JAC Advance Access originally published online on February 8, 2007
Journal of Antimicrobial Chemotherapy 2007 59(4):815-816; doi:10.1093/jac/dkl559
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Correspondence |
Occurrence and current frequency of CTX-M-type ß-lactamases from a regional hospital in the South West of England
1 Faculty of Medicine, University of Bristol, Bristol BS8 1TD, UK 2 Department of Medical Microbiology, Southmead Hospital, Westbury-on-Trym, Bristol BS10 5NB, UK 3 School of Medicine, Department of Medical Microbiology, Cardiff University, Cardiff CF14 4XN, UK
* Corresponding author. Tel: +44-2920744725; Fax: +44-2920742161; E-mail: walshtr{at}cardiff.ac.uk
Keywords: extended-spectrum , ß-lactamases , mobile genes , ß-lactam resistance
Several papers have recently reported the growing incidence of extended-spectrum ß-lactamases (ESBLs) among Enterobacteriaceae in the UK, not least those of the CTX-M-like genotype.1–4 The UK dominant genotypes appear to be mainly CTX-M-14 and CTX-M-15, although CTX-M-26 and CTX-M-9 have also been reported. The gene encoding the enzyme CTX-M-15, is often carried on a plasmid and flanked by the insertion element ISEcp1, which has been shown to mobilize itself and adjacent DNA.5 Concerned by the growing ESBL rate in a South West Regional Hospital, we genetically analysed and typed both outpatient and nosocomial Escherichia coli strains from a random group of urinary tract (UT) isolates for carriage of blaCTX-M genes. MICs were determined according to the standard BSAC guidelines.6 blaCTX-M genes were amplified and sequenced using previously described primers based on the gene and also its adjacent sequence ISEcp1.5
Of the 33 E. coli UT isolates, 23 possessed blaCTX-M-15 (70%) and these were genetically linked to ISEcp1. All E. coli (n = 10) isolated from urinary catheters possessed blaCTX-M-15, whereas only 13 of 23 outpatient isolates possessed this genotype. Interestingly, none were of the blaCTX-M-9 or blaCTX-M-14 genotypes that have been reported elsewhere in the UK.7 A subset (n = 10) of the positive isolates were further analysed by investigating whether the gene was plasmid or chromosomally mediated by standard plasmid isolation protocols,8 followed by PCR analysis. Oligonucleotides targeted to gyrA were used as a PCR negative/positive control for plasmid/chromosome determination. All blaCTX-M-15 genes were located on plasmids. The plasmids were further analysed by restriction profiling and shown to be identical with an estimated size of 
90 kb (data not shown). Typing (RAPD) on the same 10 isolates indicated that they are not identical, suggesting that the plasmid and not the host strain is the common source of blaCTX-M-15.
The rapid escalation of ESBL in Enterobacteriaceae and, in particular, blaCTX-M genotypes have led to speculation as to their origin and when they first appeared in the UK. A recent report by Hopkins et al.1 records the earliest appearance of blaCTX-M-15 in the UK as May 2001. The gene was carried on an 82 kb plasmid possessing an I1 replicon and found in an E. coli strain of human origin. Given the high frequency of CTX-M-15-positive E. coli in this area, we systematically screened several hundred E. coli isolates back to 1990 and analysed these for ESBL phenotypes and a subset of 34 were genetically screened for carriage of blaCTX-M and ISEcp1.
The earliest isolate from this survey found to be carrying blaCTX-M-15 was from July 2000—some 10 months prior to that reported by Hopkins et al. The gene was plasmid-mediated and possessed the hallmark ISEcp1 element. The patient in question was an elderly lady of Indian origin who had recently visited India in 1999. She was admitted to ICU with an infected abscess and from three consecutive catheter tips grew a pure growth of E. coli. It has been documented that blaCTX-M-15 was widespread in India prior to 2000 and reported in high levels from ESBL-positive Klebsiella pneumoniae, Salmonella spp. as well as E. coli.9 Accordingly, it is reasonable to conclude that this isolate was part of the patient's endogenous normal flora and that the occurrence of these genotypes in the UK has originated elsewhere, rather than resulting from a native environmental/clinical source. The data in this article, coupled with previous UK ESBL studies, confirm that CTX-M-15 is indeed widespread and has become the dominant ESBL in the UK.
We have not received any personal financial payments from any external body that is relevant to the body of information contained within this article.
Acknowledgements
We wish to thank the following scientists for their contributions to these studies: D. M. C. Bennett, K. Bowker and M. A. Toleman.
References
1 Hopkins KL, Batchelor MJ, Liebana E, et al. (2006) Characterisation of CTX-M and AmpC genes in human isolates of Escherichia coli identified between 1995 and 2003 in England and Wales. Int J Antimicrob Agents 28:180–92.[CrossRef][Web of Science][Medline]
2
Woodford N, Kaufmann ME, Karisik E, et al. (2007) Molecular epidemiology of multi-resistant Escherichia coli isolates from community-onset urinary tract infections in Cornwall, England. J Antimicrob Chemother 59:106–9.
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Livermore DM and Hawkey PM. (2005) CTX-M: changing the face of ESBLs in the UK. J Antimicrob Chemother 56:451–4.
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Woodford N, Ward ME, Kaufmann ME, et al. (2004) Community and hospital spread of Escherichia coli producing CTX-M extended-spectrum ß-lactamases in the UK. J Antimicrob Chemother 54:735–43.
5
Poirel L, Lartigue MF, Decousser JW, et al. (2005) ISEcp1B-mediated transposition of blaCTX-M in Escherichia coli. Antimicrob Agents Chemother 49:447–50.
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Andrews J. (2006) BSAC standardized disc susceptibility testing method (version 5). J Antimicrob Chemother 58:511–29.
7
Munday CJ, Whitehead GM, Todd NJ, et al. (2004) Predominance and genetic diversity of community- and hospital-acquired CTX-M extended spectrum ß-lactamases in York, UK. J Antimicrob Chemother 54:628–33.
8 Karim A, Poirel L, Nagarajan S, et al. (2001) Plasmid-mediated extended-spectrum ß-lactamase (CTX-M-3-like) from India and gene association with insertion sequence IS. Ecp1. FEMS Microbiol Lett 201:237–41.
9 Toleman MA, Beidenbach D, Jones RN, et al. (2002) Molecular characterisation of ß-lactamases from Escherichia coli isolated from a multi-centre trial in India: benchmark report from the MYSTIC program. Abstracts of the Forty-second Interscience Conference on Antimicrobial Agents and ChemotherapySan Diego, CA(American Society for Microbiology, Washington, DC, USA) pp. 114 Abstract C2-1872.
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