Molecular detection and antibiogram of Shiga toxin-producing Escherichia coli (STEC) from raw milk in and around Bahir Dar town dairy farms, Ethiopia

Illnesses associated with consuming infected milk and milk products are a widespread problem in low and middle-income countries. Shiga toxin-producing Escherichia coli (STEC) is a bacterium commonly found in raw milk and causes foodborne diseases ranging from mild diarrhea to severe hemorrhagic colitis and hemolytic uremic syndrome. This study aimed to investigate the virulence gene and antimicrobial resistance profiles of Shiga toxin-producing E. coli strains isolated from raw milk in dairy farms in and around Bahir Dar town. Raw milk samples (n = 128) collected from December 2021 to July 2022 were cultured, and E. coli strains were isolated using standard methods. Shiga toxin-producing E. coli strains were identified genotypically by the presence of the virulence markers using a single-plex polymerase chain reaction. The antibiotic susceptibility testing of Shiga toxin-producing E. coli isolates was done by the agar disk diffusion method. In total, 32 E. coli isolates were recovered from milk samples from lactating animals. PCR screening of these isolates resulted in 19 (59.3%) positives for Shiga toxin-producing E. coli. The stx2 gene was detected in 53% of cases, followed by stx1 (31%) and eae (16%. The STEC isolates were highly sensitive to ciprofloxacin (94.7%) and kanamycin (89.5%), while exhibiting significant resistance to amoxicillin (89.5%) and streptomycin (73.7%). The present study points out the occurrence of virulent and antibiotic-resistant Shiga toxin-producing E. coli strains in raw milk that could pose a potential risk to public health. Further analysis by whole genome sequencing is necessary for an in-depth assessment and understanding of their virulence and resistance factors. Moreover, large-scale studies are needed to identify the prevalence and potential risk factors and to prevent the spread of antibiotic-resistant STEC strains in the milk production chain.