Colistin Resistance-Mediated Bacterial Surface Modification Sensitizes Phage Infection

Abstract

Colistin is a drug of last resort for the treatment of many multidrug-resistant Gram-negative bacteria, including carbapenem-resistant Klebsiella pneumoniae (CRKP). However, bacteria readily acquire resistance to this antibiotic via lipopolysaccharide modifications caused by spontaneous mutations or from enzymes acquired by lateral gene transfer. The fitness cost associated with these modifications remains poorly understood. In this report, we show that colistin-resistant CRKP is more susceptible to killing by a newly isolated lytic phage than the colistin-sensitive parent strain. We observed this behavior for colistin resistance conferred by a horizontally transferred mcr-1-containing plasmid and also from the inactivation of the chromosomal gene mgrB. By measuring zeta potentials, we found that the phage particles were negatively charged at neutral pH and that colistin-resistant bacteria had less negative zeta potentials than did the wild type. These results suggest that the decreased negative surface charge of colistin-resistant cells lowers the level of electrostatic repulsion between the phage and bacteria, thereby promoting phage adherence and subsequent infection. To further explore this, we tested the effect of phage treatment on CRKP growing in several different environments. We found that colistin-resistant cells were more susceptible to phage than were the wild-type cells when growing in biofilms or infected moth larvae and when colonizing the mammalian gut. A better understanding of these fitness costs may lead to new treatment approaches that minimize the emergence and spread of colistin-resistant pathogens in human and environmental reservoirs.

Pleiotropy complicates a trade-off between phage resistance and antibiotic resistance

“…It is possible that phage-selected mutations in rfa genes change the LPS structure in such a way that makes it more susceptible to colistin disruption, resulting in the evolutionary trade-off between phage resistance and colistin resistance. Consistent with this result, Hao et al (26) recently found a similar trade-off in the complementary direction, observing that selection for colistin resistance resulted in reduced phage resistance, indicating that this trade-off may evolve in either direction. Although LPS-related mutations were generally less abundant than tolC mutations after experimental evolution with phage U136B, we found that the LPS mutants did not necessarily go extinct (SI Appendix, Supplementary Results and SI Appendix, Table S5), indicating their potential importance in phage treatments of infections.…”

Identification of Novel phoP-phoQ Regulated Genes that Contribute to Polymyxin B Tolerance in Pseudomonas aeruginosa

“…In addition, formation of biofilm drastically enhances the bacterial resistance to antibiotics [ 7 ]. Polymyxin B and colistin (polymyxin E) are cyclic polypeptide antibiotics that are used as the last-resort treatment option against serious infections caused by Gram-negative bacteria, including P. aeruginosa , Klebsiella pneumoniae , and Acinetobacter baumannii [ 7 , 8 , 9 , 10 ]. Polymyxin B and colistin are very similar in their structures, both consisting of a cyclic heptapeptide, a linear tripeptide, and a fatty acid chain [ 11 ].…”

Phage–antibiotic combinations: a promising approach to constrain resistance evolution in bacteria

“…In some cases, phage resistance is linked with an evolutionary trade-off of increased or regained antibiotic susceptibility (an example of collateral sensitivity); 33,34 and vice versa, antibiotic resistance is sometimes associated with higher phage susceptibility. 35 These genetic trade-offs are one of the ways to impose a direct cost on resistance and to select against antibioticand/or phage-resistant strains. Collateral sensitivity has been extensively studied in antibiotic and cancer combination therapies as a strategy to reduce the emergence of drug resistance.…”

“…Systematic studies evaluating phage collateral sensitivity profiles of antibiotic-resistant bacteria are lacking. However, a recent study by Hao et al 35 indicated that evolved collateral sensitivity to phages and antibiotics in a combination can be reciprocal. The authors observed that a lytic phage was more effective at killing a colistin-resistant K. pneumoniae strain than its colistin-sensitive parent.…”

“…Phages, like antibiotics, impose a selection pressure on bacteria promoting resistance. In some cases, phage resistance is linked with an evolutionary trade‐off of increased or regained antibiotic susceptibility (an example of collateral sensitivity); 33,34 and vice versa, antibiotic resistance is sometimes associated with higher phage susceptibility 35 . These genetic trade‐offs are one of the ways to impose a direct cost on resistance and to select against antibiotic‐ and/or phage‐resistant strains.…”