Animal Age is a Factor to Target Developing Pre-harvest Intervention to Reduce Shiga Toxin-producing Escherichia coli

Introduction: Controlling the prevalence of Shiga toxin-producing Escherichia coli (STEC) in cattle at the pre-harvest level is critical to reducing outbreaks of this pathogen in humans. A multilayer of factors, including environmental and bacterial factors, modulates the colonization and persistence of E. coli O157 in cattle, which serve as a reservoir of this pathogen. However, understanding the animal factors, which affect the prevalence of this pathogen remains unknown. 

Purpose: The purpose of this study was to identify animal factors that affect the prevalence of STEC in cattle to provide insights for the development of mitigation strategies at the pre-harvest level.

Methods: Cattle fecal swab samples were collected at the rectal anal junction (RAJ) from 90 animals, which were used twice in this project over the course of two years. Swab samples were plated on MacConkey agar, and incubated at 37°C for 24 hours to isolate lactose fermenting colonies. Twenty pink colonies per plate were analyzed for STEC using multiplex PCR amplifying stx1 and stx2 genes. Pearson’s Chi-squared test was used to compare the prevalence of stx1, stx2, or stx1/2 positive microorganisms in cows and heifers. 

Results: The total number of STEC from the RAJ varied between animals, ranging from 0 to more than 10⁶. The prevalence of STEC (positive with either stx1 or stx2) was 47% and 50% in the 1^st and 2^nd year, respectively, and the majority of positive samples contained this pathogen at 10²-10⁵CFU/swab. The prevalence of STEC was significantly lower (P < 0.01) in heifers compared to cows, indicating animal age plays a key role in the prevalence of STEC. 

Significance: Our data reveal that animal age affects the prevalence of STEC in cattle, providing a potential mitigation strategy to reduce STEC at the pre-harvest level.