Quinolone susceptibility and genetic characterization of Salmonella enterica subsp. enterica isolated from pet turtles / 한국실험동물학회지

Turtle-borne Salmonella enterica owns significance as a leading cause in human salmonellosis. The current study aimed to determine the quinolone susceptibility and the genetic characteristics of 21 strains of S. enterica subsp. enterica isolated from pet turtles. Susceptibility of four antimicrobials including nalidixic acid, ciprofloxacin, ofloxacin, and levofloxacin was examined in disk diffusion and MIC tests where the majority of the isolates were susceptible to all tested quinolones. In genetic characterization, none of the isolates were positive for qnr or aac(6')-Ib genes and no any target site mutations could be detected in gyrA, gyrB, and parC quinolone resistance determining regions (QRDR). In addition, neighbor-joining phylogenetic tree derived using gyrA gene sequences exhibited two distinct clads comprising; first, current study isolates, and second, quinolone-resistant isolates of human and animal origin. All results suggest that studied strains of S. enterica subsp. enterica isolated from pet turtles are susceptible to quinolones and genetically more conserved with regards to gyrA gene region.

Determinants of quinolone resistance in Escherichia coli causing community-acquired urinary tract infection in Bejaia, Algeria

OBJECTIVE@#To investigate the mechanisms of quinolone resistance and the association with other resistance markers among Esherichia coli (E. coli) strains isolated from outpatient with urinary tract infection in north of Algeria.@*METHODS@#A total of 30 nalidixic acid-resistant E. coli isolates from outpatient with urinary tract infections from January 2010 to April 2011 in north of Algeria (Bejaia) were studied. Antimicrobial susceptibility was determined by disc diffusion assay, minimal inhibitory concentrations (MIC) of quinolone were determined by microdilution. Mutations in the Quinolone Resistance-Determining Region (QRDR) of gyrA and parC genes and screening for qnr (A, B and S) and bla genes were done by PCR and DNA sequencing.@*RESULTS@#Most of the E. coli isolates (56.66%) were shown to carry mutations in gyrA and parC (gyrA: Ser83Leu + Asp87Asn and parC:Ser80Ile). While, 16.66% had only an alteration in gyrA: Ser83Leu. One isolate produced qnrB-like and two qnrS-like. Four isolates were CTX-M-15 producers associated with TEM-1 producing in one case. Co-expression of blaCTX-M-15 and qnrB was determined in one E. coli isolate.@*CONCLUSIONS@#Our findings suggested the community emergence of gyrA and parC alterations and Qnr determinants that contributed to the development and spread of fluoroquinolone resistance in Algerian E. coli isolates.

Screening of quinolone resistance determinants in ciprofloxacin-resistant Acinetobact-er baumannii isolates / 军事医学

Objective To investigate the quinolone resistance determinants in ciprofloxacin-resistant Acinetobacter bau-mannii (ABA)clinical isolates.Methods One hundred and fourteen ciprofloxacin-resistant ABA strains were collected from six Chinese hospitals .The quinolone resistance determining region ( QRDR) of 4 target genes ( gyrA, gyrB, parC and parE) was amplified , sequenced and compared with the reference genome of ATCC 17978 to identify possible resistance-related mutations.Nine plasmid-mediated quinolone resistance (PMQR) genes (qnrA, qnrB, qnrC, qnrD, qnrS, qepA, aac(6′)-Ⅰb-cr, oqxA and oqxB) were also amplified, and the amplicons were then sequenced to determine their character-istics.Results Almost all isolates (113/114, 99.1%) harbored a substitution in codon 83 of gyrA gene, leading to a Ser83Leu mutation.Meanwhile,58.8%(67/114) of the isolates possessed dual mutations of GyrA-Ser83Leu and GyrA-Ser80Leu, which were known determinants for ciprofloxacin resistance .There were also multiple non-synonymous substitu-tions in gyrB, leading to Arg393Ser, Arg393Cys, Thr401Ala, Pro406Ser, Val430Phe, Cys440Ser and Gly480Arg muta-tions with prevalence rates of 95.6%, 0.9%, 96.5%, 96.5%, 100%, 96.5%and 96.5%,respectively.For parE, all the seven mutations were synonymous and found in more than 96%of the tested isolates.For PMQR genes, although 83.3%(95/114) of the isolates were positive for aac(6′)-Ⅰb, nocrmutations were identified.None of the other eight PMDR genes were found in our strain collection .Conclusion Although multiple mutations are identified in gyrB and parE, these mutations might be the characteristic SNP markers for specific clones , unlikely linked to quinolone resistance .No PMQR is found in the tested isolates.Mutations in chromosomal QRDR (GyrA-Ser83Leu and ParC-Ser80Leu) are the main determi-nants of ciprofloxacin resistance in our ABA collection .

Plasmid-mediated quinolone resistance (PMQR) and mutations in the topoisomerase genes of Salmonella enterica strains from Brazil

The objective of this study was to identify mutations in the Quinolone Resistance Determining sources Regions (QRDR) of the gyrA, gyrB, parC, and parE genes and to determine if any of the qnr variants or the aac(6')-Ib-cr variant were present in strains of Salmonella spp. isolated in Brazil. A total of 126 Salmonella spp. strains from epidemic (n = 114) and poultry (n = 12) origin were evaluated. One hundred and twelve strains (88.8%) were resistant to nalidixic acid (NAL) and 29 (23.01%) showed a reduced susceptibility to ciprofloxacin (Cip). The mutations identified were substitutions limited to the QRDR of the gyrA gene in the codons for Serine 83, Aspartate 87 and Alanine 131. The sensitivity to NAL seems to be a good phenotypic indication of distinguishing mutated and nonmutated strains in the QRDR, however the double mutation in gyrA did not cause resistance to ciprofloxacin. The qnrA1 and qnrB19 genes were detected, respectively, in one epidemic strain of S. Enteritidis and one strain of S. Corvallis of poultry origin. Despite previous detection of qnr genes in Brazil, this is the first report of qnr gene detection in Salmonella, and also the first detection of qnrB19 gene in this country. The results alert for the continuous monitoring of quinolone resistance determinants in order to minimize the emergence and selection of Salmonella spp. strains showing reduced susceptibility or resistance to quinolones.

QRDR mutations, efflux system & antimicrobial resistance genes in enterotoxigenic Escherichia coli isolated from an outbreak of diarrhoea in Ahmedabad, India.

Background & objectives: Diverse mechanisms have been identified in enteric bacteria for their adaptation and survival against multiple classes of antimicrobial agents. Resistance of bacteria to the most effective fluoroquinolones have increasingly been reported in many countries. We have identified that most of the enterotoxigenic Escherichia coli (ETEC) were resistant to several antimicrobials in a diarrhoea outbreak at Ahmedabad during 2000. The present study was done to identify several genes responsible for antimicrobial resistance and mobile genetic elements in the ETEC strains. Methods: Seventeen ETEC strains isolated from diarrhoeal patients were included in this study. The antimicrobial resistance was confirmed by conventional disc diffusion method. PCR and DNA sequencing were performed for the identification of mutation in the quinolone resistance-determining regions (QRDRs). Efflux pump was tested by inhibiting the proton-motive force. DNA hybridization assay was made for the detection of integrase genes and the resistance gene cassettes were identified by direct sequencing of the PCR amplicons. Results: Majority of the ETEC had GyrA mutations at codons 83 and 87 and in ParC at codon 80. Six strains had an additional mutation in ParC at codon 108 and two had at position 84. Plasmid-borne qnr gene alleles that encode quinolone resistance were not detected but the newly described aac(6’)-Ib-cr gene encoding a fluoroquinolne-modifying enzyme was detected in 64.7 per cent of the ETEC. Class 1 (intI1) and class 2 (intI2) integrons were detected in six (35.3%) and three (17.6%) strains, respectively. Four strains (23.5%) had both the classes of integrons. Sequence analysis revealed presence of dfrA17, aadA1, aadA5 in class 1, and dfrA1, sat1, aadA1 in class 2 integrons. In addition, the other resistance genes such as tet gene alleles (94.1%), catAI (70.6%), strA (58.8%), blaTEM-1(35.2%), and aphA1-Ia (29.4%) were detected in most of the strains. Interpretation & conclusions: Innate gene mutations and acquisition of multidrug resistance genes through mobile genetic elements might have contributed to the emergence of multidrug resistance (MDR) in ETEC. This study reinforces the necessity of utilizing molecular techniques in the epidemiological studies to understand the nature of resistance responsible for antimicrobial resistance in different species of pathogenic bacteria.

Detection of quinolone-resistance mutations in Salmonella spp. strains of epidemic and poultry origin

Mutations into codons Aspartate-87 (62 percent) and Serine-83 (38 percent) in QRDR of gyrA were identified in 105 Salmonella strains resistant to nalidixic acid (94 epidemic and 11 of poultry origin). The results show a high incidence of mutations associated to quinolone resistance but suggest association with others mechanisms of resistance.

Chromosomal Mutations in oprD, gyrA, and parC in Carbapenem Resistant Pseudomonas aeruginosa / 대한임상미생물학회지

BACKGROUND: Outbreaks of carbapenem resistant P. aeruginosa give rise to significant therapeutic challenges for treating nosocomial infections. In this study, we analyzed carbapenem resistance mechanisms in carbapenem resistant and clonally different P. aeruginosa strains. We analyzed chromosomal alterations in the genes of OprD and efflux system regulatory proteins (MexR, NalC, NalD, MexT, and MexZ). We also investigated chromosomal alterations in the quinolone resistance-determining region (QRDR) for quinolone resistance mechanisms. METHODS: Twenty-one clonally different P. aeruginosa strains were isolated by repetitive extragenic palindromic sequence-based PCR (rep-PCR). PCR and DNA sequencing were conducted for the detection of beta-lactamase genes and chromosomal alterations of efflux pump regulatory genes, oprD, and QRDR in gyrA, gyrB, parC, and parE. RESULTS: Only one (P28) of the 21 strains harbored bla VIM-2. Two isolates had mutations in nalD or mexZ that were associated with efflux pump overexpression. Chromosomal alterations causing loss of OprD were found in 4 out of 21 carbapenem resistant P. aeruginosa strains. Nine of 10 imipenem and ciprofloxacin resistant strains had alterations in gyrA and/or parC. CONCLUSION: Carbapenem resistance in P. aeruginosa was mediated by several mechanisms, including loss of the OprD, overexpression of efflux systems, and production of carbapenemase. Resistance to quinolone is frequently caused by point mutations in gyrA and/or parC.

Comparison of QRDR Mutations in Fluoroquinolone-resistant Klebsiella pneumoniae Between Fluoroquinolone Inducing Strains in vitro and Clinical Isolates / 中华医院感染学杂志

OBJECTIVE To study the differences of quinolones-resistant determining region(QRDR) in DNA gyrase A(gyrA) subunit between drug-resistant Klebsiella pneumoniae induced by fluoroquinolone in vitro and strains isolated from clinical isolates.Furthermore,to reveal the relation between different QRDR gene mutations and drug-resistance. METHODS Ten sensitive K.pneumoniae strains were selected and induced into drug-resistant strains by ciprofloxacin.The QRDR in gyrA by polymerase chain reaction(PCR) was amplified and compared their DNA sequences with clinically isolated quinolone-resistant K.pneumoniae. RESULTS We had found several gene mutations of QRDR in fluoroquinolone-resistant K.pneumoniae induced by ciprofloxacin,including Ser 83(TCC)→Phe(TTC) and Ile(ATC);and Gln106(CAG)→Leu(CTG).And the alteration of Gln106(CAG)→Leu(CTG) was a new discovery. CONCLUSIONS There are gene mutations of QRDR in fluoroquinolone-resistant K.pneumoniae induced by ciprofloxacin.The mutation of Ser 83(TCC) and Gln106(CAG) is probably the molecular basis of inducing drug-resistant strains.

A mutation in QRDR in the ParC subunit of topoisomerase IV was responsible for fluoroquinolone resistance in clinical isolates of Streptococcus pneumoniae

Forty-one strains of Streptococcus pneumoniae were isolated at Seoul National University Children's Hospital from 1991 to 1997. Isolates were divided into six groups based on MICs of three quinolones, ciprofloxacin, ofloxacin and norfloxacin. Sequencing showed that the isolates which were intermediately resistant to three quinolones or resistant to at least one kind of quinolone had one missense mutation, Lys137-->Asn(AAG-->AAT) substitution in the ParC subunit of topoisomerase IV without additional mutation in QRDR of the GyrA subunit of DNA gyrase. In conclusion, the ParC subunit of DNA topoisomerase IV is the primary target site for fluoroquinolone in S. pneumoniae and Lys137-->Asn substitution renders the quinolone resistance in S. pneumoniae.