Antibiotic resistance in Salmonella enterica serovar typhimurium exposed to microcin-producing Escherichia coli

Microcin 24 is an antimicrobial peptide secreted by uropathogenic Escherich ia coli. Secretion of microcin 24 provides an antibacterial defense mechani sm for E. coh. In a plasmid-based system using transformed Salmonella enter ica, we found that resistance to microcin 24 could be seen in concert with a multiple-antibiotic resistance phenotype. This multidrug-resistant phenot ype appeared when Salmonella was exposed to an E. coli strain expressing mi crocin 24. Therefore, it appears that multidrug-resistant Salmonella can ar ise as a result of an insult from other pathogenic bacteria.