Plasmid-mediated qnr genes provide only a modest decrease in quinolone susceptibility but facilitate the selection of higher-level resistance. In Escherichia coli strain J53 without qnr, ...ciprofloxacin resistance often involves mutations in the GyrA subunit of DNA gyrase. Mutations in gyrA were absent, however, when 43 mutants with decreased ciprofloxacin susceptibility were selected from J53(pMG252) with qnrA1. Instead, in 13 mutants, individual and whole-genome sequencing identified mutations in marR and soxR associated with increased expression of marA and soxS and, through them, increased expression of the AcrAB pump, which effluxes quinolones. Nine mutants had increased expression of the MdtE efflux pump, and six demonstrated increased expression of the ydhE pump gene. Many efflux mutants also had increased resistance to novobiocin, another pump substrate, but other mutants were novobiocin hypersusceptible. Mutations in rfaD and rfaE in the pathway for inner core lipopolysaccharide (LPS) biosynthesis were identified in five such strains. Many of the pump and LPS mutants had decreased expression of OmpF, the major porin channel for ciprofloxacin entry. Three mutants had increased expression of qnrA that persisted when pMG252 from these strains was outcrossed. gyrA mutations were also rare when mutants with decreased ciprofloxacin susceptibility were selected from E. coli J53 with aac(6')-Ib-cr or qepA. We suggest that multiple genes conferring low-level resistance contribute to enhanced ciprofloxacin resistance selected from an E. coli strain carrying qnrA1, aac(6')-Ib-cr, or qepA because these determinants decrease the effective ciprofloxacin concentration and allow more common but lower-resistance mutations than those in gyrA to predominate.
The Qnr pentapeptide repeat proteins interact with DNA gyrase and protect it from quinolone inhibition. The two external loops, particularly the larger loop B, of Qnr proteins are essential for ...quinolone protection of DNA gyrase. The specific QnrB1 interaction sites on DNA gyrase are not known. In this study, we investigated the interaction between GyrA and QnrB1 using site-specific photo-cross-linking of QnrB1 loop B combined with mass spectrometry. We found that amino acid residues 286 to 298 on the tower domain of GyrA interact with QnrB1 and play a key role in QnrB1 protection of gyrase from quinolone inhibition. Alanine replacement of arginine at residue 293 and a small deletion of amino acids 286 to 289 of GyrA resulted in a decrease in the QnrB1-mediated increase in quinolone MICs and also abolished the QnrB1 protection of purified DNA gyrase from ciprofloxacin inhibition.
Consensus on β-Lactamase Nomenclature Bradford, Patricia A; Bonomo, Robert A; Bush, Karen ...
Antimicrobial agents and chemotherapy,
04/2022, Letnik:
66, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Assigning names to β-lactamase variants has been inconsistent and has led to confusion in the published literature. The common availability of whole genome sequencing has resulted in an exponential ...growth in the number of new β-lactamase genes. In November 2021 an international group of β-lactamase experts met virtually to develop a consensus for the way naturally-occurring β-lactamase genes should be named. This document formalizes the process for naming novel β-lactamases, followed by their subsequent publication.
Qnr is a plasmid-encoded and chromosomally determined protein that protects DNA gyrase and topoisomerase IV from inhibition by quinolones. Despite its prevalence worldwide and existence prior to the ...discovery of quinolones, its native function is not known. Other synthetic compounds and natural products also target bacterial topoisomerases. A number were studied as molecular probes to gain insight into how Qnr acts. Qnr blocked inhibition by synthetic compounds with somewhat quinolone-like structure that target the GyrA subunit, such as the 2-pyridone ABT-719, the quinazoline-2,4-dione PD 0305970, and the spiropyrimidinetrione pyrazinyl-alkynyl-tetrahydroquinoline (PAT), indicating that Qnr is not strictly quinolone specific, but Qnr did not protect against GyrA-targeting simocyclinone D8 despite evidence that both simocyclinone D8 and Qnr affect DNA binding to gyrase. Qnr did not affect the activity of tricyclic pyrimidoindole or pyrazolopyridones, synthetic inhibitors of the GyrB subunit, or nonsynthetic GyrB inhibitors, such as coumermycin A1, novobiocin, gyramide A, or microcin B17.Thus, in this set of compounds the protective activity of Qnr was confined to those that, like quinolones, trap gyrase on DNA in cleaved complexes.
Bacteria can mutate to acquire quinolone resistance by target alterations or diminished drug accumulation. Plasmid-mediated resistance to quinolones in clinical isolates has been claimed but not ...confirmed. We investigated whether a multiresistance plasmid could transfer resistance to quinolones between bacteria.
We transferred resistance between strains by conjugation. The resistance plasmid was visualised in different hosts by agarose-gel electrophoresis. We determined the frequency of spontaneous mutations to ciprofloxacin or nalidixic-acid resistance in
Escherichia coli strains, with or without the quinolone resistance plasmid.
A multiresistance plasmid (pMG252) from a clinical isolate of
Klebsiella pneumoniae was found to increase quinolone resistance to minimum inhibitory concentrations (MICs) as high as 32 μg/mL for ciprofloxacin when transferred to strains of
K pneumoniae deficient in outer-membrane porins. Much lower resistance was seen when pMG252 was introduced into
K pneumoniae or
E coli strains with normal porins. The plasmid had a wide host range and expressed quinolone resistance in other enterobacteriaceae and in
Pseudomonas aeruginosa. From a plasmid-containing
E coli strain with ciprofloxacin MIC of 0·25 μg/mL and nalidixic-acid MIC of 32 μg/mL, quinolone-resistant mutants could be obtained at more than 100 times the frequency of a plasmid-free strain, reaching MICs for ciprofloxacin of 4 μg/mL and for nalidixic acid of 256 μg/mL.
Transferable resistance to fluoroquinines and nalidixic acid has been found in a clinical isolate of
K pneumoniae on a broad host range plasmid. Although resistance was low in wild-type strains, higher levels of quinolone resistance arose readily by mutation. Such a plasmid can speed the development and spread of resistance to these valuable antimicrobial agents.
genes are found in aquatic bacteria and preceded the development of synthetic quinolones. Their natural functions are unknown. We evaluated the expression of chromosomal
in
species in response to ...environmental stresses and DNA damaging agents. Sub-inhibitory concentrations of quinolones, but not other DNA damaging agents, induced the expression of chromosomal
by more than five times in
and
Cold shock also induced the expression of
in
and
as well as
in
induction by cold shock was not altered in Δ
or Δ
mutants or in a strain over-expressing
, that otherwise directly modulate
induction by ciprofloxacin. In contrast,
induction by cold shock was reduced in a Δ
mutant in the cold shock regulon compared to the wild type. In conclusion, cold shock as well as quinolones induce chromosomal
in
species, and the related
in
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