A new plate medium for rapid presumptive identification and differentiation of Enterobacteriaceae

A new selective differential agar medium for rapid presumptive identification of Enterobacteriaceae from water and food samples is described (EMX ID agar). By a combination of fluorogenic and chromogenic substrates, the medium detects the presence of beta-D-glucuronidase, beta-D-galactosidase, beta-D-xylosidase, tryptophane deaminase and H2S; additionally, cytochrome-oxidase and indole production can be demonstrated. This medium provides an inexpensive means for simple and rapid presumptive identification of E. coli and coliforms and for the differentiation within the Klebsiella-Enterobacter and the Proteus-Providencia-Morganella group. Furthermore, it allows to distinguish between the H2S-positive Enterobacteriaceae Citrobacter freundii, Salmonella spp., S. arizonae, Edwardsiella, Proteus mirabilis, P. vulgaris and some oxidase-positive bacteria.