Detection and antimicrobial susceptibility of E. coli O157:H7 in the milk supply chain, milking environments and humans in Woliata Sodo, Ethiopia.

Background: Escherichia coli O157:H7 is a strain that produces Shiga toxin, which can cause infections ranging from mild to severe in humans. Cattle are a primary reservoir for the bacteria, and the contaminated milk and milk products can transmit these bacteria to humans, posing a risk of infection. The present study aimed to evaluate the occurrence of E. coli O157:H7 and determine its antimicrobial susceptibility profile across the milk supply chain, milking environments, and humans in Woliata Sodo, Southern Ethiopia.

Methodology: A total of 644 samples, including raw milk, hand swabs, teat swabs, equipment swabs, floor swabs, and human stool, were collected through a cross sectional study. Bacterial detection was performed according to the ISO 16,654 standard method, and the antimicrobial susceptibility of the isolates was evaluated using the Kirby-Bauer disk diffusion method against 14 antimicrobials representing ten different classes.

Results: The overall detection rate of E. coli O157:H7 was 3.1% (20/644). The highest detection rate was observed in milk samples collected at milk collecting centers, at 10% (5/50). In comparison, detection rates were 6.8% (4/59) in samples from milkers' hands, 5.4% (2/37) in farm floor swabs, and 2.9% among outpatients presenting with diarrhea. All the isolates showed resistance to doxycycline, erythromycin, tetracycline, clindamycin, and vancomycin. Additionally, 95%, 90%, and 90% of isolates were resistant to amoxicillin, ampicillin, and streptomycin, respectively. Resistance was lower for ceftriaxone (20%) and chloramphenicol (15%). A significant proportion (100%) of the isolates exhibited multidrug resistance.

Conclusion: This study confirmed the presence of multidrug resistant E. coli O157:H7 in the tested sample. Notably, the highest prevalence was detected in milk samples from collection centers, underscoring post harvest contamination as a critical point of intervention. Identification of the pathogen on milkers' hands, farm floors, and human stool samples highlights potential transmission pathways and suggests a tangible risk of foodborne infections. These findings emphasize the critical need for targeted public health strategies, including comprehensive education on hygienic practices and the implementation of effective contamination control measures, to reduce the risk of infection and protect consumer health.