Diversity of Listeria Ribotypes Recovered from Dairy Cattle, Silage, and Dairy Processing Environments

Abstract
Listeria strains isolated over the past 10 years from farms and dairy processing environments were subjected to strain-specific ribotyping using the automated Riboprinter microbial characterization system, alpha version (E. I. du Pont de Nemours & Co., Inc.). A total of 388 Listeria isolates from 20 different dairy processing facilities were examined along with 44 silage, 14 raw milk bulk tank, and 29 dairy cattle (26 udder quarter milk, 1 brain, 1 liver, and 1 aborted fetus) isolates. These 475 isolates included 93 L. monocytogenes, 362 L. innocua, 11 L. welshimeri, 6 L. seeligeri, 2 L. grayi, and 1 L. ivanovii strains. Thirty-seven different Listeria ribotypes (RTs) comprising 16 L. monocytogenes (including five known clinical RTs responsible for foodborne listeriosis), 12 L. innocua, 5 L. welshimeri, 2 L. seeligeri, 1 L. ivanovii, and 1 L. grayi were identified. Greatest diversity was seen among isolates from dairy processing facilities with 14 of 16 (87.5%) of the L. monocytogenes RTs (including five ...

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