DEVELOPMENT OF NEW ENRICHMENT BROTHS AND PLATING AGARS FOR ISOLATION OF HEMOLYTIC SPECIES OF LISTERIA

Abstract

ABSTRACT A new basal broth medium was formulated for optimal growth of Listeria monocytogenes, which occurred at 37°C when the initial pH was 6.8. This formulation was used as the basal medium for development of a highly selective plating agar which proved suitable for direct culture of vaginal and rectal swabs for L. monocytogenes. A modification with slightly lower selectivity was necessary for recovery of hemolytic strains of Listeria ivanovii and Listeria seeligeri. The same basal medium was used as a pre‐enrichment broth and for the development of a selective enrichment broth which were incorporated into a two‐step enrichment procedure for the isolation of L. monocytogenes from foods. These new media were compared with several others that have been proposed by comparing recoveries of Listeria from laboratory seeded foods (100% positive), raw milk (50 samples, all negative) and comminuted meat products (75% positive).