Evaluation of the Commercial Rapid Trehalose Test (GLABRATA RTT) for the Point of Isolation Identification of Candida glabrata Isolates in Primary Cultures

Abstract

Candidaemias account for 10-20% of nosocomial bloodstream infections depending on the study. Whilst Candida albicans remains the most frequently isolated species, Candida glabrata may be responsible for as many as 10-25% of all candidaemias. Moreover, C. glabrata is generally less susceptible to the azole antifungals than the majority of other pathogenic yeast species. Thus, a rapid test for the specific identification of isolates of C. glabrata would be useful for patient management if it could be performed at point of isolation, on primary cultures grown on standard mycological media directly from patient specimens. Under certain conditions, C. glabrata rapidly hydrolyses trehalose into glucose. The GLABRATA RTT kit allows detection of the preformed enzyme responsible for this action. This study has assessed GLABRATA RTT as an identification tool specifically at point of isolation. Sixty test isolates were evaluated: 39 clinical isolates of C. glabrata identified at the UK Mycology Reference Laboratory, examples of the recently described genetic relatives of C. glabrata, Candida nivariensis (n=6) and Candida bracarensis (n=1), and a selection of other common pathogenic yeast species (n=14). The test provided results within 30min. Although 77% (30/39) of confirmed C. glabrata isolates were correctly identified by GLABRATA RTT (positive trehalase test), 23% (9/39) of isolates gave negative or equivocal results. All other yeast species gave negative results. The performance of GLABRATA RTT in this study is compared to previous evaluations of the test which employed isolates pre-cultured on specialised media and to other existing conventional identification methodologies.