Regulation of Osmotic Stress by OmpC but not OmpF Increases Kanamycin Resistance in Escherichia coli

Abstract

Changing the ratio of outer membrane proteins, OmpF and OmpC, is a mechanism by which Escherichia coli are able to develop antibiotic resistance. Osmotic stress is known to affect the outer membrane protein ratio by increasing OmpC and decreasing OmpF expression. Our study assessed whether kanamycin resistance under high osmolarity was mediated by an increase in the ratio of OmpC to OmpF. Minimum inhibitory concentration assay for kanamycin and an SDS-PAGE analysis of the outer membrane proteins were performed for wild-type, + TALT12W-1 (Δ omp C), and TALT12W-2 ( omp F ) bacteria grown in media containing varying NaCl concentrations.TALT12W-2 was initially thought to be Δ omp F, but our PCR showed the presence of the ompF gene and the SDS-PAGE analysis also showed OmpF protein expression in the strain. Our results showed an increase in kanamycin resistance with increasing osmotic stress; however, we also saw an increase in resistance comparable to the wild-type cells in the Δ omp C mutants at higher NaCl concentrations. Although we observed an increase in + OmpC protein levels with increasing NaCl concentrations in the wild-type and ompF cells, we did not see a corresponding decrease in OmpF. Taken together, these results suggested that the ratio of OmpC to OmpF plays a role in gaining resistance to antibiotics with the increase in OmpC expression, but may not be the only mechanism conferring resistance.