Prevalence of Escherichia coli O157:H7

Linda F. Benedict, Gutierrez, Myriam, Janes, Marlene E.

Evelyn Gutierrez and Marlene Janes

According to the U.S. Centers for Disease Control (CDC) and Prevention, Escherichia coli (E. coli) are a large and diverse group of bacteria. Most of them are harmless and naturally found in the human intestinal tract, but others can be deadly. Escherichia coli O157:H7 has become an important problem in human health in the United States since it was first reported in 1982. In the past five years, CDC has reported several multistate E. coli O157:H7 outbreaks related to beef, dairy products, fruits and vegetables. People who become infected with E. coli O157:H7 will experience severe stomach cramps and diarrhea with or without blood and vomiting within three to four days after eating contaminated food.

Scientific studies have indicated that cattle herds worldwide are the primary reservoirs of E. coli O157:H7. Cattle carrying E. coli O157:H7 have no symptoms and shed it intermittently and seasonally in their feces. Several outbreaks of E. coli O157:H7 associated with fruits and vegetables in the U.S. between 1986 and 2014 were due to contamination with animal manure during production and at harvest, contamination of water used for washing, or cross-contamination of the raw produce with raw meat products during food preparation. The ability of E. coli O157:H7 to survive in soil and manure for extended periods of time could explain its spread into the water supply and onto crops.

In Louisiana, calves are raised with cows mainly on grass forage until shipped to finishing sites in other states. Knowledge of the prevalence of E. coli O157:H7 associated with small-scale cow-calf farms can help with assessing risks and developing risk management strategies needed to control the colonization of this pathogen within the farm environment.

Large cattle ranches have more resources to purchase specialized equipment that can help prevent cross infection of cattle. Conversely, smaller-scale cattle farms mainly use existing equipment with less sanitary designs that can promote cross infection of cattle. There is a lack of knowledge on the optimal conditions required for the control, reduction and removal of foodborne pathogens from the surfaces of water troughs, feed bins and equipment.

LSU AgCenter scientists have conducted research that could provide additional information to better understand how cattle at the cow-calf stage of production become infected by E. coli O157:H7. From June to December 2011, samples were collected from 27 small-scale cow-calf farms across Louisiana for detection of E. coli O157:H7. Environmental samples collected and tested included fresh fecal pats on the ground, water from troughs and ponds, and swabs from troughs, salt and hay bunks.

From all the samples tested on the 27 farms, E. coli O157:H7 tested positive in 9 percent of the fecal pats, 7 percent of the water samples and 2 percent of the swabbed surfaces, for a total of 51 (8 percent) positive samples. From the 51 E. coli O157:H7-positive samples, 74 percent were fecal pats, 24 percent were water and 2 percent were from swabbed surfaces (Figure 1). Farms from the central region of the state had a higher number of positive samples, compared with the northwest and southwest regions. These results include fecal pats, water and swabs (Table 1).

The results in this study show that although fecal pats had a higher prevalence, water troughs are a source of E. coli O157:H7 as well. On the other hand, the low percentage of positives for the swabs indicated that surfaces in the farm environment have a minor role in the prevalence of this pathogen in cattle operations. The overall prevalence of E. coli O157:H7 in the environment of small-scale cow-calf operations in Louisiana was 8 percent. Additionally, it is important to mention that a proportional relationship between E. coli O157:H7 in fecal pats and in water indicates water could be the principal carrier for the spread of E. coli O157:H7 on farms.

These AgCenter findings can be used to help establish good animal husbandry practices and preharvest food safety conditions for small-scale cowcalf operations to reduce E. coli O157:H7 in cattle.

Evelyn Gutierrez is an instructor, and Marlene Janes is a professor in the School of Nutrition and Food Sciences.

This article was published in the fall 2014 issue of Louisiana Agriculture.

11/13/2014 8:50:43 PM
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