Two resistance nodulation division-family efflux pumps in Chromobacterium species and their role in antibiotic resistance and tolerance
Very little is known of the antibiotic resistance mechanisms of members of the Chromobacterium genus. In previous studies of Chromobacterium subtsugae (formerly C. violaceum) strain CV017, we identified a resistance nodulation division (RND)-family efflux pump (CdeAB-OprM). Here, we show the cdeAB-oprM genes are widely distributed in members of the Chromobacterium genus. We use antimicrobial susceptibility testing with a CV017 cdeAB-oprM mutant to show the products of these genes confers resistance to a variety of antibiotics including ciprofloxacin, a clinically important antibiotic. We also identified a related RND-family pump, cseAB-oprN, in the genome of CV017 and other C. subtsugae species, that is not present in other members of the Chromobacterium genus. We demonstrate that CdeAB-OprM and CseAB-OprN are both transcriptionally induced in CV017 cells treated with sub-lethal antibiotic concentrations and they are important for induction of tolerance to different antibiotics. While CdeAB-OprM has a broad antibiotic specificity, the CseAB-OprN system is highly specific for a ribosome-targeting antibiotic produced by the saprophytic bacterium Burkholderia thailandensis, bactobolin. Finally, we use a previously developed B. thailandensis-C. subtsugae CV017 co-culture model to demonstrate that adding sub-lethal bactobolin at the beginning of co-culture growth increases the ability of CV017 to compete with B. thailandensis in a manner that is dependent on the CseAB-OprN system. Our results provide new information on the antibiotic resistance mechanisms of Chromobacterium species and highlight the importance of efflux pumps during competition with other bacterial species. IMPORTANCEThis study describes two closely related efflux pumps in members of the Chromobacterium genus, which includes opportunistic but often-fatal pathogens and species with highly versatile metabolic capabilities. Efflux pumps remove antibiotics from the cell and are important for antibiotic resistance. One of these pumps is broadly distributed in the Chromobacterium genus and increases resistance to clinically relevant antibiotics. The other efflux pump is present only in Chromobacterium subtsugae and is highly specific for bactobolin, an antibiotic produced by the soil saprophyte Burkholderia thailandensis. We demonstrate these pumps can be activated to increase resistance by their antibiotic substrates, and that this activation is important for C. subtsugae to survive in a laboratory competition experiment with B. thailandensis. These results have implications for managing antibiotic-resistant Chromobacterium infections, bioengineering of Chromobacterium species, and for understanding the evolution of efflux pumps.