Phenotypic and molecular characterization of Listeria monocytogenes strains isolated from a marine environment in Morocco

Microbiological analysis of 1025 marine samples, including 345 from seawater, 337 from shellfish, and 343 from sediments collected between January 2000 and December 2002 from 18 shellfish sites on the Atlantic coast of mid-west of Morocco (Agadir region), yielded 143 strains of Listeria (Listeria monocytogenes: 38; L. innocua: 109; L. ivanovii: 1). The overall incidence of Listeria sp. in the coastal environment was 5.3%. Thirteen L. monocytogenes strains were isolated from seawater, 7 from sediment, and 12 from shellfish. The 38 strains of L. monocytogenes were phenotypically characterized. All belonged to two chemotypes according to appareillage et procede d'identification (API) Listeria classification: 8 strains were type 2510, alpha-mannosidase-negative and hemolytic; and 30 strains were type 6510, alpha-mannosidase-positive, of which 8 strains were nonhemolytic. All the L. monocytogenes strains belonged to the 1/2 serogroup, with serovar 1/2b clearly prevalent (78.9%), although some nonhemolytic strains were serovar 1/2a. This collection of L. monocytogenes strains included 6 different pulsotypes as assessed by DNA macrorestriction with the restriction enzymes AscI and ApaI.