ANTIMICROBIALS PRODUCED BY WILD LACTOCOCCAL STRAINS ISOLATED FROM HOMEMADE CHEESES

Wild lactococcal strains isolated from different homemade cheeses were tested for antimicrobial activities. Fifty percent of them were inhib itory to at least one lactococcal indicator. Twenty-three of the produ cer strains were selected on the basis of their technological properti es and their inhibitory products characterized with respect to their c hemical nature, heat sensitivity and spectrum of inhibition. Plasmid p rofiles were used to differentiate the producer strains. As determined by polymerase chain reaction, 21 out of the 23 strains harbored a nis in-related encoding gene. Furthermore, sequencing of the amplicons obt ained from 7 isolates representing each of the plasmid profiles found revealed the presence of the nisin Z gene in all of them. Amplificatio n was negative for the strains IPLA 525 and IPLA 972. The product synt hesized by this last strain showed no sensitivity to treatment with pr oteases; it was heat inactivated and showed a narrow inhibitory spectr um restricted to other lactococci.