Knockout of OmpF and OmpC does not affect kanamycin susceptibility in two different strains of Escherichia coli K-12

OmpF and OmpC are key outer membrane diffusion porins in Escherichia coli. Previous studies have tested OmpF and OmpC mutants for resistance to the antibiotic kanamycin, with conflicting results. We set out to determine if the inconsistent results were due to the different E. coli K-12 strains employed by each study. Side by side minimum inhibitory concentration (MIC) assays were conducted to test kanamycin resistance of OmpF and OmpC mutants from 2 different E. coli genetic backgrounds. We observed no change in kanamycin resistance in the OmpF and OmpC mutants in either genetic backgrounds tested. Based on these results, we conclude that OmpF and OmpC play no role in kanamycin resistance in E. coli K-12. The genetic basis of the ompF deletion in E. coli strain JF700 had yet to be characterized in literature. We uncovered a 1195 bp IS5 transposon insertion within the ompF gene using Sanger sequencing. This insertion explains the lack of OmpF protein expression in this mutant.