Analytical limits of three β-glucosidase-based commercial culture methods used in environmental microbiology, to detect enterococci

The enzyme-based test methods Enterolert, Chromocult Enterococci agar, and mEI agar, used to assess water quality through the detection Enterococcus spp., have been compared in terms of their analytical specificity and their ability to detect various enterococcal strains. To achieve this goal, we have tested 110 different non-enterococcal bacterial strains and 101 strains of Enterococcus spp. isolated from diverse origins. The results obtained showed that 69 (68.3%), 84 (83.2%), and 89 (88.1%) of the 101 enterococcal strains tested respectively yielded a positive signal with Enterolert, mEI, and Chromocult Enterococci. Regarding the specificity, none of the non-Enterococcus spp. strains tested were detectable by any of the three culture methods, except for Granulicatella adiacens which turned out positive on Chromocult Enterococci. The results of this study showed that, based on our collection of strains, the Enterolert test method detected less enterococcal strains than the two other methods.