The U.S. Department of Agriculture’s Agricultural Research Service (USDA ARS) recently published a study that observed a population of 181 shiga toxin-producing Escherichia coli (STEC) O157:H7 strains over a period of 23 years. The study aims to understand how STEC O157:H7 populations evolve over time and provide context into strain relatedness in foodborne illness outbreak investigations. STEC O157:H7 is of particular concern as it can cause serious, and sometimes fatal, foodborne illness.

STEC O157:H7 is known to reside in cattle feedlots. The retrospective study collected data from a closed-system feedlot at the U.S. Meat Animal Research Center. All 181 strains collected in the study were subjected to short-read sequencing, and a subset of 36 strains were also subjected to long-read sequencing.

The study’s findings suggest that diverse subpopulations of STEC O157:H7 can coexist in the same ecological niche, and that strains may be persistent for a long period of time within the same feedlot. Four distinct clades (groups) of the pathogen were observed, with six strains not classified into one of the four main clades. The existence of the six outlier strains in the study could also reveal what happens when a less competitive strain is introduced from an outside source and is unable to compete with resident strains.

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