Listeria species in seafood: isolation and characterization of Listeria spp. from seafood in San Luis, Argentina

One hundred seafood samples (fish, squid and mussel) were collected from the Argentine Atlantic coast and screened for Listeria spp. The isolates were characterized by biochemical tests, serotyping, phage typing and macrorestriction enzymes analysis of DNA (pulsed-field gel electrophoresis). The overall frecuency (n=100) ofListeria spp. was 12%. Of the 12 isolated strains, three strains isolated from different squid samples were identified as L. monocytogenes and nine strains from fish, mussels and squid as L. innocua. All three L. monocytogenes strains belonged to serovar 4b; eight strains of L. innocua were serovar 6a and one strain of L. innocua was serovar 6b. All three L. monocytogenes strains, but only one of the nine L. innocua strains, were phage-typeable. One restriction profile was detected with Apa I and Asc I for L. monocytogenes strains and three with the same enzymes for L. innocua strains. The combination of these patterns allowed definition of four distinct groups within the 12 strains. The results of this study showed that phenotypic methods remain appropriate but that pulsed-field gel electrophoresis is useful for epidemiological purposes.