JAC Advance Access published online on September 30, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn406
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Original research |
Prevalence and distribution of plasmid-mediated quinolone resistance genes in clinical isolates of Escherichia coli lacking extended-spectrum β-lactamases
1 Department of Microbiology, Shrewsbury and Telford NHS Trust, Mytton Oak Road, Shrewsbury SY3 8XQ, UK 2 Department of Medical Microbiology, School of Medicine, University of Manchester, Clinical Sciences Building 1, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, UK
* Correspondence address. Department of Microbiology, Royal Shrewsbury Hospital, Shrewsbury SY3 8XQ, UK. Tel: +44-1743-261161; Fax: +44-1743-261165; E-mail: rod.warren{at}sath.nhs.uk
Received 30 May 2008; returned 7 July 2008; revised 2 September 2008; accepted 3 September 2008
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Abstract |
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Objectives: The aac(6')-Ib-cr gene has been described in plasmids from CTX-M-15-producing Escherichia coli in the worldwide ST131 lineage, but has not been systematically sought in other quinolone-resistant strains in the UK. A rise in quinolone resistance in bacteraemia isolates in the UK preceded the increased prevalence of CTX-M-producing strains. This study aimed to describe the presence of plasmid-encoded quinolone resistance genes in historical and current strains of E. coli not producing extended-spectrum β-lactamases (ESBLs).
Methods: Ciprofloxacin-resistant, non-ESBL-producing E. coli isolates included nationally distributed isolates from the BSAC UK bacteraemia surveillance programme between 2001 and 2005, urinary isolates from a regional project in 2000 and local strains in 2006. The aac(6')-Ib-cr gene was detected using PCR followed by restriction fragment length polymorphism analysis. Multiplex PCR was used to detect qnr genes. Isolates with aac(6')-Ib-cr were assessed for aminoglycoside susceptibilities and were serotyped.
Results: The prevalence of the aac(6')-Ib-cr gene was 3% and 9% in current local urinary and historic national bacteraemia quinolone-resistant non-ESBL-producing E. coli, respectively. Of 521 regional urinary E. coli isolates from 2000, 14 were norfloxacin-resistant, none of which carried the aac(6')-Ib-cr gene. National positive bacteraemia isolates from 2001/2 were type O102-ST405 and, in 2004/5, types O1-ST645 and O25-ST131. Positive local urinary isolates from 2006 included serotypes O1 and O25.
Conclusions: In the UK, aac(6')-Ib-cr occurs in E. coli in the absence of CTX-M-15, but with a restricted serotype distribution. Its presence in widespread bacteraemia isolates of a single type from 2001 to 2002, prior to the spread of CTX-M-15 in Britain, might suggest a lineage from which plasmid recombination occurred in man or other species.
Key Words: qnr , aac(6')-Ib , ESBLs
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Introduction |
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In 1998, the first transferable plasmid-encoded quinolone resistance gene qnr was isolated from a clinical isolate of ciprofloxacin-resistant Klebsiella pneumoniae.1 The introduction of a plasmid (pMG252) with this gene to other isolates of Escherichia coli produced a modest (4–16-fold) loss of susceptibility to a wide range of fluoroquinolones within the susceptible range (i.e. MIC of ciprofloxacin, 0.25 mg/L). This original qnrA gene product (belonging to the pentapeptide repeat family), which protects DNA gyrase from inhibition by ciprofloxacin, has been joined by qnrB and qnrS, related proteins with a similar effect.2–4
Clinical isolates of E. coli carrying qnrA-containing plasmids collected from Shanghai between 2000 and 2001 were found to be four times less susceptible in vitro to quinolones than previously expected (1 mg/L), which is a level of clinical resistance.5 Neither increased copy number nor amplified expression of qnrA contributed to the higher level of resistance; therefore, random transposon insertion was used to knock out the gene responsible for the increased resistance generated by these plasmids.6 The gene found to be responsible encoded an aminoglycoside acetyltransferase [aac(6')-Ib], which typically confers resistance to tobramycin and amikacin, but not to gentamicin.6 Sequencing of the aac(6')-Ib gene found on the plasmid in question revealed two codon changes. This newly identified bifunctional enzyme acetylated the aminoglycosides, ciprofloxacin and norfloxacin, but not moxifloxacin or levofloxacin, and was designated aac(6')-Ib-cr.
This enzyme was described from China in 20066 and subsequently identified in earlier Canadian strains.7 In the USA,8 the aac(6')-Ib-cr gene was detected in 15 of 47 (32%) isolates of ceftazidime-resistant E. coli (not specified as clavulanate-enhanced or indifferent), with ciprofloxacin MICs of 
0.25 mg/L. All these strains had a ciprofloxacin MIC of >1 mg/L, and 13/31 (42%) were gentamicin-resistant compared with 2/16 (12%) strains without aac(6')-Ib-cr. Rates were stable from 1999 onwards and were not associated with qnr genes, but there is no information on the prevalence in E. coli in the absence of extended-spectrum β-lactamases (ESBLs) or the sequence lineage. Robicsek et al.6 found that 51% of the E. coli in Shanghai carried aac(6')-Ib-cr. Subsequent analysis of strains from six Chinese provinces between 1998 and 2002 suggests that 9.9% of ESBL-producing E. coli carry aac(6')-Ib-cr.9
CTX-M enzymes have become the most prevalent ESBLs.10 The pandemic of CTX-M ESBLs in E. coli in many countries has been accompanied by coincident quinolone resistance. The CTX-M-15-producing strain E. coli clone ST131 serotype O25, defined by multilocus sequence typing (MLST), has been recorded from many countries11 and often produces aac(6')-Ib-cr, which is normally present with other resistance genes on an F11 plasmid. Such CTX-M-producing strains suddenly became prevalent in a multicentric fashion in the UK and Canada over the period 2002–03, appearing locally in February 2003.12 A report on strains from Calgary, Canada suggests that in 2004 only 4 of 139 (2.9%) ciprofloxacin- or tobramycin-resistant E. coli carried aac(6')-Ib-cr without CTX-M-15, whereas in 2007, this had risen to 21/346 (6.1%) isolates.13 In this study, CTX-M-15-producing isolates increased from 2/139 (1.4%) to 32/346 (9.2%) cases. Quinolone resistance in bacteraemic E. coli in the UK was described as increasing from 2.1% to 6.5% prior to the arrival of CTX-M-15 in the immediately preceding period, 1995–2001.14 It has been suggested that genes such as aac(6')-Ib-cr and qnr allow the survival of strains prior to GyrA mutation, permitting the emergence of high-level quinolone resistance.6 If this was the case, such genes, then unrecognized, might have been prevalent prior to the arrival of CTX-M-15.
Few culture collections from the period immediately preceding the appearance of CTX-M-15 in the UK are extant. The aim of this study was to assess the presence of plasmid-encoded quinolone resistance genes in E. coli outside CTX-M-15-producing strains both historically and currently.
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Clinical isolates
Three different sets of bacterial isolates were examined:
- All national BSAC bacteraemia surveillance isolates of E. coli that were not ESBL producers but were quinolone-resistant (n = 110) from the earliest period of this structured surveillance in 2001 through to 2005.
- Regional Public Health Laboratory Service Midlands consecutive urinary isolates of E. coli (n = 521) collected for the assessment of chromogenic agars and identified by API 20E, BBL Crystal and molecular reference tests from the now disbanded Shrewsbury and Telford, Birmingham, Coventry and Stoke-on-Trent Public Health Laboratories in the period January to February 2000.15
- Local consecutive quinolone-resistant, non-ESBL E. coli (n = 105) isolates collected from routine community and hospital urine samples from Shrewsbury and Telford Hospital NHS Trust recovered on BBL Urinary Chromagar in the period August to September 2006. A random selection of 14 ESBL-producing E. coli was also collected during the same period.
Cystine lactose electrolyte depleted (CLED) agar was used to recover organisms for testing and Iso-Sensitest agar for susceptibility tests. Media were obtained from Oxoid Ltd, Basingstoke, UK.
Antibiotic susceptibility testing
Antibiotic disc diffusion tests were performed and interpreted according to the BSAC guidelines.16 ESBL production was detected by screening with 30 µg cefpodoxime discs (Oxoid Ltd) and then further testing with cefpodoxime and cefpodoxime/clavulanate discs to detect clavulanate enhancement 4 mm.16,17 Strains resistant to cefpodoxime/clavulanate were tested with cefpirome and cefpirome/clavulanate discs to exclude AmpC-producing strains masking ESBLs. Amikacin MICs were determined using Etests (AB Biodisk, Sweden).
PCR for the detection of the aac(6')-Ib gene
The aac(6')-Ib-cr gene was detected using methods based on those of Karisik et al.18 Two colonies of the test strain grown overnight on CLED plates at 37°C were re-suspended in 100 µL of molecular grade water. These were vortexed for 30 s and then centrifuged at 10 000 rpm for 10–15 s. The resulting supernatant was used as the DNA template. A negative control (molecular grade water) and two positive controls were included in each PCR run. Positive controls, one containing the native aac(6')-Ib gene and the second harbouring the aac(6')-Ib-cr gene, were obtained from Dr Neil Woodford (Antibiotic Resistance Monitoring and Reference Laboratory, Health Protection Agency).
PuReTaqTM Ready-To-GoTM PCR beads (GE Healthcare UK Ltd, UK) were used to amplify all aac(6')-Ib sequences. These beads are pre-mixed, pre-dispensed reactions for PCR (0.5 mL tubes containing reagents for a 25 µL PCR reaction). Each bead yields a reaction containing 
2.5 U of PuReTaq DNA polymerase, 200 µM of each dNTP in 10 mM Tris–HCl, 50 mM KCl, 1.5 mM MgCl2, stabilizers and BSA.
The following primer sequences (MWG Biotech AG, Ebersberg, Germany) were used: aac(6')-Ib fwd, 5'-ATG ACT GAG CAT GAC CTT GC-3'; and aac(6')-Ib rev, 5'-TTA GGC ATC ACT GCG TGT TC-3' at 50 ng/mL. A working primer mixture (1 µL of the 50 ng/µL solution and 22 µL of molecular grade water) was required for each reaction. DNA template (2 µL) was carefully dispensed onto the side of the Ready-To-Go tube, followed by 23 µL of the working primer solution to ‘wash down’ the DNA. Cycling conditions were: initial denaturation of the template DNA at 94°C for 5 min; 30 cycles of 94°C for 30 s, 60°C for 30 s and 72°C for 90 s; and a final elongation at 72°C for 7 min. PCR products were electrophoresed on a 1.5% (weight/volume) agarose gel containing 0.5 µg/mL ethidium bromide in Tris-borate EDTA (TBE) buffer and were observed under UV light.
Restriction fragment length polymorphism (RFLP)
RFLP was used to differentiate the native aac(6')-Ib gene from those of the cr variant of this gene.
To purify the amplified PCR DNA for RFLP, the IllustraTM GFX PCR and gel band purification kit (GE Healthcare UK Ltd) was used so that the resulting product was in water. For each of the PCR-positive samples, the cleaned amplicons were digested with NdeI and FokI restriction enzymes (Cambio Ltd, Cambridge, UK). A 5 µL aliquot from each product was digested separately for 4 h at 37°C with FokI and NdeI in a 10 µL reaction volume (mixture of 5 µL of DNA, 1 µL of enzyme buffer, 3 µL of molecular grade water and 1 µL of restriction enzyme). The amplicons encoding the native aminoglycoside acetyltransferase enzyme [aac(6')-Ib] were digested only by FokI, resulting in two predicted fragments of 224 and 295 bp. Amplicons encoding the fluoroquinolone-modifying variant of this enzyme [aac(6')-Ib-cr] were digested by only NdeI, producing two fragments of 453 and 66 bp. Two positive controls for aac(6')-Ib and aac(6')-Ib-cr were run in parallel with each RFLP digestion. Figure 1 shows a typical RFLP gel.
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Multiplex PCR for the detection of qnr genes
A multiplex PCR was used to simultaneously detect qnrA, qnrB and qnrS genes.19 The amplified DNA products were examined as described previously; the expected product sizes for qnrA, qnrB and qnrS were 580, 264 and 428 bp, respectively.
Serotyping of isolates was performed by Mr Tom Cheasty, Division of Enteric Pathogens, HPA Centre for Infection, Colindale, London, UK. MLST was carried out using the Achtman scheme.
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National bacteraemia isolates
Of the 110 ciprofloxacin-resistant, non-ESBL-producing isolates received, one was determined not to be E. coli and one was not viable. Isolates producing aac(6')-Ib-cr and their antibiotic susceptibilities are shown in Table 1. The four isolates identified as carrying this gene in 2001–02 were serotype O102 MLST type ST405 and in addition to ciprofloxacin were also resistant to co-amoxiclav, cefalexin, cefuroxime and trimethoprim, but susceptible to ceftazidime, gentamicin, nitrofurantoin and carbapenems. In 2004–05, five of the six isolates carrying this gene were serotype O25 MLST type ST131 and the remaining isolate was serotype O1 MLST type ST648. All these isolates were co-amoxiclav-resistant, three were cefalexin- and cefuroxime-resistant and one each was cefpodoxime-, gentamicin- or nitrofurantoin-resistant. None of the 108 bacteraemia isolates tested by multiplex PCR contained qnrA, B or S.
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Urinary isolates from 2000
Of the West Midlands isolates collected in 2000, 257 (49%) were amoxicillin-resistant, 28 (5%) were cefalexin-resistant, 10 (2%) were nitrofurantoin-resistant, 107 (21%) were trimethoprim-resistant and 10 (2%) were cefpodoxime-resistant (non-ESBL producers), but only 14 (3%) were resistant to norfloxacin. None of the 14 quinolone-resistant isolates carried the aac(6')-Ib-cr or the qnr gene. None of these isolates was typed.
One hundred and five consecutive quinolone-resistant, non-ESBL-producing local urinary isolates from 2006 were tested. Three patient isolates carried aac(6')-Ib-cr (serotypes O25, O1 and O non-typeable) and were epidemiologically unrelated. One of these patients with the O non-typeable strain had a urinary isolate 37 days later that was an amoxicillin-, co-amoxiclav- and ciprofloxacin-resistant, trimethoprim-susceptible, ESBL-producing E. coli. Neither of the other two patients had ESBL producers identified before or after the episode resulting in the positive isolate. One of the 105 isolates carried the native version of the aac(6')-Ib gene and another was found to harbour the qnrS gene, but neither carried aac(6')-Ib-cr.
Fourteen urinary isolates of ESBL-producing E. coli were saved from the same time period the non-ESBL-producing isolates were collected. Three of these isolates were ciprofloxacin-susceptible and were negative by PCR for aac(6')-Ib-cr. The remaining 11 ESBL-producing isolates were ciprofloxacin-resistant; 9 were positive for aac(6')-Ib-cr and 2 were negative.
Aminoglycoside susceptibilities
Of the aac(6')-Ib-cr-positive isolates, 9/10 bacteraemia isolates, 3/3 non-ESBL-producing urinary isolates from 2006 and 9/14 ESBL-producing urinary isolates from 2006 were gentamicin-susceptible but tobramycin-resistant. A further one bacteraemia isolate and four ESBL-producing urinary isolates were gentamicin- and tobramycin-resistant, and a single ESBL-producing urinary isolate from 2006 was tobramycin- and gentamicin-susceptible. The sole non-ESBL-producing urinary isolate with aac(6')-Ib was also gentamicin-susceptible and tobramycin-resistant. None of the other 95 bacteraemia strains and 101 non-ESBL-producing urinary isolates showed tobramycin resistance in the presence of gentamicin susceptibility. Not all of the gentamicin-resistant strains had positive PCRs for aac(6')-Ib-cr, as would be expected given the presence and spectrum of additional gentamicin resistance genes.
None of the isolates tested was amikacin-resistant. One bacteraemia isolate without the aac(6')-Ib or aac(6')-Ib-cr gene showed intermediate resistance to amikacin, as did one non-ESBL-producing 2006 urinary isolate carrying aac(6')-Ib-cr. All bacteraemia and urinary isolates whether ESBL-producing or not that had aac(6')-Ib-cr had an amikacin MIC 3 mg/L, whereas five randomly selected non-ESBL-producing 2006 urinary isolates and all ESBL isolates negative for aac(6')-Ib-cr had an amikacin MIC 
2 mg/L. This is summarized in Table 2.
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Discussion |
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The first report of the aac(6')-Ib-cr gene being present in European clinical isolates came when two different plasmids from clonal strains A and D of CTX-M-15 β-lactamase-producing E. coli isolated at our centre were characterized.20 Both reduced susceptibility to ciprofloxacin 4-fold when transferred into another E. coli. The gene has also been detected in isolates of CTX-M-15 ESBL-producing E. coli and K. pneumoniae in Portugal21 and Canada13 as well as CTX-M plasmids from K. pneumoniae in Africa.22 In China, where CTX-M-14 and CTX-M-24 are the most prevalent, the aac(6')-Ib-cr gene was detected in 9.9% of the ESBL-producing E. coli and K. pneumoniae.9 In our study, 9 of the 11 ciprofloxacin-resistant, ESBL-producing urinary E. coli isolates tested carried the aac(6')-Ib-cr gene, whereas 0 of the 3 ciprofloxacin-susceptible ESBL producers carried the gene.
The original description of combinations of qnr and aac(6')-Ib-cr and of an E. coli strain harbouring qnrA treated with norfloxacin, where high-level resistance developed through chromosomal mutations affecting gyrase and topoisomerase enzymes,23 suggested that these genes might have accounted for the quinolone resistance rise in 1995–2001 prior to the European appearance of CTX-M strains. Our study does not suggest this, and qnr genes were uncommon in English unlike Chinese E. coli. Our findings are compatible either with the exogenous introduction of CTX-M-15 and aac(6')-Ib-cr to the UK or with local recombination of CTX-M genes with aac(6')-Ib-cr-containing strains.
Classical AAC(6')-I enzymes acetylate and usually confer resistance to tobramycin and amikacin, but not to gentamicin.24 However, in our isolates, the aac(6')-Ib-cr gene did not confer resistance to amikacin in terms of clinical breakpoints. Nevertheless, there was a clear distinction between those isolates harbouring the aac(6')-Ib-cr gene that had MICs of 3 mg/L or higher and those that did not (MICs of 2 mg/L or lower). Therefore, amikacin might remain useful in aac(6')-Ib-cr- and CTX-M-15-positive, multiresistant isolates, but this remains to be clinically verified despite the paucity of antibiotics other than carbapenems with a useful Gram-negative spectrum for ESBLs.
No plasmid-mediated quinolone resistance mechanisms were detected in the small number (n = 14) of quinolone-resistant E. coli urinary isolates collected in the West Midlands in 2000. Resistance was rarer (3.7%) than in the bacteraemia isolates described by Livermore et al.14 In contrast, in local urine samples from 2006, the aac(6')-Ib-cr gene was present in 3% of ciprofloxacin-resistant, non-ESBL-producing E. coli isolates. In Canada,13 aac(6')-Ib-cr-positive, non-ESBL-producing E. coli strains increased from 2.9% in 2003 to 6.1% in 2007 and were associated with an increase in CTX-M-15 strains. Our experience of an increase from 0% in 2001 to 3% in 2006 is similar.
One of the 105 local urine isolates tested carried a qnr gene, qnrS. No qnr genes were detected in the 110 bacteraemia strains of quinolone-resistant E. coli sent from 27 UK centres between 2001 and 2005, but 9% of the isolates tested harboured the aac(6')-Ib-cr gene. These strains did not increase in frequency in E. coli bacteraemia over the 5 years. The aac(6')-Ib-cr gene was found in non-ESBL-producing E. coli isolates sent from six geographically dispersed centres. Four centres sent two isolates each.
Isolates from 2001 and 2002 were type O102-ST405. Interestingly, serotype O102 H6 was one of the earliest (1997–2001) recovered strains from Israeli CTX-M-2 outbreaks.25 From 2004 onwards, the E. coli non-ESBL-producing isolates from the national bacteraemia surveillance and current local urinary isolates that carried the aac(6')-Ib-cr gene were serotypes O25, O1 and O non-typeable. The bacteraemia O25 isolates were ST131 and the O1 isolate ST648. These strains could have gained the quinolone resistance gene aac(6')-Ib-cr, but not the gene encoding CTX-M-15 as possibly exemplified by one of our patients or might be ST131 isolates without CTX-M-15. Some local urinary and the five 2004–05 national bacteraemia isolates were of serotype O25. Recent emergence in Europe of ciprofloxacin-resistant E. coli O25-ST131 without CTX-M-15 (138/148 strains) has been reported26 simultaneously (2003–06) with the emergence of intercontinental CTX-M-15 O25-ST131 E. coli,11 but this report did not include British strains or analysis for aac(6')-Ib-cr. It is interesting that the 2004–05 bacteraemia isolates were co-amoxiclav-resistant. In the sequence of the pEK499 plasmid in Group A serotype O25 described from the UK CTX-M-15 ST131 clonal outbreak, the gene encoding OXA-1 (conferring β-lactamase-inhibitor resistance) was the closest gene linked to aac(6')-Ib-cr flanked by IS26 and transposon A sequences.27 The occurrence of the gene encoding OXA-1 and aac(6')-Ib-cr in an integron has been described previously in CTX-M-15 strains.6,7,22 It is not clear whether the European clonal group has similar co-amoxiclav resistance. The serotype as well as aac(6')-Ib-cr may be capable of transferring to other strains. O25 antigens in E. coli are not necessarily allelic with other O antigens and, like O1 antigens, can be transferred between strains with the his locus.28 The different sequence type of serotype O102 antecedent UK bacteraemia strains lacking by antibiotic resistance phenotype only the CTX-M gene, makes such a relationship with the subsequent O25 serotype strain unlikely.
Our study shows that aac(6')-Ib-cr occurred in E. coli in the UK prior to the introduction of CTX-M-15, albeit at a relatively low level and apparently in a single type as judged by bacteraemia isolates. This type O102 ST405 with aac(6')-Ib-cr has now been replaced by O25 and O1 strains. Whether strains of type O102 ST405 contributed to plasmids of the current CTX-M-15 strains, including ST131, requires further study of their lineage by analysis of plasmids, extraintestinal virulence factors and clades.
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The consumable cost of this work was supported by funds from R. E. W.'s University of Birmingham Research Fund. G. Ll. J.'s training programme and salary was funded by the Workforce Development Directorate, Birmingham & Black Country SHA. T. G. is supported by a studentship from the Government of the Great Socialist People's Libyan Arab Jamahiriya.
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None to declare.
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Acknowledgements |
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This work was presented in part at the Eighteenth European Congress of Clinical Microbiology and Infectious Disease, Barcelona, 2008, supported by a travel grant from ECCMID to G. Ll. J.
We acknowledge Mr Tom Cheasty for performing the serotyping, the BSAC bacteraemia surveillance programme for providing test isolates, Dr Neil Woodford for technical assistance and providing positive control material and Drs George Jacoby and Katie Hopkins for the qnr controls.
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References |
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1 . Martinez-Martinez L, Pascual A, Jacoby GA. Quinolone resistance from a transferable plasmid. Lancet (1998) 351:797–9.[CrossRef][Web of Science][Medline]
2 . Tran JH, Jacoby GA. Mechanism of plasmid-mediated quinolone resistance. Proc Natl Acad Sci USA (2002) 9:5638–42.
3
.
Jacoby GA, Walsh KE, Mills DM, et al. qnrB, another plasmid-mediated gene for quinolone resistance. Antimicrob Agents Chemother (2006) 50:1178–82.
4
.
Hata M, Suzuki M, Matsumoto M, et al. Cloning of a novel gene for quinolone resistance from a transferable plasmid in Shigella flexneri 2b. Antimicrob Agents Chemother (2005) 49:801–3.
5
.
Wang M, Tran JH, Jacoby GA, et al. Plasmid-mediated quinolone resistance in clinical isolates of Escherichia coli from Shanghai, China. Antimicrob Agents Chemother (2003) 47:2242–8.
6 . Robicsek A, Strahilevitz J, Jacoby GA, et al. Fluoroquinolone-modifying enzyme: a new adaptation of a common aminoglycoside acetyltransferase. Nat Med (2006) 12:83–8.[CrossRef][Web of Science][Medline]
7
.
Boyd DA, Tyler S, Christianson S, et al. Complete nucleotide sequence of a 92-kilobase plasmid harbouring the CTX-M-15 extended-spectrum β-lactamase involved in an outbreak in long-term-care facilities in Toronto, Canada. Antimicrob Agents Chemother (2004) 48:3758–64.
8
.
Park CH, Robicsek A, Jacoby GA, et al. Prevalence in the United States of aac(6')-Ib-cr encoding a ciprofloxacin-modifying enzyme. Antimicrob Agents Chemother (2006) 50:3953–5.
9
.
Jiang Y, Zhou Z, Qian Y, et al. Plasmid-mediated quinolone resistance determinants qnr and aac(6')-Ib-cr in extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae in China. J Antimicrob Chemother (2008) 61:1003–6.
10 . Canton R, Coque TM. The CTX-M β-lactamase pandemic. Curr Opin Microbiol (2006) 9:466–75.[CrossRef][Web of Science][Medline]
11
.
Nicolas-Chanoine MH, Blanco J, Leflon-Guibout V, et al. Intercontinental emergence of Escherichia coli clone O25:H4-ST131 producing CTX-M-15. J Antimicrob Chemother (2008) 61:273–81.
12 . Warren RE, Harvey G, Carr R, et al. Control of infections due to extended-spectrum β-lactamase-producing organisms in hospitals and the community. Clin Microbiol Infect (2008) 14(Suppl 1):124–33.[Medline]
13
.
Pitout JD, Wei Y, Church DL, et al. Surveillance for plasmid-mediated quinolone resistance determinants in Enterobacteriaceae within the Calgary Health Region, Canada: the emergence of aac(6')-Ib-cr. J Antimicrob Chemother (2008) 61:999–1002.
14
.
Livermore DM, Nichols T, Lamagni TL, et al. Ciprofloxacin-resistant Escherichia coli in England: increasingly prevalent and mostly from men. J Antimicrob Chemother (2003) 52:1040–2.
15
.
Fallon D, Andrews N, Frodsham D, et al. A comparison of the performance of commercially available chromogenic agars for the isolation and presumptive identification of organisms from urine. J Clin Pathol (2002) 55:524–9.
16
.
Andrews JM. BSAC standardized disc susceptibility testing method (version 5). J Antimicrob Chemother (2006) 58:511–29.
17 . Livermore DM, Brown DFJ. Detection of β-lactamase-mediated resistance. J Antimicrob Chemother (2001) 48(Suppl 1):59–64.[Abstract]
18 . Karisik E, Ellington MJ, Pike R, et al. Wide occurrence of the fluoroquinolone-modifying acetyltransferase gene aac(6')-Ib-cr in CTX-M-positive Escherichia coli from the United Kingdom. In: Abstracts of the Forty-sixth Interscience Conference on Antimicrobial Agents and Chemotherapy, San Francisco, CA, USA, 2006. Washington, DC, USA: American Society for Microbiology. Abstract C2-110, p.104.
19
.
Cattoir V, Poirel L, Rotimi V, et al. Multiplex PCR for detection of plasmid-mediated quinolone resistance qnr genes in ESBL-producing enterobacterial isolates. J Antimicrob Chemother (2007) 60:394–7.
20 . Karisik E, Underwood A, Ellington MJ, et al. Complete nucleotide sequence of pEK499, a multidrug-resistance plasmid from the UK's most prevalent Escherichia coli strain with CTX-M-15 β-lactamase. In: Abstracts of the Seventeenth European Congress of Clinical Microbiology and Infectious Diseases, Munich, Germany, 2007. Abstract P864.
21
.
Machado E, Coque TM, Sousa JC, et al. Dissemination in Portugal of CTX-M-15-, OXA-1-, and TEM-1-producing Enterobacteriaceae strains containing the aac(6')-Ib-cr gene, which encodes an aminoglycoside- and fluoroquinolone-modifying enzyme. Antimicrob Agents Chemother (2006) 50:3220–1.
22
.
Soge OO, Adeniyi BA, Roberts MC. New antibiotic resistance genes associated with CTX-M plasmids from uropathogenic Nigerian Klebsiella pneumoniae. J Antimicrob Chemother (2006) 58:1048–53.
23
.
Poirel L, Pitout JDD, Calvo L, et al. In vivo selection of fluoroquinolone-resistant Escherichia coli isolates expressing plasmid-mediated quinolone resistance and expanded-spectrum β-lactamase. Antimicrob Agents Chemother (2006) 50:1525–7.
24
.
Rather PN, Munayyer H, Mann PA, et al. Genetic analysis of bacterial acetyltransferases: identification of amino acids determining the specificities of the aminoglycoside 6'-N-acetyltransferase Ib and IIa proteins. J Bacteriol (1992) 174:3196–203.
25
.
Sompolinsky D, Nitzan Y, Tetry S, et al. Integron-mediated ESBL resistance in rare serotypes of Escherichia coli causing infections in an elderly population of Israel. J Antimicrob Chemother (2005) 55:119–22.
26
.
Cagnacci S, Gualco L, Debbia E, et al. European emergence of ciprofloxacin-resistant Escherichia coli clonal groups O25:H4-ST131 and O15:K52:H1 causing community-acquired uncomplicated cystitis. J Clin Microbiol (2008) 46:2605–12.
27
.
Karisik E, Ellington MJ, Pike R, et al. Molecular characterization of plasmids encoding CTX-M-15 β-lactamases from Escherichia coli strains in the United Kingdom. J Antimicrob Chemother (2006) 58:665–8.
28
.
Orskov I, Orskov F, Jann B, et al. Serology, chemistry, and genetics of O and K antigens of Escherichia coli. Bacteriol Rev (1977) 41:667–710.
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