Use of cost effective and rapid molecular tools for identification of Candida species, opportunistic pathogens

What about Current Diversity of Mycolactone-Producing Mycobacteria? Implication for the Diagnosis and Treatment of Buruli Ulcer

The identification of an emerging pathogen in humans can remain difficult by conventional methods such as enrichment culture assays that remain highly selective, require appropriate medium and cannot avoid misidentifications, or serological tests that use surrogate antigens and are often hampered by the level of detectable antibodies. Although not originally designed for this purpose, the implementation of polymerase-chain-reaction (PCR) has resulted in an increasing number of diagnostic tests for many diseases. However, the design of specific molecular assays relies on the availability and reliability of published genetic sequences for the target pathogens as well as enough knowledge on the genetic diversity of species and/or variants giving rise to the same disease symptoms. Usually designed for clinical isolates, molecular tests are often not suitable for environmental samples in which the target DNA is mixed with a mixture of environmental DNA. A key challenge of such molecular assays is thus to ensure high specificity of the target genetic markers when focusing on clinical and environmental samples in order to follow the dynamics of disease transmission and emergence in humans. Here we focus on the Buruli ulcer (BU), a human necrotizing skin disease mainly affecting tropical and subtropical areas, commonly admitted to be caused by Mycobacterium ulcerans worldwide although other mycolactone-producing mycobacteria and even mycobacterium species were found associated with BU or BU-like cases. By revisiting the literature, we show that many studies have used non-specific molecular markers (IS2404, IS2606, KR-B) to identify M. ulcerans from clinical and environmental samples and propose that all mycolactone-producing mycobacteria should be definitively considered as variants from the same group rather than different species. Importantly, we provide evidence that the diversity of mycolactone-producing mycobacteria variants as well as mycobacterium species potentially involved in BU or BU-like skin ulcerations might have been underestimated. We also suggest that the specific variants/species involved in each BU or BU-like case should be carefully identified during the diagnosis phase, either via the key to genetic identification proposed here or by broader metabarcoding approaches, in order to guide the medical community in the choice for the most appropriate antibiotic therapy.

Differentiation of Candida albicans complex species isolated from invasive and non-invasive infections using HWP1 gene size polymorphism

Background and Purpose

Taxonomy of Candida is controversial and has changed due to the investigation of the novel species. Candida africana and Candida dubliniensis are new members of the C. albicans complex that are currently gaining both clinical and epidemiologic significance. This study aimed to report the prevalence of C. africana among the strains isolated from patients using hyphal wall protein 1 (HWP1) gene size polymorphism.

Materials and Methods

In total, 235 yeasts confirmed as C. albicans complex based on chromogenic media and internal transcribed spacers sequencing isolated from various clinical forms of invasive and non-invasive candidiasis mainly candidemia were re-identified using HWP1 gene polymorphisms. The HWP1-polymerase chain reaction amplicons were re-confirmed by sequencing and BLAST analysis.

Results

Based on the HWP1 gene size polymorphism, 223 strains were identified as C. albicans (94.89%) from which 7 isolates produced two DNA fragments (850 and 941 bp). The C. dubliniensis (n=4, 1.7%), C. africana (n=1, 0.42%), and mix of C. albicans and C. africana (n=7, 2.97%) were also identified.

Conclusion

It can be said that C. albicans remains the most common Candida species, while C. dubliniensis and C. africana are rarely found among the patient isolates. Due to limited information on the molecular epidemiology of this novel yeast, more studies using molecular methods are recommended.

Candida africana and Candida dubliniensis as causes of pediatric candiduria: A study using HWP1 gene size polymorphism

Background

Candida species cause a wide spectrum of disease entities. Candida africana and Candida dubliniensis-members of Candida albicans complex-are currently gaining both clinical and epidemiologic significance.

Materials and methods

Totally, 150 pediatric isolates that had previously been identified as C. albicans species complex based on a positive germ tube test were included. The isolates were cultured on CHROMagar Candida medium to ensure their purity and the results of germ tube test. For definitive speciation, PCR amplification and size polymorphism of the hyphal wall protein 1 (HWP1) gene was used. The results of HWP1-PCR were confirmed by sequencing the amplified fragments for randomly selected isolates of C. africana and C. dubliniensis.

Results

All 150 isolates included in this study were reconfirmed as C. albicans complex on chromogenic media. Based on the HWP1 gene size polymorphism, 141 (94%) isolates were identified as C. albicans, 2 (1.33%) as C. africana, and 1 (0.67%) as C. dubliniensis. The remaining 6 (4%) C. albicans complex isolates were a mix of C. albicans and C. africana. All isolates of C. africana and C. dubliniensis have been recovered from cases of candiduria.

Conclusion

C. africana, either alone or mixed with C. albicans, could be a cause of candiduria among pediatric patients and should not be ignored.

Current Aspects in the Biology, Pathogeny, and Treatment of Candida krusei, a Neglected Fungal Pathogen

Fungal infections represent a constant and growing menace to human health, because of the emergence of new species as causative agents of diseases and the increment of antifungal drug resistance. Candidiasis is one of the most common fungal infections in humans and is associated with a high mortality rate when the fungi infect deep-seated organs. Candida krusei belongs to the group of candidiasis etiological agents, and although it is not isolated as frequently as other Candida species, the infections caused by this organism are of special relevance in the clinical setting because of its intrinsic resistance to fluconazole. Here, we offer a thorough revision of the current literature dealing with this organism and the caused disease, focusing on its biological aspects, the host-fungus interaction, the diagnosis, and the infection treatment. Of particular relevance, we provide the most recent genomic information, including the gene prediction of some putative virulence factors, like proteases, adhesins, regulators of biofilm formation and dimorphism. Moreover, C. krusei veterinary aspects and the exploration of natural products with anti-C. krusei activity are also included.

Identification of Candida Species from Clinical Samples in a Honduran Tertiary Hospital

Candida species are one of the most important causes of human infections, especially in hospitals and among immunocompromised patients. The correct and rapid etiological identification of yeast infections is important to provide adequate therapy, reduce mortality, and control outbreaks. In this study, Candida species were identified in patients with suspected fungal infection, and phenotypic and genotypic identification methods were compared. A total of 167 axenic fungal cultures and 46 clinical samples were analyzed by HardyCHROM^®, MicroScan^®(Omron Microscan Systems Inc, Renton, WA, USA), and PCR-RFLP (Restriction Fragment Length Polymorphisms). The species of the C. albicans complex were the most frequent, followed by C. tropicalis and C. glabrata. Less common but clinically relevant species of Candida were also isolated. The comparison between the three methods was concordant, especially for the most common Candida species. Fungal DNA amplification was successful in all clinical samples.

Rapid and Accurate Identification of Candida albicans and Candida dubliniensis by Real-Time PCR and Melting Curve Analysis

OBJECTIVE

Candida albicans and Candida dubliniensis are germ tube-positive pathogenic yeast species. Accurate identification of these two species is warranted since C. albicans is a highly pathogenic species while C. dubliniensis exhibits increased adherence to buccal epithelial cells, reduced susceptibility to azoles and resistance to flucytosine. We have developed a duplex real-time PCR assay for rapid detection and differentiation between clinical C. albicans and C. dubliniensis isolates.

MATERIALS AND METHODS

A duplex real-time PCR assay was developed by using two species-specific primer pairs and SYBR Green dye to differentiate C. albicans and C. dubliniensis isolates via melting curve analysis of real-time PCR amplicons. Amplification products were also analyzed by agarose gel electrophoresis to confirm real-time PCR results.

RESULTS

Melting temperatures (Tm) for reference strains of C. albicans and C. dubliniensis were 86.55 and 82.75°C, respectively. No amplicon was obtained with DNA from reference strains of 8 other common Candida spp. When real-time PCR was applied on 226 clinical isolates previously identified by the Vitek 2 system and/or PCR sequencing of rDNA, Tm values for C. albicans (n = 113) and C. dubliniensis (n = 98) were 86.68 ± 0.529 and 82.616 ± 0.535°C, respectively. The results were confirmed by agarose gel electrophoresis. No amplicon was obtained from 15 isolates belonging to 9 other Candida spp.

CONCLUSIONS

The real-time PCR assay described here does not require prior identification of clinical yeast isolates as C. albicans/C. dubliniensis by germ tube formation and accurately reports results within 2 h. Detection of amplicons by agarose gel electrophoresis is also suitable for resource-poor settings devoid of real-time PCR facilities.