A selective medium (KS5) for the isolation of
Plesiomonas shigelloides and
Aeromonas hydrophila from fresh water fish and water samples was developed by modifying the Rimler-Shotts medium (RS). KS5 medium contains fructose and sucrose as fermentable carbohydrates, and penicillin G and oleandomycin phosphate as selective inhibitors. The mean recovery rates for
Plesiomonas and
Aeromonas strains on KS5 plates were 93 and 67%, respectively.
Plesiomonas strains formed whitish blue or blue colonies while
Aeromonas strains produced yellow or yellow orange colonies. On differentiation between
Plesiomonas and
Aeromonas isolated from fresh water environments, their morphology on KS5 plates were fully consistent with the characteristics of each genus including O/129 sensitivity, starch hydrolysis, and lysine and ornithine decarboxylation. Anaerobic culture was recommended for the selection of
Plesiomonas because some reference strains of
Pseudomonas could grow on KS5 plates under aerobic conditions. At the drainage outlet of tilapia culture ponds and within about 2km downstream,
Plesiomonas shigelloides was isolated on KS5 medium in relatively high densities.
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