Genotypic characterization of Listeria spp. isolated from fresh water fish

A total of 200 samples (muscles and viscera, 100 of each) of fresh water fish, walking catfish (Clarias batrachus) were screened for Listeria spp. All the samples were subjected to a two-step enrichment followed by plating on selective media. Confirmation of the isolates was on the basis of biochemical characters, haemolysis on blood agar and Christie, Atkins, Munch Petersen test. A total of 39 isolates of Listeria spp. were recovered. Of these 26 (67%), 8 (21%), 3 (8%) and 2 (5%) were Listeria monocytogenes, Listeria seeligeri, Listeria grayi and Listeria welshimeri, respectively. The isolates were subjected to a PCR assay for detection of the virulence-associated genes individually or together. The plcA, actA, hlyA and iap genes were detected in six strains, three genes (actA, hlyA and iap) in nine strains, the plcA, hlyA and iap in our strain, the hlyA and iap were in three strains, actA and hlyA in four strains, plcA and hlyA in our strain and hlyA in two strains. The hlyA and iap were also detected in L. seeligeri.