The two component system PHOP/PHOQ is required for full chloramphenicol resistance in the multiresistant Salmonella typhimurium DT104

Salmonella enterica serovar typhimurium phage type DT104 with multiple antibiotic resistance to streptomycin, chloramphenicol, tetracycline, ampicillin and sutfonamides is becoming an increasing cause of disease in humans, cattle and pigs. The floR (cmlA) gene, conferring chloramphenicol and florfenicoL resistance shows structural similarity to multidrug efflux transporters driven by the proton motive force. We show now that the resistance to chloramphenicol mediated by the floR (cmlA) gene needs a functional PhoP-PhoQ regulatory system. We hypothesise that PhoP-PhoQ induced changes in the bacterial membrane are required for an effective antiport of this multidrug efflux systems and to establish a sufficient proton motive force of the transmembrane electrochemical proton gradient.