Genetics and regulation of outer membrane protein expression by quinolone resistance loci nfxB, nfxC, and cfxB.

Quinolone resistance mutations (cfxB1, marA1, and soxQ1) that reduce porin outer membrane protein OmpF map near 34 min on the Escherichia coli chromosome. Another such mutation, nfxC1, was found in strain KF131 (nfxB, 19 min). nfxC1 and cfxB1 mutants (selected with quinolones) differed slightly but reproducibly from marA1 (selected with tetracycline) and soxQ1 (selected with menadione) mutants in quinolone resistance and linkage to zdd2208::Tn10kan (33.7 min). For nfxB nfxC1 and cfxB1 mutants, as previously shown for marA mutants, resistance and reduced OmpF required the micF locus encoding an antisense RNA complementary to ompF mRNA and were associated with increased micF expression.