The molecular epidemiology of serial Candida tropicalis isolates from ICU patients as revealed by multilocus sequence typing and pulsed-field gel electrophoresis

The genetic profiles of 50 Candida tropicalis isolates serially collected from 14 patients during a prospective surveillance study in adult intensive care units (ICUs) were characterized by multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) of Nael restriction fragments. A total of 21 diploid sequence types (DSTs) and 43 genotypes were differentiated by MLST and PFGE, respectively. Significant correlations were found between PFGE genotypes and DST types (P < 0.05). Dendrogram5 generated by either MLST or PFGE-Nael showed that most isolates from the same patient co-clustered with high similarity regardless of the anatomical source of isolation. Maintenance, microvariation or replacement of C tropicalis isolates could be observed within the individual patients by further analysis of variations in MLST sequence data. Antifungal susceptibility testing revealed that 17 (34%) of 50 isolates presented high MICs to flucytosine (MIC >= 8 mu g/mL). Sixteen (94%) of these isolates belonged to DST 164, and these were collected from four patients with different PFGE genotypes. Isolates sharing the same DST may represent a common clone that underwent extensive mutation over time to cope with drug selection pressure, different hosts or different geographic environments. (C) 2009 Elsevier B.V. All rights reserved.