Isolation of Vibrio parahaemolyticus from fecal specimens on mannitol salt agar

Unless laboratories use an inhibitory medium, Vibrio parahaemolyticus will be unrecognizable in fecal specimens. The use of a medium exclusively for vibrio isolation, such as thiosulfate-citrate-bile salts-sucrose agar (TCBS), however, may not be considered economically justified in the United States. The isolation and recognition of V. parahaemolyticus is reported on mannitol salt agar (MS), a medium which is used for fecal specimens here. Eight Kanagawa-positive and two of three Kanagawa-negative strains of V. parahaemolyticus grew as well on MS as on TCBS and better than on a representative enteric medium, Hektoen enteric agar (HE). Twenty-two fecal specimens from 16 noninfected individuals were inoculated with known quantities of V. parahaemolyticus, and recovery of these vibrios was assessed on TCBS, MS, and HE. Recovery of vibrios from MS and TCBS was similar when inoculum size was 10(3) colony-forming units/ml or greater. Recovery of vibrios from mixed culture was distinctly lower on HE. The colonial morphology of V. parahaemolyticus and several other bacteria on MS is illustrated.