Identification for mar mutants among quinolone-resistant clinical isolates of Escherichia coli

Abstract

Quinolone-resistant clinical Escherichia coli isolates were examined for mutations in the marRAB operon of the multiple antibiotic resistance (mar) locus. Among 23 strains evaluated, 8 were chosen for further study: 3 that showed relatively high levels of uninduced, i.e., constitutive, expression of the operon and 5 with variable responses to induction by salicylate or tetracyclines. The marR genes, specifying the repressor of the operon, cloned from the three strains constitutively expressing the operon did not reduce the level of expression of beta-galactosidase from a marO::lacZ transcriptional fusion and were therefore mutant; however, marR genes cloned from the five other clinical strains repressed LacZ expression and were wild type. All three mutant marR genes contained more than one mutation: a deletion and a point mutation. Inactivation of the mar locus in the three known marR mutant strains with a kanamycin resistance cassette introduced by homologous recombination reduced resistance to quinolones and multiple antibiotics. These findings indicate that mar operon mutations exist in quinolone-resistant clinical E. coli isolates and contribute to quinolone and multidrug resistance.

Adaptive Laboratory Evolution of Antibiotic Resistance Using Different Selection Regimes Lead to Similar Phenotypes and Genotypes

“…Mutations in acrR as well as in marR and rob , also identified to be mutated in the increment strains adapted to PIP, lead to the multiple antibiotic resistance (mar) phenotype, which was described to confer resistance toward a variety of drugs including beta-lactam antibiotics and tetracyclines. This finding explains the cross-resistance observed for TET and PIP evolved lineages in this experiment (George and Levy, 1983; Cohen et al, 1989; Ariza et al, 1995; Maneewannakul and Levy, 1996; Oethinger et al, 1998). The lack of mutations in marR and rob in the gradient adapted strains might account for the difference in cross-resistance toward TET compared to the 25% increment adapted strains.…”

Genomics of Rapid Adaptation to Antibiotics: Convergent Evolution and Scalable Sequence Amplification

“…Four additional genes likely influence regulation of acrAB ( acrR , marR , lon , and possibly ycbZ ; fig. 4 [Seoane and Levy 1995; Ma et al 1996; Maneewannakul and Levy 1996; Barbosa and Levy 2000; Nicoloff et al 2006]). Moreover, two of the four genes ( marR and ycbZ ) are affected by a particularly high number of mutational changes, further emphasizing their possible adaptive value.…”

Escherichia coli mar and acrAB Mutants Display No Tolerance to Simple Alcohols

“…E. coli AG100 (K-12 argE3 thi-1 rpsL xyl mtl Δ( gal-uvrB ) supE44 ) [27], AG112 ( marR 5-bp deletion) [28], AG100A (Δ( acrAB )::Kan) [19], AG102K ( marR Δ( acrAB )::Kan) [19] and AG100/Kan (Δ( marCORAB )::Kan) [29] were all kindly donated by Dr. S. B. Levy, Center for Adaptation Genetics and Drug Resistance, Tufts University School of Medicine, Boston MA, USA.…”