Prevalence, multidrug resistance patterns, virulence and antimicrobial resistance genes of emerging MDR Aeromonas hydrophila strains retrieved from subclinical bovine mastitis

A study of dairy farms in Cairo, Egypt investigated Aeromonas hydrophila in cases of bovine subclinical mastitis. Among 800 milk samples, subclinical mastitis was detected in 42.5%, and A. hydrophila was identified in 20.8% of these cases. Genetic analysis showed that all isolates carried the aerA virulence gene, with several other virulence genes also frequently present. The bacteria exhibited high resistance to many commonly used antibiotics, including amoxicillin, tetracycline, and ceftriaxone, while remaining largely susceptible to norfloxacin. Notably, a substantial proportion of strains were multidrug-resistant (MDR) or extensively drug-resistant (XDR) and carried multiple resistance genes such as blaTEM, blaCTX-M-1, blaOXA-1, tetA, aadA1, and sul1. The findings provide the first evidence of MDR and XDR A. hydrophila associated with bovine mastitis in Egypt, highlighting a potential One Health public health risk linked to the dairy sector.