Preliminary study of multidrug-resistant Salmonella Typhimurium and its monophasic variant Salmonella I 4,12: i :- ST 36 isolated from animals in Malaysia

Abstract

Salmonella Typhimurium and its monophasic variant, Salmonella I 4,12:i:- are significant zoonotic pathogens commonly associated with multidrug resistance. While Salmonella Typhimurium has been widely studied, the epidemiology and resistance profiles of the monophasic variant remain underexplored in Malaysia. This study analysed an archived collection of 18 strains, comprising ten Salmonella Typhimurium and eight Salmonella I 4,12:i:- isolates from chickens, pigs, and ducks at the Veterinary Research Institute between 2020 and 2023. Antimicrobial susceptibility testing using disk diffusion method and multi-locus sequence typing were performed to characterize these isolates. A high prevalence of multidrug resistance was observed, with 90% of Salmonella Typhimurium and 87.5% of Salmonella I 4,12:i:- isolates resistant to more than three antimicrobial classes, including 100% resistance to macrolides (erythromycin, tilmicosin). Notably, resistance to third-generation cephalosporins (ceftiofur and cefotaxime) was identified in one Salmonella I 4,12:i:- strain isolated from chickens. MLST analysis revealed that all three selected isolates belonged to sequence type ST36. The findings highlight the zoonotic potential and multidrug resistance challenges posed by Salmonella I 4,12:i:-. The detection of resistance to critical antibiotics, including third-generation cephalosporins raises public health concerns. This study underscores the urgent need for enhanced surveillance, antimicrobial stewardship, and preventive measures to mitigate the public health risks associated with multidrug resistance Salmonella strains, particularly the monophasic variant in Malaysia. Further research into resistance mechanisms and local epidemiology is essential to inform effective control strategies.