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Isolation and
characterization of nisin-producing Lactococcus lactis subsp. lactis from
bean-sprouts.
J Appl Microbiol 1997 Oct;83(4):499-507
Cai Y, Ng LK, Farber JM.
Department of Microbiology and Immunology, University of Ottawa, Ontario,
Canada.
Bacterial isolates from bean-sprouts were screened for anti-Listeria
monocytogenes bacteriocins using a well diffusion method. Thirty-four of 72
isolates inhibited the growth of L. monocytogenes Scott A. One, HPB 1688, which
had the biggest inhibition zone against L. monocytogenes Scott A, was selected
for subsequent analysis. Both ribotyping and DNA sequencing of 16S ribosomal RNA
gene demonstrated that the isolate was Lactococcus lactis subsp. lactis.
Polymerase chain reaction and nucleotide sequencing revealed that the genomic
DNA of the bean-sprout isolates contained a nisin Z structural gene. In MRS
broth, bean-sprout isolate HPB 1688 survived at 3-4.5 degrees C for at least 20
d, grew at 4 degrees C and produced anti-listerial compounds at 5 degrees C.
When co-cultured with L. monocytogenes in MRS broth, the isolate inhibited the
growth of L. monocytogenes at 4 degrees C after 14 d and at 10 degrees C after 2
d. When co-inoculated with 10(2) cells g-1 of L. monocytogenes on fresh-cut
ready-to-eat Caesar salad, L. lactis subsp. lactis (10(8) cells g-1) was able to
reduce the number of L. monocytogenes by 1-1.4 logs after storage for 10 d at 7
zero and 10 degrees C. A bacteriocin-producing Enterococcus faecium was also
able to reduce the numbers of L. monocytogenes on Caesar salad, but did not act
synergistically when co-inoculated with L. lactis subsp. lactis.
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