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United States Department of Agriculture

Agricultural Research Service

Research Project: Biology and Control of Human Pathogens on Fresh Produce

Location: Produce Safety and Microbiology Research

Title: Prevalence of Shiga toxin producing Escherichia coli, Salmonella enterica and Listeria monocytogenes at public access watershed sites in a California central coast agricultural region

Authors
item Cooley, Michael
item Quiñones, Beatriz
item Oryang, David -
item Mandrell, Robert -
item Gorski, Lisa

Submitted to: Frontiers in Cellular and Infection Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 16, 2014
Publication Date: March 4, 2014
Citation: Cooley, M.B., Quinones, B., Oryang, D., Mandrell, R.E., Gorski, L.A. 2014. Prevalence of Shiga toxin producing Escherichia coli, Salmonella enterica and Listeria monocytogenes at public access watershed sites in a California central coast agricultural region. Frontiers in Cellular and Infection Microbiology. 4:30.

Interpretive Summary: Produce contaminated with enteric pathogens is a major source of foodborne illness in the United States. Surface water regions serves as both a source and a vehicle for transport of pathogens to produce in the field. Lakes, streams, rivers, and ponds at 30 locations in the vicinity of a leafy green growing region on the Central California Coast were sampled bi-monthly for over two years to determine the prevalence of Shiga toxin producing Escherichia coli (STEC), Salmonella enterica, and Listeria monocytogenes. The prevalence of STEC from 1,386 samples was 11%; 110 samples (8%) contained E. coli O157:H7 with the highest prevalence occurring close to cattle operations. Salmonella prevalence in 1,405 samples was 65% resulting in 996 isolates. There was a lower prevalence of Salmonella in late autumn, before the start of the traditional rainy season. Analysis by Pulsed Field Gel Electrophoresis indicated certain pulsotypes were persistent and transported in the region over several years. L. monocytogenes prevalence was 43% of 1,405 samples resulting in 635 individual isolates. Over 85% of the isolates belonged to serotype 4b with serotypes 1/2a, 1/2b, 3a, 4d and 4e representing the rest. Although the watershed sites tested are not used for irrigation directly, they can flood the edges of fields during heavy rains, and are accessible by wildlife.

Technical Abstract: Produce contaminated with enteric pathogens is a major source of foodborne illness in the United States. Surface water regions serves as both a source and a vehicle for transport of pathogens to produce in the field. Lakes, streams, rivers, and ponds at 30 locations in the vicinity of a leafy green growing region on the Central California Coast were sampled with Moore swabs bi-monthly for over two years to determine the prevalence of Shiga toxin producing Escherichia coli (STEC), Salmonella enterica, and Listeria monocytogenes. The prevalence of STEC from 1,386 samples was 11%; 110 samples (8%) contained E. coli O157:H7 with the highest prevalence occurring close to cattle operations. Of 152 samples positive for STEC, 578 isolates representing major clinical O-types were characterized, and 330 (57%) contained both shiga toxin types 1 and 2 and intimin. Multiple Locus Variable Number Tandem Repeat Analysis of STEC isolates indicated prevalent strains during the period of study. Salmonella prevalence in 1,405 samples was 65% resulting in 996 isolates. There was a lower prevalence of Salmonella in late autumn, before the start of the traditional rainy season. There were 2, 8 and 14 sites that were Salmonella-positive over 90%, 80% and 70% of the time, respectively. All Salmonella isolates contained invA. The serotypes identified most often were 6,8:d:-, Typhimurium, and Give. Analysis by Pulsed Field Gel Electrophoresis indicated certain pulsotypes were persistent and transported in the region over several years. L. monocytogenes prevalence was 43% of 1,405 samples resulting in 635 individual isolates. Over 85% of the isolates belonged to serotype 4b with serotypes 1/2a, 1/2b, 3a, 4d and 4e representing the rest, and there were 12 and 2 sites that were positive over 50% and 80% of the time, respectively. Although the watershed sites tested are not used for irrigation directly, they can flood the edges of fields during heavy rains, and are accessible by wildlife.

Last Modified: 10/20/2014
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