New selective plating medium for isolation of Vibrio vulnificus biogroup 1

Abstract

A new plating medium (VV agar) has been developed as an alternative to thiosulfate-citrate-bile salts-sucrose (TCBS) agar for the isolation of Vibrio vulnificus. Salicin (2% wt/vol) is employed as the source of carbohydrate, with potassium tellurite (0.0005% wt/vol), crystal violet (0.00015% wt/vol), oxgall (0.8% wt/vol), and a pH of 8.6 to inhibit growth of gram-positive and gram-negative organisms other than V. vulnificus. Because strains of V. vulnificus do not strongly ferment salicin in VV agar, a pH indicator has not been included in the medium. Growth of V. vulnificus appears on VV agar as large grey colonies with black centers. Other non-Vibrio strains which grow on the medium produce smaller colonies and fail to take up tellurite. VV agar has proved to be more effective than TCBS agar in inhibiting members of the Enterobacteriaceae as well as gram-positive cocci. Only Vibrio strains capable of utilizing salicin grow well on VV agar. Recovery and growth of V. vulnificus are superior on VV agar, compared with TCBS agar.