Abstract
BackgroundCandida species are the most frequently found fungal pathogens causing nosocomial disease in a hospital setting. Such species must be correctly identified to ensure that appropriate control measures are taken and that suitable treatment is given for each species. Candida albicans is causing most fungal disease burden worldwide; the challenge lies in differentiating it from emerging atypical, minor and related species such as Candida dubliniensis and Candida africana. The purpose of this study was to compare identification based on MALDI-TOF MS to standard identification systems using a set of nosocomial isolates.MethodsEleven nosocomial samples were collected from 6 third-level hospitals in Bogotá, Colombia. All the samples were identified by combining MALDI-TOF MS with morphological characters, carbohydrate assimilation and molecular markers (D1/D2 and HWP1).ResultsThe present work describes the first collection of atypical Colombian Candida clinical isolates; these were identified as Candida albicans/Candida africana by their MALDI-TOF MS profile. Phenotypical characteristics showed that they were unable to produce chlamydospores, assimilate trehalose, glucosamine, N- acetyl-glucosamine and barely grew at 42 °C, as would be expected for Candida africana. The molecular identification of the D1/D2 region of large subunit ribosomal RNA and HWP1 hyphal cell wall protein 1 sequences from these isolates was consistent with those for Candida albicans. The mass spectra obtained by MALDI-TOF MS were analysed by multi-dimensional scaling (MDS) and cluster analysis, differences being revealed between Candida albicans, Candida africana, Candida dubliniensis reference spectra and two clinical isolate groups which clustered according to the clinical setting, one of them being clearly related to C. albicans.ConclusionThis study highlights the importance of using MALDI-TOF MS in combination with morphology, substrate assimilation and molecular markers for characterising Candida albicans-related and atypical C. albicans species, thereby overcoming conventional identification methods. This is the first report of hospital-obtained isolates of this type in Colombia; the approach followed might be useful for gathering knowledge regarding local epidemiology which could, in turn, have an impact on clinical management. The findings highlight the complexity of distinguishing between typical and atypical Candida albicans isolates in hospitals.
Highlights
Candida species are the most frequently found fungal pathogens causing nosocomial disease in a hospital setting
A similar result has been described in a report of a clinical case in Italy where the amplification product obtained was equal in size to that found for the C. albicans reference strain, but different to that from C. dubliniensis, its closely-related species, even though other findings using conventional identification agreed with C. africana typing [31]
The samples analysed here were classified as C. albicans by the hyphal cell wall protein 1 (HWP1) molecular marker which is useful in differentiating between C. albicans-related and minor species
Summary
Candida species are the most frequently found fungal pathogens causing nosocomial disease in a hospital setting. Candida albicans is causing most fungal disease burden worldwide; the challenge lies in differentiating it from emerging atypical, minor and related species such as Candida dubliniensis and Candida africana. Candida albicans is the pathogenic fungus most commonly found in the general population; its ease of transmission in hospitals causes high comorbidity rates [1, 2] This species causes mucosal infections, mainly oropharyngeal candidiasis (OPC) and vulvovaginal candidiasis (VVC); the relevant nosocomial presentation is related to candidaemia and invasive candidiasis which is associated with high mortality rates (~49 %) in an ICU [3]. A lack of chlamydospore formation, an inability to assimilate trehalose or amino sugars and poor growth at 42 °C are the most useful traits for distinguishing C. africana from C. albicans and C. dubliniensis [5, 6, 10, 11]
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