Bacteriocin production, plasmid content and plasmid location of enterocin P structural gene in enterococci isolated from food sources

AIMS: To characterize bacteriocin production, antimicrobial spectrum and plasmid content in bacteriocinogenic enterococci from foods. METHODS AND RESULTS: Bacteriocinogenic Enterococcus faecium (14 isolates) and Enterococcus faecalis (three isolates) showed two different patterns of bacteriocin production in liquid broth: exponential-phase and stationary-phase production. Bacteriocin concentrates from all enterococci were inactivated by trypsin, but seldom by heat (100-117 degrees C), extremes of pH (2.0 to 9.0) or reducing agents (such as dithiothreitol). All bacteriocin concentrates were active against Listeria innocua and Listeria monocytogenes, and most were also active against many Ent. faecalis and Ent. faecium isolates. Enterococci clustered in three main groups according to their plasmid content (which included plasmids from 2.0 to 53 kb). Several isolates from different foods showed almost identical plasmid profiles. The enterocin P structural gene (entP) was detected by hybridization on plasmids of c. 19, 26 and/or 35-38 kb. CONCLUSIONS: Enterococci from food show different patterns of bacteriocin production and different plasmid content in spite of carrying similar bacteriocin-encoding genes. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides information on the diversity of bacteriocinogenic enterococci from food sources carrying apparently similar enterocin genes.