Media for isolation of Aeromonas spp. from faeces

Five solid media were evaluated for isolation of Aeromonas spp. from faeces: desoxycholate citrate agar (DCA), MacConkey's agar (MAC), xylose-desoxycholate-citrate agar (XDCA), Rogol's medium (ROG), which contained ampicillin 20 mg/L and p-nitrophenyl-glycerine 25 mg/L as inhibitors, and blood agar (BA) with ampicillin 10 mg/L. False negative oxidase tests limited the usefulness of DCA and MAC and, although the use of XDCA avoided the problem of fermentation of lactose, some Aeromonas spp. failed to grow on XDCA or produced minute colonies unsuitable for oxidase tests. BA yielded the highest rate of isolation for Aeromonas spp. from 323 faecal samples--15.2% for all Aeromonas spp. and 9.3% for enterotoxigenic (ENT+) strains. This compares with 10.8% for all strains and 6.5% for ENT+ strains isolated on DCA, 7.1% for all strains and 4% for ENT+ strains on MAC and 4% for all strains and 1.5% for ENT+ strains on ROG. Blood agar with ampicillin is recommended for isolation of Aeromonas spp. from faeces.