Automated detection of amino acid decarboxylation in salmonellae and other Enterobacteriaceae

Amino acid decarboxylase (DC) activities ofSalmonellaspp. and other Enterobacteriaceae were studied using the BioSys, a novel automated system for detection of microbial metabolic activities. The growth media consisted of peptone, glucose and yeast extract, alone and supplemented with 0.5% (w/v)L-lysine,L-arginine orL-ornithine, and bromcresol purple as the pH dye indicator. Changes in the indicator color in response to acid (yellow), and amine production (reversal to purple), were monitored during incubation at 35°C. All 14 Salmonella strains tested had positive lysine, ornithine and arginine DC activity. Time for the shift in the indicator color to purple was consistently shortest in media containing ornithine, followed closely by lysine, and was longest in the presence of arginine. DC activity of 10 non-Salmonella Enterobacteriaceae depended on the strain and genus. Coupled with detection of other phenotypic reactions in the automated system, decarboxylation is useful for differentiation of salmonellae from other Enterobacteriaceae.