Trichosporon asahii causing nosocomial urinary tract infections in intensive care unit patients: genotypes, virulence factors and antifungal susceptibility testing

Trichosporon asahii is the causative agent of both superficial and deep-seated infections of increasing morbidity and mortality. Urinary tract infections (UTIs) due to T. asahii, frequently associated with indwelling medical devices, have been reported over the years. However, few studies have specifically focused on the genotypic diversity of T. asahii isolates from urine specimens from intensive care units (ICUs), let alone potential virulence factors and antifungal susceptibility testing. In the present study, 23 T. asahii isolates were collected from UTI patients in ICUs between January 2008 and January 2012. Three genotypes (I, III, IV) were determined based on the combination of internal transcribed spacer and intergenic spacer locus PCR. Protease, phospholipase and haemolysin production was assessed by halo formation on corresponding agar plates. Only haemolytic activity was observed to varying degrees. Neither protease nor phospholipase was detectable. Biofilm formation on polystyrene surfaces was detected through a formazan salt reduction assay. All clinical isolates had the ability to form biofilm. In contrast to the susceptibility of planktonic T. asahii cells to clinically used amphotericin B, 5-flucytosine, fluconazole, itraconazole and voriconazole, a remarkable rise in the MICs of these for biofilm T. asahii cells was observed. Our results suggested that genotype IV was the most prevalent genotype among T. asahii isolates from ICUs in China. Haemolysin and biofilm might contribute to the pathogenicity and recurrence of T. asahii-related UTIs. Although triazoles, especially voriconazole, were effective against planktonic T. asahii cells, they failed to treat preformed biofilms.