Genotypic heterogeneity and comparative pathogenicity of environmental isolates of Papiliotrema laurentii

Background: Papiliotrema laurentii is typically isolated from environmental sources but also occasionally from clinical specimens. Other close relatives may be misidentified as P. laurentii by phenotypic methods. P. laurentii strains usually lack melanin, however, one melanin-forming strain has also been isolated. Aim: To perform phenotypic and molecular identification and genotypic heterogeneity among environmental P. laurentii isolates and to study pathogenicity of melanin-forming and albino strain in normal and immunosuppressed mice. Methods: Eleven environmental isolates were subjected to phenotypic identification by Vitek2 and/or ID32C systems and molecular identification by PCR-sequencing of internal transcribed spacer (ITS) region and D1/D2 domains of rDNA. Genotypic heterogeneity was studied by sequence comparisons. Pathogenicity of melanized and albino P. laurentii strains was studied in intravenously infected normal and immunosuppressed BALB/c mice. Results: Of seven isolates with variable phenotypic identification results, four and five isolates exhibited >99% identity with P. laurentii for ITS region and D1/D2 domains of rDNA, respectively, and sequence comparisons identified four ITS haplotypes among P. laurentii isolates. Other isolates yielded expected results. Normal mice infected with 105 cells of melanized and non-melanized P. laurentii strains survived infection while infection of immunosuppressed mice with 107 cells resulted in mortality. Viable counts in brain and lung tissues were higher in mice infected with melanized than non-melanized strain and the organism persisted up to 14 days.