Oropharyngeal candidosis in AIDS patients: an epidemiological study using restriction analysis of Candida albicans total genomic DNA

Genotypic study of strains belonging to the genus Trichosporon

Trichosporon asahii is an opportunistic fungus considered the leading etiologic agent of trichospornosis, a disease that causes great morbidity/mortality among affected patients. The identification of the etiologic agent is generally obtained through physiological and morphological studies. Molecular investigations, such as species-specific primers (PCR), have recently been developed with the aim of applying a more simple, specific, and faster technology for mycological diagnosis. The genetic material amplification technique using ad-random primers (RAPD: random amplified polymorphic DNA) is an epidemiological tool which enables research on infection by and transmission of suspected agents. In this study, the amplified polymorphic DNA technique was used to determine the intraspecific diversity of 10 Trichosporon asahii strains. Primers OPAO-15 and 1821 were used and these allowed association to 5 and 3 electrophoretic patterns, respectively. The T. asahii molecular identification, which had been previously analyzed by conventional methods, was performed by means of primers TAAF and pITS4. Our results support the use of these techniques for clonality studies of the strains of this fungus as well as for the fast and specific identification of its members in clinical cases.

Multilocus sequence typing for analyses of clonality of Candida albicans strains in Taiwan

Multilocus sequence typing (MLST) was used to characterize the genetic profiles of 51 Candida albicans isolates collected from 12 hospitals in Taiwan. Among the 51 isolates, 16 were epidemiologically unrelated, 28 were isolates from 11 critically ill, human immunodeficiency virus (HIV)-negative patients, and 7 were long-term serial isolates from 3 HIV-positive patients. Internal regions of seven housekeeping genes were sequenced. A total of 83 polymorphic nucleotide sites were identified. Ten to 20 different genotypes were observed at the different loci, resulting, when combined, in 45 unique genotype combinations or diploid sequence types (DSTs). Thirty (36.1%) of the 83 individual changes were synonymous and 53 (63.9%) were nonsynonymous. Due to the diploid nature of C. albicans, MLST was more discriminatory than the pulsed-field gel electrophoresis-BssHII-restricted fragment method in discriminating epidemiologically related strains. MLST is able to trace the microevolution over time of C. albicans isolates in the same patient. All but one of the DSTs of our Taiwanese strain collections were novel to the internet C. albicans DST database (http://test1.mlst.net/). The DSTs of C. albicans in Taiwan were analyzed together with those of the reference strains and of the strains from the United Kingdom and United States by unweighted-pair group method using average linkages and minimum spanning tree. Our result showed that the DNA type of each isolate was patient specific and associated with ABC type and decade of isolation but not associated with mating type, anatomical source of isolation, hospital origin, or fluconazole resistance patterns.

Comparison of four molecular typing methods to assess genetic relatedness of Candida albicans clinical isolates in Taiwan

This report describes the investigation of the genetic profiles of 53 Candida albicans isolates collected from 18 hospitals in Taiwan using three PFGE-based typing methods (PFGE karyotyping, and PFGE of SfiI and BssHII restriction fragments) and one repetitive-sequence-PCR (rep-PCR) method. All four methods were able to identify clonal related isolates from the same patients. PFGE-BssHII exhibited the highest discriminatory power by discriminating 40 genotypes, followed by PFGE-SfiI (35 genotypes) and then by rep-PCR (31 genotypes), while PFGE karyotyping exhibited the lowest discriminatory power (19 genotypes). High discriminatory power can also be achieved by combining typing methods with different typing mechanisms, such as rep-PCR and PFGE-based typing methods. The results also showed that the genotype of each isolate was patient-specific and not associated with the source of the isolation, geographic origin or antifungal resistance.