Investigation of outer membrane porin OmpC mutation mediated relationship between Cefotaxime antibiotic resistance and T4 phage resistance in Escherichia coli

Abstract

Outer membrane porin C (OmpC) is a protein porin found on the outer membrane of Gram-negative bacteria. In Escherichia coli, OmpC allows entry of hydrophilic molecules in to the cell, including cefotaxime (CTX), a cephalosporin antibiotic. Previous research has shown that clinical isolates of multidrug resistant E. coli with mutations in OmpC have increased resistance to cefotaxime. Research has also shown OmpC as a necessary receptor for T4 bacteriophage entry. Due to their mutual dependence on OmpC for entry, we hypothesize that exposure to cefotaxime would select for OmpC mutations that also confer resistance to T4 phage in E. coli BW25113. To test this, we first used a minimum inhibitory concentration (MIC) assay to confirm that deletion of ompC increased E. coli resistance to cefotaxime. With validation of this phenotypic difference, we selected for strains that showed comparable antibiotic resistance to the knockout via sequential passaging of E. coli BW25113 in increasing cefotaxime concentrations. When we subjected these resistant cultures to T4 phage, we saw trends suggesting decreased and delayed lysis as predicted. To confirm that OmpC was indeed the target of selection, we sequenced the ompC gene from these double resistant isolates and found consistent insertion mutations in a number of the isolates. The insertion was predicted to encode an α-helical motif protruding into the channel. This paper addresses the relationship between antibiotics and bacteriophage, an under-researched area in clinical microbiology, and holds implications for how we approach antibiotic therapy and multidrug resistant bacteria.