An adult chicken mortality case investigation: coinfection by Salmonella Indiana and Kentucky

Abstract Coinfection, the simultaneous invasion of multiple pathogens into a single host, is a critical but understudied area, especially in the farm animal sector. We report a unique and unusual fatal case of coinfection with S . Indiana and S . Kentucky, which has rarely been studied in the literature and could hold potential importance for veterinary clinics. In silico analysis revealed that all the isolates exhibited extensive multidrug resistance. By analyzing the plasmids, two replicons, IncHI2 and IncHI2A, were detected in S . Indiana, whereas no plasmids were detected in S . Kentucky. Chicken embryo lethality assays demonstrated that both S . Indiana and S . Kentucky caused 100% mortality by the third day post infection, significantly exceeding the lethality of the control strains. These findings emphasize the high pathogenic potential of these serovars, especially S . Indiana, which carries the cdtB gene encoding typhoid toxin, further confirming its increased pathogenicity. Overall, our results underscore the urgent need to improve biosecurity measures to mitigate the risk of coinfections involving multidrug-resistant Salmonella strains in poultry production environments.