. Episodes of LR candidaemia that occur within the first 3 months should prompt an attempt to exclude an intravascular source of infection, whereas those occurring later point to an intra-abdominal origin.

Molecular surveillance of candidemia due to Candida albicans among cancer patients during 2009 to 2013 by microsatellite typing

BACKGROUND

Since the high morbidity and mortality of candidemia among cancer patients, the epidemiology has been underlined. In recent years, Candida species genotyping has been established, which could provide detail characteristics of epidemiology and has been underscored for candidemia preventing strategies.

METHODS

Data of cancer patients with candidemia and hospitalized in Tianjin Medical University Cancer Institute and Hospital (TMUCIH) during 2009-2013 were reviewed. Species identification was carried out by using VITEK-2 Compact. Microsatellite typing was performed for molecular analysis. SPSS 20.0 and MVSP 3.22 software were used for statistical and clustering analysis, respectively.

RESULTS

Total of 36 isolates of Candida albicans were recovered from 36 cancer patients with nosocomial candidemia in TMUCIH during the period of 2009-2013 included in the study. Total of 17 genotypes were identified and 2 of them were endemic genotypes, which caused 21 (58.3%) of 36 episodes of candidemia. Hepatobiliary oncology, ICU and gastrointestinal oncology were the main wards of infections due to endemic strains. Gastrointestinal cancer and insertion of a nasogastric tube were the predictors of infections caused by endemic strains (p = 0.014 and p = 0.041, respectively). For the 36 cases, crude mortality was up to 30.6%, and there was no significant difference between infections due to endemic and non-endemic strains (p = 0.077).

CONCLUSIONS

This study proved that endemic stains of C. albicans could exist for a long period and mainly in a few wards. Patients with gastrointestinal cancer or nasogastric tube insertion were more sensitive to endemic C. albicans.

Multilocus sequence typing of Candida albicans isolates from a burn intensive care unit in Iran

Burn intensive care unit (BICU) patients are specifically exposed to deep-seated nosocomial infections due to Candida albicans. Superficial carriage of C. albicans is a potential source of infection and dissemination, and typing methods could be useful to trace the different isolates. Multilocus sequence typing is a powerful genotyping method for pathogenic micro-organisms, including Candida albicans. Thirty clinical isolates of C. albicans obtained from 22 patients that were admitted to the BICU from a burn hospital at Sari, Mazandaran state, Iran, were studied epidemiologically by multilocus sequence typing (MLST). Seventy-five variable nucleotide sites were found. Sixty-two alleles were identified among the seven loci of the C. albicans isolates and one new allele was obtained. Eighteen diploid sequence types (DSTs) were identified, and among those 10 were new. These isolates belonged to nine clonal clusters (CCs) while two isolates occurred as singletons. Eleven (36.7 %) isolates belonged to CC 124 after eBURST analysis and 13 isolates (43.3 %) were assigned to clade 4. Approximately 17 % of the 30 isolates belonged to clade 1 (CC 69 and CC 766). Isolates from several patients with burns were found to be related genetically. Some patients yielded multiple isolates with identical DSTs, suggesting colonization or infection caused by cross-contamination between patients. Isolates that show identical or similar allelic profiles are presumed to be identical or closely related and may be used to evaluate the genetic relationships between isolates from a specific environment such as the BICU.

In vivo imaging of disseminated murine Candida albicans infection reveals unexpected host sites of fungal persistence during antifungal therapy

OBJECTIVES

Candida albicans is an important fungal pathogen that can cause life-threatening disseminated infections. To determine the efficacy of therapy in murine models, a determination of renal fungal burden as cfu is commonly used. However, this approach provides only a snapshot of the current situation in an individual animal and cryptic sites of infection may easily be missed. Thus, we aimed to develop real-time non-invasive imaging to monitor infection in vivo.

METHODS

Bioluminescent C. albicans reporter strains were developed based on a bioinformatical approach for codon optimization. The reporter strains were analysed in vitro and in vivo in the murine model of systemic candidiasis.

RESULTS

Reporter strains allowed the in vivo monitoring of infection and a determination of fungal burden, with a high correlation between bioluminescence and cfu count. We confirmed the kidney as the main target organ but additionally observed the translocation of C. albicans to the urinary bladder. The treatment of infected mice with caspofungin and fluconazole significantly improved the clinical outcome and clearance of C. albicans from the kidneys; however, unexpectedly, viable fungal cells persisted in the gall bladder. Fungi were secreted with bile and detected in the faeces, implicating the gall bladder as a reservoir for colonization by C. albicans after antifungal therapy. Bile extracts significantly decreased the susceptibility of C. albicans to various antifungals in vitro, thereby probably contributing to its persistence.

CONCLUSIONS

Using in vivo imaging, we identified cryptic sites of infection and persistence of C. albicans in the gall bladder during otherwise effective antifungal treatment. Bile appears to directly interfere with antifungal activity.

Candida species distribution, genotyping and virulence factors of Candida albicans isolated from the oral cavity of kidney transplant recipients of two geographic regions of Brazil

BACKGROUND

Candida albicans is a diploid yeast that in some circumstances may cause oral or oropharyngeal infections. This investigation aimed to study the prevalence of Candida spp. and to analyze the ABC genotypes of 76 clinical isolates of C. albicans obtained from the oral cavity of kidney transplant patients from two distinct geographic regions of Brazil.

METHODS

We typed 48 strains with ABC genotyping and Microsatelitte using primer M13 and tested three virulence factors in vitro: phospholipase activity, morphogenesis and the ability to evade from polymorphonuclear neutrophils phagocytosis.

RESULTS

C. albicans was the most prevalent species (86.4%), followed by C. tropicalis (4.5%). C. albicans genotype A was the most prevalent (58 isolates; 76.4%), followed by genotype C (15 isolates; 19.7%) and genotype B (3 isolates; 3.9%). When Microsatellite technique with primer M13 was applied, 80% of the isolates from the South were placed within the same cluster. The majority of Genotype C strains were grouped together within two different clusters. Genotype C was considered more resistant to PMNs attack than genotypes A and B. Strains isolated from the South of Brazil showed also better ability to combat PMNs phagocytosis.

CONCLUSIONS

We found a high rate of C. albicans genotype C strains isolated from the oral cavity of this group of patients. This study characterized oral C. albicans strains isolated from kidney transplant recipients and will contribute to a better understanding of the pathogenesis of oral candidiasis.

Molecular epidemiology, phylogeny and evolution of Candida albicans

A small number of Candida species form part of the normal microbial flora of mucosal surfaces in humans and may give rise to opportunistic infections when host defences are impaired. Candida albicans is by far the most prevalent commensal and pathogenic Candida species. Several different molecular typing approaches including multilocus sequence typing, multilocus microsatellite typing and DNA fingerprinting using C. albicans-specific repetitive sequence-containing DNA probes have yielded a wealth of information regarding the epidemiology and population structure of this species. Such studies revealed that the C. albicans population structure consists of multiple major and minor clades, some of which exhibit geographical or phenotypic enrichment and that C. albicans reproduction is predominantly clonal. Despite this, losses of heterozygosity by recombination, the existence of a parasexual cycle, toleration of a wide range of aneuploidies and the recent description of viable haploid strains have all demonstrated the extensive plasticity of the C. albicans genome. Recombination and gross chromosomal rearrangements are more common under stressful environmental conditions, and have played a significant role in the evolution of this opportunistic pathogen. Surprisingly, Candida dubliniensis, the closest relative of C. albicans exhibits more karyotype variability than C. albicans, but is significantly less adaptable to unfavourable environments. This disparity most likely reflects the evolutionary processes that occurred during or soon after the divergence of both species from their common ancestor. Whilst C. dubliniensis underwent significant gene loss and pseudogenisation, C. albicans expanded gene families considered to be important in virulence. It is likely that technological developments in whole genome sequencing and data analysis in coming years will facilitate its routine use for population structure, epidemiological investigations, and phylogenetic analyses of Candida species. These are likely to reveal more minor C. albicans clades and to enhance our understanding of the population biology of this versatile organism.

Analysis of strain relatedness using high resolution melting in a case of recurrent candiduria

BACKGROUND

Several genotyping protocols have been described to study Candida albicans strains with different sensitivity values. In this study we have analyzed the genetic relatedness and the antifungal susceptibility of several Candida albicans strains isolated from a patient who from suffered recurrent candiduria for a period of five years. Strains were genotyped using Microsatellite Length Polymorphism (MLP) with three microsatellite markers (HIS 3, EF 3 and CDC 3), and a new method based on high resolution melting (HRM) was developed to analyze the microsatellite region. This method was compared with the conventional technique that uses capillary electrophoresis.

RESULTS

MICs of the isolates showed the existence of fluconazole susceptible and resistant strains. An inter-colony test using single concentration (8 and 16 mg/l) of fluconazole revealed the coexistence of both fluconazole susceptible and resistant strains. Both genotyping analysis methods showed that all the patient's isolates had a clonal origin. HRM analysis method developed was able to accurately establish strain relatedness and presented a discriminatory power of 0.77.

CONCLUSIONS

Although HRM analysis method presented a lower discriminatory power compared to methods based on capillary electrophoresis, it provided a more cost-effective and suitable alternative for genotyping C. albicans in a clinical laboratory.

Multilocus sequence typing of Candida tropicalis shows the presence of different clonal clusters and fluconazole susceptibility profiles in sequential isolates from candidemia patients in Sao Paulo, Brazil

The profiles of 61 Candida tropicalis isolates from 43 patients (28 adults and 15 children) diagnosed with candidemia at two teaching hospitals in São Paulo, Brazil, were characterized by multilocus sequence typing (MLST). For the 14 patients who had bloodstream infections, 32 isolates were serially collected from their blood and/or catheters. Thirty-nine diploid sequence types (DSTs) were differentiated. According to the C. tropicalis MLST database (http://pubmlst.org/ctropicalis/), 36 DSTs and 23 genotypes identified from the 61 isolates had not previously been described. This report represents the first study to characterize sequential isolates of C. tropicalis from candidemia cases in South America. Microvariation in a single gene was found in the sequential isolates from 7 patients. The main polymorphisms occurred in the alleles of the XYR1 gene, specifically at nucleotide positions 215, 242, and 344. Macrovariation in six gene fragments was detected in the isolates from 3 patients. eBURST analysis added two new groups to this study (groups 6 and 18). Additionally, susceptibility tests indicate that 3 isolates were resistant to fluconazole. No correlation was found between the DSTs and susceptibility to fluconazole and/or selective antifungal pressure. Two patients were sequentially infected with resistant and susceptible strains. MLST is an important tool for studying the genetic diversity of multiple/sequential isolates of patients with candidemia, allowing the comparison of our data with those from other regions of the world, as well as allowing an analysis of the genetic relationship among several clones in sequential isolates from the same or different candidemia patient sites (blood or catheter).