STEC Prevention Insight Through Collaborative Study from MSU Researchers

A collaborative study at Michigan State University could lead to Escherichia coli (E. coli) bacteria prevention practices in the cattle farming industry. Published in Applied and Environmental Microbiology, the study involved the cooperative efforts of the university’s animal scientists, epidemiologists, microbiologists, graduate students, veterinarians, undergraduates, and farmers.

Most forms of E. coli are harmless and even an important part of a healthy human intestinal tract. However, Shiga toxin-producing Escherichia coli (STEC) strains are linked to more serious human infections. It is an important food-borne pathogen that can cause hemorrhagic colitis and hemolytic uremic syndrome.

Most of what we know about STEC comes from studies of E. coli O157 infection, first identified as a pathogen in 1982. According to the Centers for Disease Control and Prevention (CDC), “The most commonly identified STEC in North America is E. coli O157:H7 (often shortened to E. coli O157 or even just “O157”). When you hear news reports about outbreaks of “E. coli” infections, they are usually talking about E. coli O157.” Much less is known about non-O157 STEC, this is because, as a whole, the non-O157 serogroups are less likely to cause severe illness. An estimated 265,000 infections of STEC occur annually in the United States and STEC O157 causes about 36% of these infections.

STEC can be transmitted through contaminated water and food or through contact with contaminated animals or persons. Cattle is the primary reservoir for STEC, and food or water contaminated with cattle feces is the most common source of infections in humans.

The researchers conducted a cross-sectional study of 1096 cattle in six dairy herds and five beef herds in the summers between 2011—2012. Fecal samples were obtained from each animal and cultured for STEC. The goal was to identify epidemiological factors associated with E. coli shedding.

The researchers found, “The prevalence of STEC was higher in beef (21%) versus dairy (13%) cattle (odds ratio (OR):1.76; 95% confidence interval (CI):1.25, 2.47) with considerable variation across herds (range: 6% to 54%). Dairy cattle were significantly more likely to shed STEC when the average temperature was >28.9°C 1-5 days prior to sampling (OR:2.5; 95% CI:1.25, 4.91), during their first lactation (OR:1.8; 95% CI:1.1, 2.8), and when they were <30 days in milk (OR:3.9; 95% CI:2.1, 7.2).”

According to the data, stress or negative energy balance associated with lactation may result in increased STEC shedding frequencies in Michigan during warm summer months. This lead to strategies aimed at reducing stress during lactation or isolating high-risk animals to reduce herd-level shedding and avoid transmission of STEC to susceptible animals and people.

The researchers suggest that future studies focus on, “the isolation of high-risk animals to decrease herd-shedding levels and the potential for contamination of the food supply.” STEC-shedding frequencies varied considerably across cattle herds with shedding of non-O157 serotypes far exceeding the shedding frequencies of O157. This is congruent with human infections in the state of Michigan.

The need to examine different STEC strains that are shed will help determine the rate at which cattle in Michigan acquire new strains over time. This will help researches determine which types of strains are most commonly linked to disease in humans.