Mechanisms of quinolone resistance in Escherichia coli: characterization of nfxB and cfxB, two mutant resistance loci decreasing norfloxacin accumulation

Hooper, David C.; Wolfson, John S.; Souza, Karla Teixeira; Ng, Eugene W.M.; McHugh, Gail; Swartz, Morton N.

doi:10.1128/aac.33.3.283

Cited by 116 publications

(90 citation statements)

References 44 publications

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“…Previous work has shown that, independently of soxRS, the soxQl and cfxBl mutations cause transcriptional activation of some of the soxRS regulon genes and the induction of seven other proteins not influenced by soxRS or elevated by oxidative stress (14). Both soxQl and cfxBl, together with the previously identified marRi, map to the 34-min locus on the E. coli chromosome (6,13,14,19), which has been implicated in chromosome-mediated multiple antibiotic resistance (mar) (6,13,16). The soxQl-and the cfxBl-dependent phenotypes do not depend on the soxRS locus, and gene induction by soxRS in response to redox stress does not depend on mar (14).…”

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Repressor mutations in the marRAB operon that activate oxidative stress genes and multiple antibiotic resistance in Escherichia coli

et al. 1994

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Resistance to multiple antibiotics and certain oxidative stress compounds was conferred by three independently selected mutations (marRI, soxQl, and cfxBl) that mapped to 34 min on the Escherichia coli chromosome. Mutations at this locus can activate the marRAB operon, in which marR encodes a putative repressor of mar transcription and marA encodes a putative transcriptional activator of defense genes against antibiotics and oxidants. Overexpression of the wild-type MarR protein reversed the phenotypes (antibiotic resistance and increased antioxidant enzyme synthesis) of all three mutants. DNA sequence analysis showed that, like marRI, the other two mutations were alterations of marR: a 285-bp deletion in cfxBl and a GC--AT transition at codon 70 (Ala-e-Thr) in soxQI. All three mutations cause increased amounts of mar-specific RNA, which supports the hypothesis that MarR has a repressor function in the expression of the marRAB operon. The level of mar RNA was further induced by tetracycline in both the marRI and soxQI strains but not in the cfxBl deletion mutant. In the cfxBl strain, the level of expression of a truncated RNA, with or without tetracycline exposure, was the same as the fully induced level in the other two mutants. Overproduction of MarR in the cfxBl strain repressed the transcription of the truncated RNA and restored transcriptional inducibility by tetracycline. Thus, induction of the marRAB operon results from the relief of the repression exerted by MarR. The marRAB operon evidently activates both antibiotic resistance and oxidative stress genes.

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Repressor mutations in the marRAB operon that activate oxidative stress genes and multiple antibiotic resistance in Escherichia coli

et al. 1994

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“…In this second type of resistance, accumulation of the antibiotic within the cell may be diminished by reduced uptake or by increased efflux from the cell (33). These low-level broad resistances are usually mediated by chromosomal mutations (15,19,23,39), but few are well characterized either as regulatory systems or for the cellular mechanisms involved.…”

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Activation of multiple antibiotic resistance and binding of stress-inducible promoters by Escherichia coli Rob protein

et al. 1995

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Multiple antibiotic resistance in Escherichia coli can be mediated by induction of the SoxS or MarA protein, triggered by oxygen radicals (in the soxRS regulon) or certain antibiotics (in the marRAB regulon), respectively. These small proteins (SoxS, 107 residues; MarA, 127 residues) are homologous to the C terminus of the XylS-AraC family of proteins and are more closely related to a ϳ100-residue segment in the N terminus of Rob protein, which binds the right arm of the replication origin, oriC. We investigated whether the SoxS-MarA homology in Rob might extend to the regulation of some of the same inducible genes. Overexpression of Rob indeed conferred multiple antibiotic resistance similar to that known for SoxS and MarA (against chloramphenicol, tetracycline, nalidixic acid, and puromycin), as well as resistance to the superoxide-generating compound phenazine methosulfate. The Rob-induced antibiotic resistance depended only partially on the micF antisense RNA that down-regulates the OmpF outer membrane porin to limit antibiotic uptake. Similar antibiotic resistance was conferred by expression of a Rob fragment containing only the N-terminal 123 residues that constitute the SoxS-MarA homology. Both intact Rob and the N-terminal fragment activated expression of stress genes (inaA, fumC, sodA) but with a pattern distinct from that found for SoxS and MarA. Purified Rob protein bound a DNA fragment containing the micF promoter (50% bound at ϳ10 ؊9 M Rob) as strongly as it did oriC, and it bound more weakly to DNA containing the sodA, nfo, or zwf promoter (50% bound at 10 ؊8 to 10 ؊7 M). Rob formed multiple DNA-protein complexes with these fragments, as seen previously for SoxS. These data point to a DNA-binding gene activator module used in different protein contexts.

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“…A number of reports regarding chromosomal mutations that confer low-level resistance to a variety of antibiotics (10,14,19,29) have appeared. In most cases, however, little is known about either the identity of the gene designated by the resistance mutation or the cellular mechanisms affected by these mutations.…”

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Overexpression of the MarA positive regulator is sufficient to confer multiple antibiotic resistance in Escherichia coli

Gambino¹,

Gracheck²,

Miller³

1993

J Bacteriol

122

145

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A genetic approach was undertaken to identify normal bacterial genes whose products function to limit the effective concentration of antibiotics. In this approach, a multicopy plasmid library containing cloned Escherichia coli chromosomal sequences was screened for transformants that showed increased resistance to a number of unrelated antibiotics. Three such plasmids were identified, and all contained sequences originating from the mar locus. DNA sequence analysis of the minimal complementation unit revealed that the resistance phenotype was associated with the presence of the marA gene on the plasmids. The putative marA gene product is predicted to contain a helix-turn-helix DNA binding domain that is very similar to analogous domains found in three other E. coli proteins. One such similarity was to the SoxS gene product, the elevated expression of which has previously been associated with the multiple antibiotic resistance (Mar) phenotype. Constitutive expression of marA conferred antibiotic resistance even in cells carrying a deletion of the chromosomal mar locus. We have also found that transformants bearing marA plasmids show a significant reduction in ompF translation but not transcription, similar to previously described mar mutants. However, this reduction in ompF expression plays only a minor role in the resistance mechanism, suggesting that functions encoded by genes unlinked to mar must be affected by marA. These results suggest that activation of marA is the ultimate event that occurs at the mar locus during the process that results in multiple antibiotic resistance.

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Mechanisms of quinolone resistance in Escherichia coli: characterization of nfxB and cfxB, two mutant resistance loci decreasing norfloxacin accumulation

Cited by 116 publications

References 44 publications

Repressor mutations in the marRAB operon that activate oxidative stress genes and multiple antibiotic resistance in Escherichia coli

Repressor mutations in the marRAB operon that activate oxidative stress genes and multiple antibiotic resistance in Escherichia coli

Activation of multiple antibiotic resistance and binding of stress-inducible promoters by Escherichia coli Rob protein

Overexpression of the MarA positive regulator is sufficient to confer multiple antibiotic resistance in Escherichia coli

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