Incidence of Listeria spp. in tropical fish

The incidence of Listeria spp. in tropical fish and shellfish was studied. The isolation protocol included a pre-enrichment, followed by two selective enrichment steps and plating on three selective agars. Listeria monocytogenes could be detected in 17.2% of finfish and 12.1% of shellfish. L. innocua was the most common species encountered. In 6.9% finfish and 5.6% shellfish, both L. monocytogenes and L. innocua were detected. Polymerase chain reaction (PCR)-based amplification of internal fragments of the iap gene was found to be useful in differentiation of L. monocytogenes from L. innocua.