ISOLATION AND CHARACTERIZATION OF NISIN-PRODUCING LACTOCOCCUS-LACTIS SUBSP LACTIS FROM BEAN-SPROUTS

Bacterial isolates from bean-sprouts were screened for anti-Listeria m anocytogenes bacteriocins using a well diffusion method. Thirty-four o f 72 isolates inhibited the growth of L. monocytogenes Scott A. One, H PB 1688, which had the biggest inhibition zone against L. monocytogene s Scott A, was selected for subsequent analysis. Both ribotyping and D NA sequencing of 16S ribosomal RNA gene demonstrated that the isolate was Lactococcus lactis subsp. lactis. Polymerase chain reaction and nu cleotide sequencing revealed that the genomic DNA of the bean-sprout i solates 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. W hen co-cultured with L. monocytogenes in MRS broth, the isolate inhibi ted 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. monocy togenes by 1-1.4 logs after storage for 10 d at 7 degrees and 10 degre es C. A bacteriocin-producing Enterococcus faecium was also able to re duce the numbers of L. monocytogenes on Caesar salad, but did not act synergistically when co-inoculated with L. lactis subsp. lactis.