Comparison of pulsed-field gel electrophoresis with isoenzyme profiles as a typing system for candida tropicalis

Candida species are important nosocomial pathogens, particularly in immunocompromised and critically ill patients. A variety of methods have been used to differentiate strains, but an optimal system has not been established. We compared methods for typing a panel of nine related isolates of Candida tropicalis from an outbreak of sternal wound infections as well as four unrelated control isolates of this species. (The genetic relationships of the nine isolates in the panel had been confirmed previously by restriction fragment analysis.) Typing was undertaken without knowledge of an isolate's origin. Karyotyping by contour-clamped homogeneous electric field (CHEF) gel electrophoresis failed to distinguish between outbreak and control isolates. However, when chromosome-sized DNA was digested with SfiI, EagI, SacII, or NaeI and the fragments were separated by CHEF electrophoresis, the outbreak isolates were readily identified. The isoenzyme profiles of the outbreak isolates were identical and were distinctly different from those of the control isolates. While both isoenzyme profiles and the modified CHEF procedure were discriminatory, the latter is recommended as a relatively convenient and reproducible technique for comparison of types of C. tropicalis.