Prevalence and Antimicrobial Susceptibility of Salmonella enterica in Milk supply chain, Humans, and milking environment in Woliata Sodo, Ethiopia

Background : Foodborne disease caused by Salmonella enterica is among the leading causes of death worldwide. Few studies have been conducted on the prevalence of Salmonella enterica contamination along milk supply chain, which is important for reducing public health risks. The objectives of this study were to estimate the prevalence of Salmonella enterica in milk along supply chain; milking environment (floor, teat surface, and storage containers); milkers’ hands, diarrheic patients and to assess the antimicrobial susceptibility profile of the isolates in Wolaita Sodo, Ethiopia. Methodology : A cross-sectional study design was used to collect a total of 644 samples from 106 dairy farms, comprising tank bulk milk (n=106), cow’s milk (n=133), milkers’ hand swabs (n=59), teat surfaces (n= 51), floors (n= 37), milk storage containers (n=55), collectors’ bulk milk (n= 50), retailers’ bulk milk (n= 50), and stool from diarrheic patients (n= 103). The isolation and identification of Salmonella enterica were performed following standard bacteriological methods, and antimicrobial susceptibility was tested using the Kirby–Bauer disk diffusion method against 14antimicrobials. Results : The overall prevalence of Salmonella enterica was 19.6% (126/644; 95% CI: 16.6 –226–22.8). The highest prevalence (28.8%; 95% CI: 17.7 – 42.1) was observed in hand swab samples, while the lowest was observed in bulk milk samples (14.2%; 95% CI: 8.1 – 22.3). The prevalence was 24.3% (49/202; 95% CI: 18.52 – 30.77) in the milking environment, 18% (61/339; 95% % CI: 14.1 - 22.5) in the milk supply chain samples and 15.5% (16/103; 95% CI: 9.2- 23.9) in the diarrheic patient samples. However, the difference in the prevalence of Salmonella among the different sample types was not statistically significant (Chi-squared = 8.12; p = 0.422). Among the Salmonella isolates tested, 89.7%, 88.5%, 77.8%, 77.8%, 66.7% and 63.3% were resistant to amoxicillin, ceftazidime, ampicillin, streptomycin, doxycycline, and tetracycline, respectively. All the isolates were susceptible to norfloxacin, and 81% of them were susceptible to ciprofloxacin. Multidrug resistance (MDR) was detected in 88% (44/50) of the isolates. The MDR was higher at the farm than milk collectors and retailers. Conclusion and Recommendation : Our study revealed a high prevalence of Salmonella enterica along the milk supply chain, in milking environment, and in humans, suggesting the need for intervention. The isolates were phenotypically resistant to most antimicrobials used in the medical and veterinary practices. Moreover, the antimicrobial resistance profile and MDR indicates the emergence of innovation of drug of choice for the treatment of disease of human and animals. Further studies on the genetic relatedness of the isolates from different sources, quantifying the risk of consumption of milk contaminated with Salmonella enterica and identifying the determining factors are required to design tailored and effective measures to ensure milk safety.