The Role of Escherichia coli Porins OmpC and OmpF in Antibiotic Cross Resistance Induced by Sub-Lethal Levels of Kanamycin

Previous studies have shown that pretreatment of E. coli with low doses of kanamycin have generated an increase in the resistance to high doses of kanamycin as well as induced cross resistance to a broad range of unrelated antibiotics, and that multiantibiotic-resistant E. coli had lower levels of OmpF porin. In this study, the role of OmpC and OmpF porins in the development of cross resistance was investigated by comparing the levels of these porins in kanamycin untreated and pretreated E. coli K-12. To demonstrate the difference in protein levels, outer membrane protein fractions from wild type, ΔompC, and ΔompF strains were isolated by French press and analyzed by SDS-PAGE. Minimal Inhibitory Concentration (MIC) assays were used to confirm the development of the cross resistance due to exposure to low doses of kanamycin and related to the levels of porins visualized using SDS-PAGE. Outer membrane protein profile of the wild type showed lower levels of OmpC after pretreatment with kanamycin. Kanamycin pretreatment did not seem to alter the outer membrane protein profiles of both mutant strains. Surprisingly, the ΔompF strain had outer membrane protein profile identical to that of the wild type strain. Resistance to kanamycin of both mutants was 32fold higher than that of the wild type. Upon kanamycin pretreatment, only the wild type showed a slight but reproducible increase in MIC. E. coli K-12 mutant strains ΔompC and ΔompF did not display any reproducible changes in MIC in response to kanamycin pretreatment. Our results indicated that OmpC porin may have a role in the development of resistance to kanamycin in the wild type E. coli K-12, but it is an unlikely factor in development of cross resistance to other tested antibiotics. The role of OmpF in the cross resistance could not be clearly identified.