JAC Advance Access published online on November 11, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn470
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Original research |
Characterization of plasmids harbouring qnrS1, qnrB2 and qnrB19 genes in Salmonella
1 Department of Infectious, Parasitic and Immune-Mediated Diseases, Istituto Superiore di Sanità, Rome, Italy 2 Central Veterinary Institute (CVI) of Wageningen UR, PO Box 2004, 8203 AA Lelystad, The Netherlands 3 Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
* Correspondence address. Department of Infectious, Parasitic and Immune-Mediated Diseases, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy. Tel: +39-06-4990-3128; Fax: +39-06-4938-7112; E-mail: alecara{at}iss.it
Received 30 July 2008; returned 28 August 2008; revised 13 October 2008; accepted 14 October 2008
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and methodsResultsDiscussionFundingTransparency declarationsSupplementary dataReferences |
|---|
Objectives: The aim of this study was to identify and characterize plasmids carrying qnrS1, qnrB2 and qnrB19 genes identified in Salmonella strains from The Netherlands. The identification of plasmids may help to follow the dissemination of these resistance genes in different countries and environments.
Methods: Plasmids from 33 qnr-positive Salmonella strains were transferred to Escherichia coli and analysed by restriction, Southern blot hybridization, PCR and sequencing of resistance determinants. They were also assigned to incompatibility groups by PCR-based replicon typing, including three additional PCR assays for the IncU, IncR and ColE groups. The collection included isolates from humans and one from chicken meat.
Results: Five IncN plasmids carrying qnrS1, qnrB2 and qnrB19 genes were identified in Salmonella enterica Bredeney, Typhimurium PT507, Kentucky and Saintpaul. qnrS1 genes were also located on three further plasmid types, belonging to the ColE (in Salmonella Corvallis and Anatum), IncR (in Salmonella Montevideo) and IncHI2 (in Salmonella Stanley) groups.
Conclusions: Multiple events of mobilization, transposition and replicon fusion generate the complexity observed in qnr-positive isolates that are emerging worldwide. Despite the fact that the occurrence of qnr genes in bacteria from animals is scarcely reported, these genes are associated with genetic elements and located on plasmids that are recurrent in animal isolates.
Key Words: QNR , LAP-2 , quinolone resistance , replicon-typing , animal reservoir
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionFundingTransparency declarationsSupplementary dataReferences |
|---|
Plasmid-mediated quinolone resistance is emerging worldwide in Enterobacteriaceae, including Salmonella enterica.1,2 Salmonellosis is treated with fluoroquinolones only in elderly or immunocompromised patients, but these drugs are also used for treating patients with enteric fever, invasive disease or long-term salmonellae carriage. Recent studies on Salmonella showed that plasmid-located qnr genes confer decreased susceptibility to fluoroquinolones (MIC >0.06 mg/L) and nalidixic acid (MIC 8–16 mg/L), without association with mutations in the topoisomerase genes.3–9 Recently, we reported the first qnrB and qnrS genes in Salmonella isolates from patients and a broiler chicken in The Netherlands.5 These genes were previously described in Salmonella from the USA, Asia, Africa and Europe, but scarce information is available on the structure and circulation of plasmids carrying the different qnr gene variants.3–9 Currently, there are two completely sequenced plasmids carrying the qnrS1 gene: one is named pTPqnrS-1a, a 10 kb plasmid obtained from a multiresistant S. enterica Typhimurium DT193 in the UK;3 the other is pK245, a 98 kb multireplicon plasmid identified in a clinical Klebsiella pneumoniae from Taiwan.10 DNA sequences of these plasmids highlighted some peculiar features that can be helpful to trace them and also provide information on the mechanisms responsible for the horizontal transfer of the qnr genes among different isolates. Plasmid pTPqnrS-1a exhibited 89% nucleotide sequence identity to the ColE-plasmid pEC278 isolated from a pathogenic Escherichia coli strain (GenBank accession number AY589571 [GenBank] ) and the region adjacent to the origin of replication (oriV) showed 99% identity to plasmid pINF5 from Salmonella Infantis isolated from chicken carcasses in Germany.6 The pK245 plasmid structure was also complex, being composed of four main scaffolds: (i) a region deriving from an IncF plasmid; (ii) a region deriving from the IncQ plasmid RSF1010; (iii) a region encoding the RepA replication initiator protein found in Pantoea stewartii plasmid pSW800 (70% similarity); and (iv) a region encoding the blaLAP-2 and qnrS genes, and the repB gene of the K. pneumoniae pGSH500 plasmid (96% similarity).10
Plasmids of the IncU (p37) and IncQ (pGNB2) groups were associated with the qnrS2 gene: in Aeromonas punctata from France and in plasmid DNA obtained from a wastewater treatment plant in Germany, respectively.11,12 Finally, the qnrA1 gene associated with the blaVEB-1 gene emerged worldwide located on IncA/C2 plasmids,13 while little information is available on plasmids carrying the qnrB variants.
The aim of this study was to identify and characterize plasmids harbouring qnrS1, qnrB2 and qnrB19 genes identified in quinolone-resistant Salmonella strains from The Netherlands, with the final objective to provide a set of specific PCR assays, useful for monitoring the dissemination of these resistance traits in different countries and environments.
|
Materials and methods |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionFundingTransparency declarationsSupplementary dataReferences |
|---|
Strains
A total of 33 qnr-positive Salmonella strains were analysed in this study. Most of the isolates were from patients from The Netherlands, and one strain (137.25) was from chicken meat (Table 1). The presence of qnr genes in these strains was previously described.5 qnrS1-positive salmonellae belong to serotypes Corvallis (25 isolates), Kentucky (n = 2), Anatum (n = 1), Montevideo (n = 1), Stanley (n = 1) and Saintpaul (n = 1) (Table 1). Comparison of pulsed-field gel electrophoresis (PFGE) patterns of Corvallis strains suggested that they were clonally related (>90% of similarity), with the exception of two recent isolates of 2006 (strains 162.58 and 163.43), showing unrelated PFGE profiles (<80% similarity). One Salmonella Bredeney and one Typhimurium PT507 were positive for qnrB2 and qnrB19 (formerly referred to as qnrB5')5 genes, respectively. The qnrB5' gene name was updated by DNA sequencing of the amplicon generated by the primers QnrB10/19Fw and QnrB10/19Rv listed in Table 2 identified as qnrB1914 by comparison with the GenBank database and Lahey Clinic web site. The DNA sequence of the quinolone resistance determining region (QRDR) of the gyrA and parC genes was analysed for all the strains.15
|
|
Antimicrobial susceptibility
The resistance patterns were determined by broth microdilution according to EUCAST guidelines (www.eucast.org) using microtiter trays (TREK Diagnostic Systems, UK).
MIC breakpoints used for susceptibility and resistance to ciprofloxacin were 
0.5 and >1 mg/L, respectively, and for resistance to nalidixic acid it was >16 mg/L as recommended by EUCAST.
Plasmid-mediated quinolone resistance transferability
Plasmid DNA was purified by the Qiagen Plasmid Midikit (Qiagen Inc., Milan, Italy). Purified plasmids were used to transform MAX Efficiency DH5
E. coli chemically competent cells (Invitrogen, Milan, Italy). DH5 was chosen as the recipient because it is capable of being transformed efficiently with large plasmids.16 However, this strain is resistant to nalidixic acid (MIC >64 mg/L) due to mutations in the gyrA gene, but it is fully susceptible to ciprofloxacin with an MIC of 0.03 mg/L (Table 1). Consequently, transformants (T) were selected on LB agar plates containing 0.06 mg/L ciprofloxacin.
Conjugation experiments were performed at 25°C by liquid mating assay using a rifampicin-resistant E. coli CSH26 as recipient and selecting transconjugants (Tc) on LB agar supplemented with 100 mg/L rifampicin and 0.06 mg/L ciprofloxacin.17
Undigested [Figure S1; see Supplementary data at JAC Online (http://jac.oxfordjournals.org./] and PvuII restricted plasmids in the original and recipient strains were analysed by Southern blot hybridization using the digoxigenin-labelled qnrS, qnrB and repN amplicons as probes (PCR DIG probe synthesis kit, Roche Diagnostics GmbH, Mannheim, Germany).18,19 Hybridization and detection were performed according to the manufacturer’s instructions.
Plasmids from parental and transformant/transconjugant strains were assigned to incompatibility groups by PCR-based replicon typing (PBRT) performed on total DNA using previously described primers and conditions.19 Total DNA was obtained by the Wizard Genomic DNA Purification System (Promega, Madison, WI, USA). Plasmids that were negative for the 18 replicons of the PBRT scheme were tested for three additional targets: the oriV of ColE-like plasmids (colE PCR), the repA gene of the pRA3 plasmid from Aeromonas hydrophila (IncU PCR) and the repB gene of the K. pneumoniae qnrS1-plasmid pK245. Since plasmid pK245 was not assigned to any known Inc group, this assay was named IncR PCR (Table 2). Amplicons were sequenced for confirmation. The colE PCR was devised to amplify all the colE-like plasmids. A colETp amplification was devised to specifically detect the subset of ColE-positive plasmids showing a different oriV sequence (74% of homology with the other ColE-like variants), but 100% identical to that of the pTPqnrS-1a plasmid from Salmonella Typhimurium DT193 (GenBank accession number AM746977 [GenBank] ). Primers are listed in Table 2.
ColETp-positive strains were further analysed by the qnrS-colETp PCR (Table 2) to confirm the co-linearity of the qnrS1 gene with the colETp oriV, as described in the pTPqnrS-1a plasmid. Furthermore, the qnrS1 and colETp oriV containing region of plasmid 138.31(T) was cloned and fully sequenced by ligating the PstI digested plasmid into the pZero-2.1 kanamycin-resistant vector (Invitrogen). Ligation mixture was introduced by transformation into the MAX Efficiency E. coli DH5 chemically competent cells (Invitrogen). Transformants were selected on LB agar plates, containing 100 mg/L kanamycin and 0.06 mg/L ciprofloxacin. Recombinant plasmids were extracted by the Qiagen Plasmid Midikit (Qiagen Inc.) and inserts were sequenced on both strands by standard and walking primers.
Plasmids assigned by PBRT to the IncHI2 group were further typed applying the previously described HI2-plasmid typing scheme, consisting of 10 PCRs, devised on the IncHI2 R478 and pAPEC-O1-R plasmids (Table 2).20
All plasmids were also screened for the presence of the blaLAP, blaOXA, blaTEM, aac(6’)-Ib-cr and qepA genes and for the presence of IS2 flanking the qnrS1 gene (Table 2).21–24
|
Results |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionFundingTransparency declarationsSupplementary dataReferences |
|---|
Localization of qnr and β-lactamase genes on Salmonella plasmids
Qnr-positive plasmids were successfully transferred by transformation from all the parental strains to the recipient E. coli DH5 strain (the 131.17 strain was chosen as representative for the Salmonella Corvallis clonal strain), with the exception of the Salmonella Stanley strain 146.71 that did not produce transformants; however, it positively transferred the plasmid by conjugation (Table 1). PCR and DNA sequencing experiments confirmed the qnr-gene presence in all transformants/transconjugants obtained (Table 1). MICs of ciprofloxacin and nalidixic acid were determined for the parental and recipient strains and for the empty CSH26 and DH5 E. coli recipient strains (Table 1). Parental and recipient strains were PCR negative for the presence of the aac(6’)-Ib-cr and qepA genes, conferring reduced susceptibility to fluoroquinolones. No mutations previously described to be associated with quinolone resistance were identified in the QRDR of the parental strains (data not shown).
Ampicillin resistance was associated with the presence of the blaTEM gene in all strains, except strain 146.71(Tc), which was positive for the blaLAP gene, identified by DNA sequencing of the amplicon as the blaLAP-2 gene variant.25
Typing of both qnrB2 and qnrB19 plasmids
Plasmids from both parental and recipient strains were tested for 21 replicons (listed in Table 2 and reference 19).
Both qnrB2 and qnrB19 genes were located on IncN plasmids (100% identity to the repA gene of the R46 IncN reference plasmid, GenBank accession number AY046276 [GenBank] ). ColE plasmids were also identified in the parental strains but they were qnr-negative and were not transferred to the recipient strain (Table 1).
IncN plasmids in the transformant strains were further analysed by PvuII RFLP and the localization of the qnr gene was confirmed by Southern blot hybridization experiments (Figure 1).
|
Typing of qnrS1 plasmids
The qnrS1 genes were located on four different plasmid types.
(i) ColE-like plasmids of 
10 kb were identified in all Salmonella Corvallis and Salmonella Anatum strains. Several strains also showed co-resident I1, B/O or A/C type plasmids, which were not transferred by transformation. DNA sequencing of the ColE-amplicons obtained from strains 138.31, 131.17 and 120.52 revealed that these plasmids had the origin of replication identical to that of the pTPqnrS-1a plasmid of Salmonella Typhimurium DT193.3 The presence of this type of oriV was then confirmed in all the Salmonella Anatum and Salmonella Corvallis strains by PCR assay specific for the ColETp oriV (Table 1). Furthermore, all these strains were also positive for the qnrS-colETp PCR indicating the localization of the qnrS1 gene on pTPqnrS-1a-like plasmids. This observation was confirmed by cloning and fully sequencing the 4375 bp PstI fragment from plasmid 138.31(T). This region contained the mobC gene, the oriV and the qnrS1 gene in an array identical to that previously described for the pTPqnrS-1a plasmid.
(ii) The qnrS1 gene was identified on IncN plasmids of 50 kb in the Salmonella Kentucky and Saintpaul strains. Replicons of the I1- and P-type were also detected in the Salmonella Kentucky parental strain but they were not transferred to the recipient strain. A co-resident ColE plasmid was identified in the Saintpaul strain but it was qnr-negative and not transferred by transformation. IncN plasmids from the transformants were further analysed by PvuII RFLP and the localization of the qnr gene was confirmed by Southern blot hybridization (Figure 1).
(iii) The qnrS1 gene was also identified on an IncHI2 plasmid in Salmonella Stanley strain 146.71 and its relative transconjugants (Table 1). Plasmid DNA from this strain could not be purified (the estimated minimal size for IncHI2 plasmids is >250 kb), but the transferred plasmid was further characterized applying the previously described HI2-typing scheme, discerning the two reference IncHI2 R478 and pAPEC-O1-R plasmids (Table 2).20 This analysis identified the IncHI2 plasmid from Salmonella Stanley as a pAPEC-O1-R-like plasmid. In fact, it lacked three genes that are present in the R478 but are missing in pAPEC-O1-R (smr92, smr93 and smr201) and it was positive for the O1R_160 locus, which is disrupted by the Tn10 insertion in R478.26 The qnrS1-HI2pAPEC-O1-R plasmid conferred resistance to ampicillin, aminoglycosides, sulphonamides, streptomycin, tetracycline and chloramphenicol and it was positive for the blaLAP-2 gene.
(iv) The qnrS1 gene was located on an IncR plasmid of 50 kb in the Salmonella Montevideo strain. This plasmid conferred a multidrug-resistant phenotype, including aminoglycosides, chloramphenicol and tetracycline resistance. The parental strain was also positive for a qnr-negative ColE plasmid.
All the qnrS1 genes, regardless of their locations on the different plasmid scaffolds, were flanked by truncated IS2 elements as previously described.3,27
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionFundingTransparency declarationsSupplementary dataReferences |
|---|
This study describes plasmids harbouring qnr genes identified in eight different Salmonella serovars from The Netherlands. The sample included isolates from humans and one from chicken meat. IncN plasmids were the most recurrent plasmid type since the three qnr gene variants, qnrS1, qnrB2 and qnrB19, were located on this kind of plasmid in four different Salmonella serotypes, from both human and the animal sources. Four of the five IncN plasmids showed a common scaffold and variable PvuII fragments corresponding to the variable region containing the qnr gene. It is interesting to note that qnrS1-positive IncN plasmids were also identified in Salmonella Virchow isolated in the UK in 2004–2005, causing an outbreak associated with imported cooked meat from Thailand7 and the qnrS plasmid pINF5 from Salmonella Infantis was hypothesized to have an IncN plasmid-like ancestor (pMUR050).6 The association qnr–IncN is likely a fortuitous event of integration of the Qnr determinant into a very common plasmid species. IncN was the most frequently identified (26%) plasmid type in a collection of 58 multidrug-resistant S. enterica strains from animals and food of animal origin isolated in Italy in 2000–2001.19,28 Furthermore, in a study performed on a large collection of E. coli isolates from the USA, the prevalence of IncN plasmids was 10.9% and 16.1% in avian faecal and pathogenic E. coli, respectively, but interestingly, E. coli strains from the faeces of healthy humans and from human urinary tract infections were all negative for IncN plasmids.29 Therefore, it is plausible that IncN plasmids are common in zoonotic enterobacterial pathogens, but rarer in bacteria from humans, suggesting that IncN Salmonella plasmids could have acquired the qnr gene by transposition events occurring in animals.
The qnrS1 gene was also located on small ColE-like plasmids in Salmonella Corvallis and Anatum strains. The Corvallis serotype carrying the qnrS1 gene recently emerged in Denmark, associated with the consumption of imported food products from Thailand. Twenty-three isolates showing related PFGE patterns were obtained from humans from Denmark and Thailand and from chicken, pork and beef imported from Thailand.30 The Salmonella Corvallis PFGE patterns were also very similar to those described in that study (data not shown). It could be speculated that the ColETp-qnrS1 plasmid is present also in Salmonella Corvallis from Denmark and Thailand and contributed to the worldwide spread of qnrS1 gene in this clone. However, the association Salmonella Corvallis–ColETp–qnrS1 is not exclusive, since the same plasmid was identified in Salmonella Typhimurium and Virginia in the UK, and in Anatum in this study. Recently, a small qnrS1-positive plasmid showing 99% homology with the pTPqnrS-1a plasmid was also identified in a Salmonella Typhimurium isolated in Taiwan (GenBank accession number EU715253 [GenBank] ), suggesting that this plasmid is very common worldwide, but it seems to have a preference for the Salmonella species. More in general, ColE-like plasmids are largely present in Enterobacteriaceae and they are not self-conjugative, but they can be mobilized by co-resident conjugative plasmids, through the presence of the mobABC genes.31 The simultaneous presence of the ColETp-qnrS plasmid with additional plasmids belonging to the I1, B/O or A/C groups within the same parental strain strongly suggests that the latter plasmids can participate in the mobilization of the small ColE plasmids, promoting their circulation in different Salmonella serotypes.
In this study, the qnrS1 gene was, for the first time, located on an IncHI2 plasmid identified in a Salmonella Stanley strain. The plasmid scaffold resembled the pAPEC-O1-R plasmid previously described in avian pathogenic E. coli in the USA.26 It is important to note that HI2pAPEC-O1-R plasmid variants were recently recognized in Salmonella Virchow producing the extended-spectrum β-lactamase (ESBL) CTX-M-2 from poultry flocks, poultry meat and humans in Belgium and French Guyana.32 The chronology of isolation of those strains suggested that these bacteria were transmitted to humans via the food chain, specifically by poultry meat. The blaCTX-M-2 gene was not present on the original pAPEC-O1-R plasmid26 and it was not identified on the qnrS1-HI2pAPEC-O1-R plasmid either. In conclusion, the HI2 plasmid variant associated with avian pathogenic E. coli in the USA has evolved by acquisition of ESBL or qnr genes in Salmonella in Europe.
The fourth plasmid type carrying the qnrS1 gene was the IncR plasmid identified in the Salmonella Montevideo strain. The replicase gene of this plasmid was the same as that of the previously described pK245 plasmid from K. pneumoniae, showing the association qnrS1–blaLAP-2 genes. The IncR plasmid from Salmonella Montevideo was not positive for the blaLAP-2 gene, which was identified on the IncHI2 plasmid from the Salmonella Stanley.
From our findings, a complex figure of variably assorted plasmid replicons and resistance determinants clearly appears. Common genetic traits are organized on different scaffolds in the various strains. Multiple events of mobilization, transposition, illegitimate recombination, replicon fusion and resolution can generate the apparent complexity observed in the different qnr-positive isolates that are emerging worldwide, but these are in fact, mosaics of recurrent genetic traits. Despite the low prevalence of qnr genes in bacteria from animals in comparison with isolates from humans, these genes were located on plasmids frequently associated with E. coli and Salmonella isolates from animals and rarely occurring in humans. This aspect would merit a further investigation of the prevalence of qnr genes in the faecal flora from animals as a potential unexpected source for these resistance genes.
|
Funding |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionFundingTransparency declarationsSupplementary dataReferences |
|---|
This work has been partly funded by Med-Vet-Net, Workpackages 21 and 29. Med-Vet-Net is an EU-funded Network of Excellence.
|
Transparency declarations |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionFundingTransparency declarationsSupplementary dataReferences |
|---|
None to declare.
|
Supplementary data |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionFundingTransparency declarationsSupplementary dataReferences |
|---|
Figure S1 is available as Supplementary data at JAC Online (http://jac.oxfordjournals.org/).
|
Acknowledgements |
|---|
We are grateful to Professor Patrice Nordmann for kindly providing us with the positive control for the IncU plasmids and to Tonino Sofia for critical reading of the manuscript.
|
References |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionFundingTransparency declarationsSupplementary dataReferences |
|---|
1 . Robicsek A, Hooper DC. The worldwide emergence of plasmid-mediated quinolone resistance. Lancet Infect Dis (2006) 6:629–40.[CrossRef][Web of Science][Medline]
2 . 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]
3
.
Kehrenberg A, Hopkins KL, Threlfall EJ, et al. Complete nucleotide sequence of a small qnrS1-carrying plasmid from Salmonella enterica subsp. enterica Typhimurium DT193. J Antimicrob Chemother (2007) 60:903–5.
4 . Gay K, Robicsek A, Strahilevitz J, et al. Plasmid-mediated quinolone resistance in non-Typhi serotypes of Salmonella enterica. Clin Infect Dis (2006) 43:297–304.[CrossRef][Web of Science][Medline]
5
.
Veldman K, van Pelt W, Mevius D. First report of qnr in Salmonella in The Netherlands. J Antimicrob Chemother (2008) 61:452–3.
6
.
Kehrenberg C, Friederichs S, de Jong A, et al. Identification of the plasmid-borne quinolone resistance gene qnrS in Salmonella enterica serovar Infantis. J Antimicrob Chemother (2006) 58:18–22.
7
.
Hopkins KL, Wootton L, Day MR, et al. Plasmid-mediated quinolone resistance determinant qnrS1 found in Salmonella enterica strains isolated in the UK. J Antimicrob Chemother (2007) 59:1071–5.
8
.
Cattoir V, Weill FX, Poirel L, et al. Prevalence of qnr genes in Salmonella in France. J Antimicrob Chemother (2007) 59:751–4.
9
.
Iabadene H, Messai Y, Ammari H, et al. Dissemination of ESBL and Qnr determinants in Enterobacter cloacae in Algeria. J Antimicrob Chemother (2008) 62:133–6.
10
.
Chen YT, Shu HY, Li LH, et al. Complete nucleotide sequence of pK245, a 98-kilobase plasmid conferring quinolone resistance and extended-spectrum-beta-lactamase activity in a clinical Klebsiella pneumoniae isolate. Antimicrob Agents Chemother (2006) 50:3861–6.
11 . Cattoir V, Poirel L, Aubert C, et al. Unexpected occurrence of plasmid-mediated quinolone resistance determinants in environmental Aeromonas spp. Emerg Infect Dis (2008) 14:231–7.[Web of Science][Medline]
12
.
Bönemann G, Stiens M, Pühler A, et al. Mobilizable IncQ-related plasmid carrying a new quinolone resistance gene, qnrS2, isolated from the bacterial community of a wastewater treatment plant. Antimicrob Agents Chemother (2006) 50:3075–80.
13 . Poirel L, Villa L, Bertini A, et al. Expanded-spectrum beta-lactamase and plasmid-mediated quinolone resistance. Emerg Infect Dis (2007) 13:803–5.[Web of Science][Medline]
14
.
Cattoir V, Nordmann P, Silva-Sanchez J, et al. ISEcp1-mediated transposition of qnrB-like gene in Escherichia coli. Antimicrob Agents Chemother (2008) 52:2929–32.
15
.
Eaves DJ, Randall L, Gray DT, et al. Prevalence of mutations within the quinolone resistant-determining region of gyrA, gyrB, parC and parE and association with antibiotic resistance in quinoone-resistant Salmonella enterica. Antimicrob Agents Chemother (2004) 48:4012–5.
16 . Hanahan D. Studies on transformation of Escherichia coli with plasmids. J Mol Biol (1983) 166:557–80.[Web of Science][Medline]
17 . Miller JH. Experiments in molecular genetics. (1972) Cold Spring Harbor, NY: Cold Spring Harbor Laboratory.
18
.
Robicsek A, Strahilevitz J, Sahm DF, et al. qnr prevalence in ceftazidime-resistant Enterobacteriaceae isolates from the United States. Antimicrob Agents Chemother (2006) 50:2872–4.
19 . Carattoli A, Bertini A, Villa L, et al. Identification of plasmids by PCR-based replicon typing. J Microbiol Methods (2005) 63:219–28.[CrossRef][Web of Science][Medline]
20 . García A, Navarro F, Miró E, et al. Acquisition and diffusion of blaCTX-M-9 gene by R478-IncHI2 derivative plasmids. FEMS Microbiol Lett (2007) 271:71–7.[CrossRef][Web of Science][Medline]
21 . Mabilat C, Goussard S, Sougakoff W, et al. Direct sequencing of the amplified structural gene and promoter for the extended-broad- spectrum beta-lactamase TEM-9 (RHH-1) of Klebsiella pneumoniae. Plasmid (1990) 23:27–34.[CrossRef][Web of Science][Medline]
22
.
Poirel L, Cattoir V, Soares A, et al. Novel ambler class A β-lactamase LAP-1 and its association with the plasmid-mediated quinolone resistance determinant QnrS1. Antimicrob Agents Chemother (2007) 51:631–7.
23
.
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.
24
.
Yamane K, Wachino J, Suzuki S, et al. Plasmid-mediated qepA gene among Escherichia coli clinical isolates from Japan. Antimicrob Agents Chemother (2008) 52:1564–6.
25 . Huang Z, Mi Z, Wang C. A novel beta-lactamase gene, LAP-2, produced by an Enterobacter cloacae clinical isolate in China. J Hosp Infect (2008) 70:95–6.[CrossRef][Web of Science][Medline]
26
.
Johnson TJ, Wannemeuhler YM, Scaccianoce JA, et al. Complete DNA sequence, comparative genomics, and prevalence of an IncHI2 plasmid occurring among extraintestinal pathogenic Escherichia coli isolates. Antimicrob Agents Chemother (2006) 50:3929–33.
27 . Hu FP, Xu XG, Zhu DM, et al. Coexistence of qnrB4 and qnrS1 in a clinical strain of Klebsiella pneumoniae. Acta Pharmacol Sin (2008) 29:320–4.[CrossRef][Web of Science][Medline]
28
.
Pezzella C, Ricci A, Di Giannatale E, et al. Tetracycline and streptomycin resistance genes, transposons, and plasmids in Salmonella enterica isolates from animals in Italy. Antimicrob Agents Chemother (2004) 48:903–8.
29
.
Johnson TJ, Wannemuehler YM, Johnson SJ, et al. Plasmid replicon typing of commensal and pathogenic Escherichia coli isolates. Appl Environ Microbiol (2007) 73:1976–83.
30
.
Cavaco LM, Hendriksen RS. Plasmid-mediated quinolone resistance determinant qnrS1 detected in Salmonella enterica serovar Corvallis strains isolated in Denmark and Thailand. J Antimicrob Chemother (2007) 60:704–6.
31
.
Ilyina TV, Koonin EV. Conserved sequence motifs in the initiator proteins for rolling circle DNA replication encoded by diverse replicons from eubacteria, eucaryotes and archaebacteria. Nucleic Acids Res (1992) 20:3279–85.
32
.
García-Fernández A, Cloeckaert A, Bertini A, et al. Comparative analysis of IncHI2 plasmids carrying blaCTX-M-2 or blaCTX-M-9 from Escherichia coli and Salmonella enterica strains isolated from poultry and humans. Antimicrob Agents Chemother (2007) 51:4177–80.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  J. A. Hammerl, J. Beutlich, S. Hertwig, D. Mevius, E. J. Threlfall, R. Helmuth, and B. Guerra pSGI15, a small ColE-like qnrB19 plasmid of a Salmonella enterica serovar Typhimurium strain carrying Salmonella genomic island 1 (SGI1) J. Antimicrob. Chemother., October 27, 2009; (2009) dkp383v1. [Full Text] [PDF]
|
|
|
|
 |
|
 J. Strahilevitz, G. A. Jacoby, D. C. Hooper, and A. Robicsek Plasmid-Mediated Quinolone Resistance: a Multifaceted Threat Clin. Microbiol. Rev., October 1, 2009; 22(4): 664 - 689. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Govender, A. M. Smith, A. S. Karstaedt, K. H. Keddy, and for the Group for Enteric, Respiratory and Meninge Plasmid-mediated quinolone resistance in Salmonella from South Africa J. Med. Microbiol., October 1, 2009; 58(10): 1393 - 1394. [Full Text] [PDF]
|
|
|
|
|
|
D. Fortini, A. Garcia-Fernandez, K. Veldman, D. Mevius, and A. Carattoli Novel genetic environment of plasmid-mediated quinolone resistance gene qnrB2 in Salmonella Bredeney from poultry J. Antimicrob. Chemother., September 29, 2009; (2009) dkp356v1. [Full Text] [PDF]
|
|
|
|
 |
|
 A. M. Dionisi, C. Lucarelli, S. Owczarek, I. Luzzi, and L. Villa Characterization of the Plasmid-Borne Quinolone Resistance Gene qnrB19 in Salmonella enterica Serovar Typhimurium Antimicrob. Agents Chemother., September 1, 2009; 53(9): 4019 - 4021. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Carattoli Resistance Plasmid Families in Enterobacteriaceae Antimicrob. Agents Chemother., June 1, 2009; 53(6): 2227 - 2238. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||