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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: Occurrence of generic E. coli, E. coli O157:H7 and Salmonella spp. in water and sediment from leafy green produce farms and streams on the Central California coast

Authors
item Benjamin, Lisa -
item Atwill, Edward -
item Jay-Russell, Michele -
item Cooley, Michael
item Carychao, Diana
item Gorski, Lisa
item Mandrell, Robert

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 2013
Publication Date: April 11, 2013
Citation: Benjamin, L., Atwill, E.R., Jay-Russell, M., Cooley, M.B., Carychao, D.K., Gorski, L.A., Mandrell, R.E. 2013. Occurrence of generic E. coli, E. coli O157:H7 and Salmonella spp. in water and sediment from leafy green produce farms and streams on the Central California coast. International Journal of Food Microbiology. 10.1016/j.ijfoodmicro.2013.04.003 165(1)65-76.

Interpretive Summary: Irrigation with water of poor microbiological quality can elevate levels of bacteria on produce. This study aimed to identify climate and management covariates associated with generic E. coli in irrigation water on leafy green produce farms and to measure the prevalence of E.coli O157:H7 and Salmonella spp.in irrigation and non-irrigation water sources on these farms. Two hundred and fifty-six water and 192 sediment samples were collected from various points along irrigation systems, as well as from streams and ponds on farms on the Central California coast between May 27, 2008 and October 26 , 2010. All samples were cultured for generic E. coli and E. coli O157:H7, and a subset (n=397) was cultured for Salmonella. Mean concentration of E. coli for water and sediment samples, not including those from Moore swabs, was 7.1 x 102 cfu/100 mL and 1.0 x 104 cfu/100 g, respectively. Matched by collection day, E.coli concentration in sediment (cfu/100 g) was typically 10- to 1000-fold higher than the overlying water(cfu/100 mL)for these irrigation systems. Pre-foliar irrigation water samples(wells, reservoirs, irrigation pipe), exceeded the 126, 235, and 576 cfu/100 mL limits by 17%,8% and 3%, respectively. Generic E. coli concentration was positively associated with 24-hour cumulative rainfall and negatively associated with increasing distance between sample location and nearby vegetation or riparian habitat. Moore swabs detected a higher proportion of E. coli O157:H7(13.8%) positive water samples compared to grab samples (1.8%); 1.7% of sediment samples had detectable levels of this pathogen. Interestingly, proximity to livestock and season were not significantly associated with E. coli O157:H7 presence in water or sediments from produce farms or water sources with public access. Salmonella was detected in 6% (6/96)water and 4.3% (3/70) sediment samples. Generic E. coli concentration was not significantly associated with the presence of either E. coli O157:H7 or Salmonella in water or sediment samples, suggesting that, for this 2.5-year period and geographical location, generic E. coli would likely be an unreliable indicator bacteria for predicting the presence of these food-and waterborne pathogens in a key produce production environment.

Technical Abstract: Irrigation with water of poor microbiological quality can elevate levels of bacteria on produce. This study aimed to identify climate and management covariates associated with generic E. coli in irrigation water on leafy green produce farms and to measure the prevalence of E. coli O157:H7 and Salmonella spp.in irrigation and non-irrigation water sources on these farms. Two hundred and fifty-six water and 192 sediment samples were collected from various points along irrigation systems, as well as from streams and ponds on farms on the CentralCalifornia coast between May 27th, 2008 and October 26th , 2010. All samples were cultured for generic E. coli (cfu/100 mL or cfu 100 g) and E. coli O157:H7, and a subset (n=397) was cultured for Salmonella. Covariates were based on grower’s management practices, landscape features in proximity to samples (e.g.,distance to roads and ranches/livestock), and climate data were accessed from an online database. Negative binomial regression models were constructed to test associations between generic E. coli (cfu/100 mL) in water and covariates. Mean concentration of E. coli for water and sediment samples, not including those from Moore swabs, was 7.1 x 102 cfu/100 mL and 1.0 x 104 cfu/100 g, respectively. Matched by collection day, E. coli concentration in sediment (cfu/100 g) was typically 10- to 1000-fold higher than the overlying water(cfu/100 mL) for these irrigation systems. Pre-foliar irrigation water samples(wells, reservoirs, irrigation pipe), exceeded the 126, 235, and 576 cfu/100 mL limits by 17%,8% and 3%, respectively. Generic E. coli concentration was positively associated with 24-hour cumulative rainfall and negatively associated with increasing distance between sample location and nearby vegetation or riparian habitat. Moore swabs detected a higher proportion of E.coli O157:H7 (13.8%) positive water samples compared to grab samples (1.8%); 1.7% of sediment samples had detectable levels of this pathogen. Interestingly, proximity to livestock and season were not significantly associated with E. coli O157:H7 presence in water or sediments from produce farms or water sources with public access. Salmonella was detected in 6% (6/96) water and 4.3% (3/70) sediment samples. Generic E. coli concentration was not significantly associated with the presence of either E. coli O157:H7 or Salmonella in water or sediment samples, suggesting that, for this 2.5-year period and geographical location, generic E. coli would likely be an unreliable indicator bacteria for predicting the presence of these food- and waterborne pathogens in a key produce production environment.

Last Modified: 10/21/2014
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