Comparative Analysis of Simulated Candidemia Using Two Different Blood Culture Systems and the Rapid Identification of Candida albicans

Abstract

The goal of this study was to determine the time to detection of Candida species isolates using the two most commonly used automated blood culture systems, and to evaluate rapid, widely available methods for the presumptive identification of C. albicans. Candidemia models of eight commonly detected Candida species were prepared using ATCC standards. The times to detection were evaluated using the BACTEC 9240 (Becton Dickinson) and BacT/Alert 3D (bioMerieux) automated blood culture systems. The presence of pseudohyphae clusters was examined by Gram staining and wet preparation. Germ tube tests were performed directly from blood culture bottles. All samples were cultured on blood agar plates and macroscopically examined for the presence of an irregular margin (spiking). Most Candida species (618) except C. glabrata and C. krusei grew more rapidly in aerobic than in anaerobic conditions. Clusters of pseudohyphae were observed in cultures of C albicans and C. tropicalis. All culture bottles positive for C. albicans were positive by the germ tube test and macroscopically showed 'spiking.' Aerobic and anaerobic blood culture systems can effectively detect candidemia. Furthermore, the direct germ tube test may be the most useful available morphological presumptive identification method for C. albicans.