Diluent composition for use of API 20E in characterizing marine and estuarine bacteria

Nine chemically defined inoculation diluents, with compositions ranging from 0.85% NaCl to 35% marine salts, were used to evaluate the influence of diluent composition on the biochemical profiles of 30 marine and estuarine bacterial strains, including species of Vibrio, Aeromonas, Allomonas, and Photobacterium. Results demonstrated that a 20% marine salts diluent enabled the characterization of halophilic strains normally nonreactive by the API 20E system. Furthermore, the use of 20% marine salts showed that certain environmental isolates, identifiable as Vibrio parahaemolyticus by the recommended clinical inoculation procedure, were Vibrio vulnificus. An analysis of the profiles provided by the nine diluents indicates that the API 20E system, modified by the use of a diluent composed of 20% marine salts and incubated at 22 degrees C, can provide a reliable tool for the rapid characterization of marine and estuarine bacterial isolates.