Antimicrobials Produced by Wild Lactococcal Strains Isolated from Homemade Cheeses

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Abstract
Wild lactococcal strains isolated from different homemade cheeses were tested for antimicrobial activities. Fifty percent of them were inhibitory to at least one lactococcal indicator. Twenty-three of the producer strains were selected on the basis of their technological properties and their inhibitory products characterized with respect to their chemical nature, heat sensitivity and spectrum of inhibition. Plasmid profiles were used to differentiate the producer strains. As determined by polymerase chain reaction, 21 out of the 23 strains harbored a nisin-related encoding gene. Furthermore, sequencing of the amplicons obtained from 7 isolates representing each of the plasmid profiles found revealed the presence of the nisin Z gene in all of them. Amplification was negative for the strains IPLA 525 and IPLA 972. The product synthesized by this last strain showed no sensitivity to treatment with proteases; it was heat inactivated and showed a narrow inhibitory spectrum restricted to other lactococci.

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