Occurrence and characterization of multidrug resistant Shigella spp. in a dairy farm environment: a one health...

This study investigated the occurrence of antibiotic-resistant Shigella spp. within a dairy farm environment by examining 200 samples collected from cattle (milk, faeces), environmental sources (drinking water, dairy wastewater, milking machine swabs), and human handlers. Shigella spp. was detected in 8.5% of samples, with the highest occurrence in dairy wastewater (52.94%) and feces (35.29%). S. flexneri was the predominant species identified, while S. dysenteriae and S. sonnei were less frequent. Notably, no Shigella spp. were found in milk or handler swabs. High antibiotic resistance was observed, with complete resistance to ampicillin (100%), followed by tetracycline (82.4%) and cefoxitin (58.8%). Conversely, isolates were largely susceptible to meropenem (94.1%), ampicillin-sulbactam (94.1%), and cefepime (88.2%). Multidrug resistance (MDR) was common, affecting 70.6% of isolates. Phenotypic tests confirmed extended-spectrum β-lactamase (ESBL) production in ten isolates and AmpC production in eight cefoxitin-resistant isolates. The multiple antibiotic resistance (MAR) index was ≥ 0.2 in 94.1% of isolates. Genotypic analysis revealed a high prevalence of tetracycline resistance genes (tetA, tetB; 70.5%), plasmid-mediated quinolone resistance genes (qnrS, qnrB; 58.8%), and bla_AmpC gene (52.9%). ESBL genes (bla_TEM-1, bla_SHV-1, bla_CTX-M-9) were present in 17.6% of isolates, while the trimethoprim resistance gene (dfrA17) was detected in 5.8%. Chi-square analysis confirmed significant differences in prevalence, resistance profiles, and gene distribution (p < 0.05). These findings highlight the occurrence of multidrug-resistant Shigella spp. within the dairy farm ecosystem, underscoring their potential role in the dissemination of antibiotic resistance and posing an emerging public-health concern.