JAC Advance Access published online on September 8, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn380
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Original research |
UK epidemic Escherichia coli strains A–E, with CTX-M-15 β-lactamase, all belong to the international O25:H4-ST131 clone
1 Department of Medical Microbiology, School of Medicine, University of Manchester, Clinical Sciences Building, Manchester Royal Infirmary, Manchester M13 9WL, UK 2 Health Protection Agency North West Laboratory, Clinical Science Building, Manchester Royal Infirmary, Manchester M13 9WZ, UK 3 Health Protection Agency, Centre for Infections, 61 Colindale Avenue, London NW9 5EQ, UK 4 The Microbiology Department, Stepping Hill Hospital, Poplar Grove, Hazel Grove, Stockport NHS Foundation Trust, Stockport SK2 7JE, UK 5 Preston Microbiology Services, Royal Preston Hospital, Lancashire Teaching Hospitals NHS Foundation Trust, Sharoe Green Lane, Preston, Lancashire PR2 9HT, UK
* Corresponding author. Tel: +44-161-276-8828; Fax: +44-161-276-8826; E-mail: mat.upton{at}manchester.ac.uk
Received 30 June 2008; accepted 13 August 2008
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Abstract |
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Objectives: Uropathogenic and invasive Escherichia coli O25:H4-ST131 isolates producing CTX-M-15 extended-spectrum β-lactamase (ESBL) enzymes have recently been shown to be disseminated across the globe. In the UK, many CTX-M-15 ESBL-producing E. coli strains have been previously defined as belonging to the epidemic strains A–E, as determined by PFGE. The present study was carried out to define the relationship between these two groups of pathogenic E. coli.
Methods: Multilocus sequence typing and PFGE were used for molecular characterization of a collection of 61 ESBL-producing E. coli isolates from across the UK.
Results: Strains A to E all belonged to the ST131 clone, further underscoring the epidemiological importance of this lineage.
Conclusions: The future spread of the ST131 clone, and its UK variants, should be monitored closely and the pathogenic mechanisms explaining their success should be investigated.
Key Words: multilocus sequence typing , MLST , molecular epidemiology , uropathogenic Escherichia coli , UPEC , extended-spectrum β-lactamases , PFGE
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Introduction |
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Escherichia coli is one of the two most common causes of bacteraemia in England and Wales1 and causes the majority of urinary tract infections (UTIs) worldwide. The widespread use of antibiotics has selected for drug-resistant strains, with current concern centred on those with fluoroquinolone resistance and extended-spectrum β-lactamases (ESBLs). ESBL-producing E. coli—principally with CTX-M-type enzymes, particularly CTX-M-15—increasingly cause UTIs in the community and long-term care and hospital settings in the UK.2,3 Five major epidemic E. coli strains (A–E) with CTX-M-15 β-lactamase were identified in the UK, based on their PFGE banding patterns, along with many clonally diverse producers of the enzyme. Epidemic strain A is nationally distributed, being particularly dominant in parts of Lancashire, Shropshire, Hampshire and Ulster.2
Most strain A–E isolates are resistant to oxyimino-cephalosporins and, through co-production of OXA-1 β-lactamase, also to β-lactamase inhibitor combinations; in addition, most isolates are resistant to fluoroquinolones, trimethoprim, tetracyclines and amikacin. Strain A is susceptible to gentamicin, the others are generally resistant. A few strain A isolates in the north-west (NW) of England possess plasmid-mediated AmpC β-lactamase and consequently have enhanced resistance to cephamycins and cephalosporin/β-lactamase inhibitor combinations.4
This rise in E. coli with CTX-M enzymes is not unique to the UK and several recent studies using multilocus sequence typing (MLST) have identified a globally disseminated O25:H4-ST131 clone with CTX-M-15 β-lactamase, causing significant morbidity and mortality.5–7 The aim of the work presented here was to study the genetic relationship of the UK epidemic strains A–E, which are known to be serotype O25, with the international O25:H4-ST131 E. coli lineage.
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Materials and methods |
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Bacterial isolates
Thirty-two E. coli isolates with CTX-M β-lactamases were selected from among those referred to the Health Protection Agency Antibiotic Resistance Monitoring and Reference Laboratory (ARMRL) from UK centres: 24 had previously been assigned to the UK epidemic lineages A–E based on PFGE; the remaining eight were diverse. These 32 isolates were compared, using MLST and PFGE, with 29 E. coli isolates that had been previously reported as part of a larger group from the NW region of England.6 These latter 29 isolates comprised 10 E. coli from hospital A and 19 from hospital B (Table 1) and were chosen to represent the diversity of sequence types (STs) circulating in the region, with ST131 dominating.6 They were recovered from separate patients with UTI, between November 2004 and October 2005.6
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Typing of isolates
Isolation of DNA and MLST analysis were performed as described previously.6 Isolates were also compared by PFGE separation of XbaI-digested genomic DNA, as described previously.8 Profiles were compared using Bionumerics software (Applied Maths, Sint-Martens-Latem, Belgium).
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Results |
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Characterization of E. coli isolates by MLST
MLST analysis identified 12 different STs among the total of 61 isolates studied (Table 1); of these 12 STs, 10 occurred only once in the data set and 2 (ST683, ST684) were novel.
Among the 32 isolates referred to ARMRL, all of the 24 previously assigned by PFGE to the five major UK epidemic strains (A–E) belonged to ST131, as did 2 further isolates, distinct by PFGE. The remaining six strains from the ARMRL collection, all with distinct PFGE patterns, belonged to STs unrelated to ST131 (Table 1).
Among the 29 isolates from NW England, the predominant lineage was ST131; all of the 10 isolates from hospital A were identified as ST131, as were 12/19 among those from hospital B.
PFGE characterization of E. coli isolates
PFGE was performed on the 29 isolates from NW England. All of the 10 ST131 E. coli isolates from hospital A, 7 of them with both AmpC and group 1 CTX-M enzymes, had the PFGE profile characteristic of the UK epidemic strain A (Table 1). The 12 ST131 isolates from hospital B comprised two distinct PFGE types (2 and 3) (Table 1 and Figure 1). The seven non-ST131 isolates from hospital B showed unique PFGE profiles within this data set (Table 1); six of these are shown in Figure 1.
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Discussion |
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The global rise of E. coli producing CTX-M β-lactamases, principally CTX-M-15, as agents of UTIs, often has major public health implications.3 In the UK, this rise became apparent from 2003 when it was recognized that, aside from many diverse producers, there were five major strains (A–E) defined by PFGE. Members of these strains were more closely related to each other than diverse producers and all were of serotype O25.
The use of MLST in the present study showed that the UK epidemic strains A–E clustered with the globally disseminated O25:H4-ST131 lineage already reported from Europe, Africa, Asia and North America.5–7 It was also shown that the previously reported ST131 isolates from NW England, some of them with both AmpC and group 1 CTX-M enzymes, belonged to the PFGE-defined strain A.
The finding that isolates of ST131 encompassed multiple PFGE profiles, including the A–E lineages as well as other minor types, suggests that genomic diversification has occurred within this lineage, presumably reflecting DNA rearrangements, mutations and the integration of insertion sequences and other mobile elements. The reported diversity in virulence determinants carried by ST131 isolates5,9 further supports the suggestion of genomic plasticity, though it is possible that some of these factors may be encoded by extrachromosomal DNA. Nevertheless, although recombination is occurring in this lineage, it has not resulted in breakdown of the clonal structure.
MLST provides a robust and relatively simple means of unambiguously defining the relatedness of E. coli clones, though additional analyses, including PFGE, may be useful for increasing discrimination within lineages. Moreover, many antibiotic resistance genes in these strains are carried on plasmids, which have been shown to vary within and between different lineages.10 Further characterization of plasmids encoding CTX-M-15 enzymes in ST131 and non-ST131 hosts is likely to be informative and should be employed for a deeper understanding of the genetic relationships among these E. coli strains. In addition, a full investigation of the antibiotic and virulence determinants carried by representatives of the O25:H4-ST131 lineage should be a priority for those concerned with the disease caused by this widely disseminated organism. Such full characterization of these antibiotic-resistant E. coli clones may facilitate development of intervention and prevention strategies to control their spread in community and hospital environments.
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Funding |
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S. H. L. is in receipt of a Health Protection Agency-funded PhD studentship. No funding for the work was required, other than that supplied for the PhD studentship awarded to S. H. L.
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Transparency declarations |
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D. M. L. and N. W. have received research grants and speaking invitations from various pharmaceutical companies. D. M. L. has a diversified share portfolio. None of these poses a conflict of interest with this work. Other authors have nothing to declare.
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Acknowledgements |
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We would like to thank local microbiology laboratories for submitting isolates to the study. This publication made use of the Escherichia coli MLST website (http://web.mpiib-berlin.mpg.de), sited at the Max Planck Institute für Infektionsbiologie.
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References |
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1 . Health Protection Agency. Trends in Antimicrobial Resistance in England and Wales, 2004–2005 (2006) London, UK: HPA. http://www.hpa.org.uk/webw/HPAweb&HPAwebStandard/HPAweb_C/1196942165725?p=1158945066450.
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Woodford N, Ward ME, Kaufmann ME, et al. Community and hospital spread of Escherichia coli producing CTX-M extended-spectrum β-lactamases in the UK. J Antimicrob Chemother (2004) 54:735–43.
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Livermore DM, Canton R, Gniadkowski M, et al. CTX-M: changing the face of ESBLs in Europe. J Antimicrob Chemother (2007) 59:165–74.
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Woodford N, Reddy S, Fagan EJ, et al. Wide geographic spread of diverse acquired AmpC β-lactamases among Escherichia coli and Klebsiella spp. in the UK and Ireland. J Antimicrob Chemother (2007) 59:102–15.
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Clermont O, Lavollay M, Vimont S, et al. The CTX-M-15-producing Escherichia coli clone belongs to a highly virulent B2 phylogenetic subgroup. J Antimicrob Chemother (2008) 61:1024–8.
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Lau SH, Reddy S, Cheesbrough J, et al. A major uropathogenic Escherichia coli strain identified in the North West of England by multilocus sequence typing. J Clin Microbiol (2008) 46:1076–80.
7 . Coque TM, Novais A, Carattoli A, et al. Dissemination of clonally related Escherichia coli strains expressing extended-spectrum β-lactamase CTX-M-15. Emerg Infect Dis (2008) 14:195–200.[Web of Science][Medline]
8 . Kaufmann ME. Pulsed-field gel electrophoresis. In: Molecular Bacteriology: Protocols and Clinical Applications—Woodford N, Johnson AP, eds. (1998) Totowa, NJ, USA: Humana Press.
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Karisik E, Ellington MJ, Livermore DM, et al. Virulence factors in Escherichia coli with CTX-M-15 and other extended-spectrum β-lactamases in the UK. J Antimicrob Chemother (2008) 61:54–8.
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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.
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