Study: Antibiotic resistance is increasing in Shiga toxin-producing E. coli

Resistance to antimicrobial agents is rising among human infections with Escherichia coli bacteria that produce the Shiga toxin, according to a study analyzing data from nearly 2,000 infections in the United States between 2010 and 2021.

The increase in resistance points to a need for antibiotic stewardship in the food production chain as well as in human health, says study leader Csaba Varga, a professor of epidemiology at the University of Illinois Urbana-Champaign.

Shiga toxin–producing E. coli is a type of foodborne bacteria that can cause anything from mild diarrhea to very serious illness. About 100,000 people in the U.S. get sick from this strain each year, and some end up in the hospital. The biggest concern is for children under five years of age, who are more likely to develop serious complications, such as kidney failure."

Csaba Varga, professor of epidemiology, University of Illinois Urbana-Champaign

Varga and graduate student Tarjani Bhatt used data reported by the U.S. Centers for Disease Control and Prevention, which collects the information through a national surveillance system. They focused on the E. coli strain O157, which produces the Shiga toxin responsible for the majority of severe illnesses. They looked at 1,995 samples collected between 2010 and 2021 to see whether there was any change in antimicrobial resistance rates over time, and whether there were any patterns in age or geography.

"Most of the previous studies have looked at snapshots in time, not how resistance changes year by year. We didn't have a clear picture of long-term trends, whether resistance was increasing, decreasing or staying the same," Varga said. "Resistance doesn't stay in one place; it moves through people, animals and the environment. Our study helps fill those gaps by looking at when, where and in whom resistance is emerging over time."

The group found that, while overall resistance remains low, it has steadily increased over time - especially for the common antibiotics tetracycline and sulfisoxazole. They also found that resistance varied by geographical region and by age group, with younger adults in their 20s and 30s most likely to have infections resistant to some antibiotics. The results are reported in the journal Future Microbiology.

The most mystifying aspect of the findings is that antibiotics are not typically recommended for Shiga-producing E. coli infections, Varga said. Though the treatment kills the bacteria, that action triggers the release of more Shiga toxin, making the illness more dangerous and increasing the risk for serious complications. Antibiotics are avoided unless the patient has another severe infection at the same time.

"Even though we don't usually treat this infection with antibiotics, we're still seeing resistance emerging and spreading, which tells us these bacteria are being exposed to antibiotics somewhere along the way," Varga said.

The researchers propose a "One Health" approach to the issue, taking into account not only human health and antibiotic use, but animals and environment as well, particularly because the illness is foodborne.

"Better antibiotic stewardship in agriculture, along with food safety and environmental controls, will be key to slowing this trend. What happens on farms, in food production and in the environment can directly impact human health. Prevention has to happen from farm to fork," Varga said.