Deletion of ompF and ompC in Escherichia coli K12 does not affect kanamycin resistance

OmpC and OmpF are major Escherichia coli outer membrane general diffusion porins that are involved in the influx of small cationic hydrophilic molecules. It has been suggested that these two porins are involved in resistance to antibiotics such as kanamycin. OmpC and OmpF are reciprocally regulated by growth medium osmolarity. At low osmolarity, OmpF is preferentially expressed and at high osmolarity, OmpC is preferentially expressed. Previously reported results for kanamycin susceptibility of ΔompC and ΔompF E. coli K12 mutants are inconsistent. Furthermore, these previous studies were all done under low salt conditions which does not account for the differential expression of OmpC and OmpF under different osmolarities. This study aims to address the discrepancy between previously reported kanamycin resistance of ΔompC and ΔompF mutants by repeating the experiments. The differential expression of the two porins will also be addressed by determining resistance of ΔompC and ΔompF mutants cultured under different medium osmolarities. Minimum inhibitory concentration assays were conducted on E. coli K12 wild type, ΔompC and ΔompF mutants grown under three different salt condition (0.5, 1.0 and 1.5% NaCl) LB media. Results show that deletion of ompC and ompF does not affect kanamycin resistance. However, high salt growth conditions did increase kanamycin resistance in all three strains.