Cross-resistance to fluoroquinolones in multiple-antibiotic-resistant (Mar) Escherichia coli selected by tetracycline or chloramphenicol: decreased drug accumulation associated with membrane changes in addition to OmpF reduction

Abstract

Chromosomal multiple-antibiotic-resistant (Mar) mutants of Escherichia coli, selected on agar containing low concentrations of tetracycline or chloramphenicol, were 6-to 18-fold less susceptible to the fluoroquinolones than were their wild-type E. coli K-12 or E. coli C parental strains. The frequency of emergence of such mutants was at least 1,000-fold higher than that of those selected by the fluoroquinolone norfloxacin directly. When Mar mutants, but not wild-type cells, were plated on norfloxacin, mutants resistant to high levels of norfloxacin (2 ,ug/ml) appeared at a relatively high (-10-7) frequency. In addition to decreased amounts of OmpF, Mar mutants had other outer membrane protein changes and were four-to eightfold less susceptible to fluoroquinolones than was an ompF::Tn5 mutant lacking only OmpF. Accumulation of [3H]norfloxacin was more than threefold lower in the Mar mutants than in wild-type cells and twofold lower than in the OmpF-deficient derivative. These differences were not attributable to a change in the endogenous active efflux system for norfloxacin in E. coli. Norfloxacin-induced inhibition of DNA synthesis was threefold lower in intact cells of a Mar mutant than in susceptible cells, but this difference was not seen in toluene-permeabilized cells. Insertion of TnS into marA (min 34.05 on the chromosome) led to a return of the wild-type patterns of norfloxacin accumulation, fluoroquinolone and other antimicrobial agent susceptibilities, and outer membrane protein profile, including partial restoration of OmpF. These findings together suggest that marA-dependent fluoroquinolone resistance is linked to decreased cell permeability, only part of which can be accounted for by the reduction in OmpF. Once mutated to marA, cells can achieve high levels of quinolone resistance at a relatively high frequency.

Characterization of a cationic surfactant-resistant mutant isolated spontaneously from Escherichia coli

“…Such a pleiotropic mutation in a regulatory gene causing multi-drug resistance has been reported in mar mutants of E. coli (Cohen et al 1989(Cohen et al , 1993. In these mutants, both reduction of the outer membrane permeability and suppression of OmpF synthesis were observed, as in strain OW66 described in this study.…”

“…It is known that permeability to antimicrobial agents, especially to small hydrophilic agents, through the outer membrane in E. coli greatly depends on the contents of OmpF and OmpC porin proteins, and that OmpF deficiency makes cells resistant to some antibiotics (Harder et al 1981;Cohen et al 1989;Ariza et al 1995;Thanassi et al 1995). The finding that the content of OmpF in strain OW66 was lower than that of strain OW6, even in the absence of CTAB, strongly suggests dependency of the resistance of the mutant on the OmpF level in the outer membrane.…”

Genotype-by-Environment Interactions Influencing the Emergence of rpoS Mutations in Escherichia coli Populations

“…Resistance to antibiotics is not a known role for RpoS so the argument above-that mutations are less selected when RpoS is needed in stress resistance-does not hold readily. However, previous studies have shown that the major outer membrane porin through which chloramphenicol transverses in E. coli is OmpF (Harder et al 1981;Cohen et al 1988Cohen et al , 1989. RpoS negatively influences ompF transcription (Liu and Ferenci 2001); therefore loss of RpoS would be a disadvantage as high outer membrane permeability to antibiotics would be a liability and hence provide an indirect F sp contribution.…”

Tetracyclines in veterinary medicine and bacterial resistance to them

“…the presence of tetracycline in the environment), generally when the overproduction of the global activator protein MarA is induced (Hachler et al, 1991). In addition to the positive regulation of the acrAB operon, the MarA protein down-regulates the synthesis of the major porin OmpF, through the increased production of the antisense RNA, encoded by micF and that leads to the decreased accumulation of tetracycline (Cohen et al, 1988(Cohen et al, , 1989.…”