Rapid Differentiation of Candida albicans from Non-albicans Species by Germ Tube Test Directly From Blood Culture Bottles

Abstract

Introduction: It is important to identify infection-causing yeasts rapidly and perform antifungal susceptibility tests in order to determine the treatment to be applied. The aim of this study was to use direct germ tube test (GTT) from blood culture bottle for rapid differentiation of albicans/non-albicans Candida species to evaluate the possble contribution of this test to the implementation of earlier and narrower-spectrum antifungal therapy compared to conventional methods. Materials and Methods: This 4-years retrospective study included 129 positive automated blood culture samples with yeast detected in Gram staining among 11,080 blood cultures obtained from inpatients in various wards. GTT was performed directly from these bottles. All isolates were identified by VITEK (bioMérieux, Marcy-l’Étoile, France) and antifungal susceptibility tests were performed with the VITEK 2® automated system (bioMérieux, Marcy-l’Étoile, France). Results: Candida albicans was identified as the causative agent in 57 (44.2%) of the 129 blood cultures with direct Gram staining from the bottle. Conventional GTT was positive for all C. albicans isolates (100%), while direct GTT from blood culture bottle was positive in 54 (94.73%). Direct GTT from blood culture yielded false-negative results in the remaining three samples (5.27%). There was 97.6% (126/129) agreement between conventional GTT method and direct GTT from blood culture bottle. Non-albicans Candida species were isolated from the 72 samples with negative direct GTT from blood culture bottle (43 C. parapsilosis, 17 C. tropicalis, 7 C. famata, 4 C. glabrata, and 1 C. lipolytica). Conventional GTT results were also negative for all of these isolates. Conclusion: Direct GTT from positive blood cultures that are shown to contain yeast by Gram staining enabled differentiation of albicans/nonalbicans Candida species one day earlier than conventional culture. This method shows a high agreement rate with conventional diagnostic tests. It should be kept in mind that false negative results may be obtained at very low rates. This test may be helpful for initiation of a more appropriate empirical antifungal treatment. Furthermore, it is easy and can be applied in all clinical microbiology laboratories.

Keywords

• diagnostic performance analysis
• blood stream infections
• candidemia yeasts
• identification