JAC Advance Access originally published online on January 25, 2008
Journal of Antimicrobial Chemotherapy 2008 61(3):504-508; doi:10.1093/jac/dkm517
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Original research |
Imported chicken meat as a potential source of quinolone-resistant Escherichia coli producing extended-spectrum β-lactamases in the UK
1 Microbiology Laboratory, Shrewsbury and Telford Hospital NHS Trust, Shrewsbury SY3 8XQ, UK 2 Division of Immunity and Infection, The Medical School, University of Birmingham, Birmingham B15 2TT, UK 3 West Midlands Health Protection Agency, Heart of England NHS Foundation Trust, Birmingham B9 5SS, UK 4 Antibiotic Resistance and Monitoring Reference Laboratory, Health Protection Agency, 61 Colindale Avenue, London NW9 5EQ, UK
* Corresponding author. Tel: +44-1743-261163; Fax: +44-1743-261165; E-mail: roderic.warren{at}homecall.co.uk
Received 23 September 2007; returned 4 December 2007; revised 4 October 2007; accepted 5 December 2007
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Abstract |
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Objectives: Escherichia coli producing CTX-M-15 enzyme began to rapidly spread in the UK from around 2003 but other types also occur, notably CTX-M-14. We examined breasts from UK-reared (n = 62) and imported (n = 27) chickens as potential sources of quinolone-resistant E. coli with blaCTX-M genes. A further 40 samples for which the country of rearing could not be identified were examined.
Methods: During 2006, 129 fresh and frozen chicken breast fillets were purchased from retail outlets in the West Midlands. These were cultured for E. coli on CLED agar containing 8 mg/L ciprofloxacin and carrying a 10 µg cefpodoxime disc. Resistant isolates were identified and typed by RAPD fingerprinting; blaCTX-M was identified by PCR and genotyped by reverse-line hybridization.
Results: The country of rearing was identified from the packaging for 89 of 129 purchased samples. Only one of the 62 UK-reared chicken samples carried E. coli producing a CTX-M-1 enzyme, whereas 10 of 27 samples reared overseas had E. coli with CTX-M enzymes. Specifically, 4/10 Brazilian, 3/4 Brazilian/Polish/French, and 2/2 Dutch samples had E. coli with CTX-M-2 enzymes. Six of 40 samples for which the country of rearing was not known had producers of CTX-M enzymes, 5 of them with CTX-M-14.
Conclusions: Quinolone-resistant E. coli with various CTX-M β-lactamase genes that are common in human infections worldwide were found in imported chicken breasts, indicating a possible source for gut colonization. Samples from Brazil were commonly positive for E. coli with CTX-M-2, the dominant blaCTX-M genotype from human infections in South America, which is currently rare in clinical infections in the UK. CTX-M-15, the dominant CTX-M type in human infections in the UK, was not found in chicken isolates, suggesting that the UK-reared chickens are not a reservoir of CTX-M-15.
Keywords: ESBLs , food , quinolones , Enterobacteriaceae
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Introduction |
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Extended-spectrum β-lactamases (ESBLs) are bacterial enzymes that degrade oxyimino-cephalosporins such as cefotaxime and ceftazidime. They are spread among bacterial species by plasmids, often carrying multiple antibiotic resistance genes. Since 2003, multiply-resistant Escherichia coli strains producing the CTX-M-15 type ESBL have become widespread as agents of urinary and other infections in many primary and secondary care centres in the UK. Five closely related clones, all of serotype O25 and phylogroup B2, are common, along with many clonally diverse producers. The increase in CTX-M-15-producing E. coli in the UK in 2003, with the simultaneous multicentric appearance of clonally related strains, is unexplained. A nationally distributed food source cannot be excluded, due to the lack of sampling at the time of onset of the UK outbreak. All the clinical O25 isolates in Shropshire and most of the isolates nationally are also quinolone-resistant by a mechanism independent of ESBL production.1–3 Similar dramatic increases in ESBL-producing E. coli have occurred in many other countries, often associated with community acquisition and the problem has been described as a pandemic.3,4 Plasmid-mediated CTX-M β-lactamase genes originated by mobilization from the genus Kluyvera and subsequent mutation have resulted in the emergence of nearly 50 distinct variants.4 Several of these have a distinct geographical distribution worldwide, e.g. CTX-M2 in South America, Israel and Japan, CTX-M-14 in China, and CTX-M-9/14 in Spain.5 This probably arises from the transfer of blaCTX-M genes from Kluyvera into E. coli and subsequent accumulation of mutations locally followed by widespread distribution at these locations. CTX-M-15 enzyme occurs worldwide but is the only genotype present in India, which has been suggested as its origin.6 The recognition of genotypes that are rare in the UK but very common in other parts of the world suggests direct/indirect importation, although it could sometimes represent a recurrence of the same mutation.
Food is an important vehicle for antibiotic-resistant gastrointestinal pathogens such as Campylobacter jejuni and Salmonella enterica. S. enterica with CTX-M enzymes are increasingly reported from food animals, particularly poultry, and the genotypes sometimes correspond with the locally dominant human types,7 although this is not always the case.8 Likewise, E. coli strains in food animals in Japan,9 Spain10 and Hong Kong11 tend to carry the same CTX-M enzyme variants locally dominant in human isolates, but food is not confirmed as a human source. It is widely argued that as meat products are cooked, there is little likelihood that antibiotic-resistant bacteria present in the raw material will colonize the human gut. This view is challenged by the work from 30 years ago, which clearly demonstrated the colonization of humans by antibiotic-resistant E. coli in the course of preparing and eating cooked chicken in the home.12 Moreover, there is a substantial overlap between the phylogroups, serotypes and virulence factors of E. coli from human urinary infections and those of poultry strains of E. coli associated with the disease of avian colibacillosis.13,14 E. coli serotype O25 has been isolated from chickens in India,15 where CTX-M-15 was originally described. Raw retail poultry in the USA is frequently reported to contain quinolone-resistant E. coli with human urinary infection virulence factors.16,17 On the basis of these earlier findings, we examined chicken breasts as a potential reservoir of quinolone-resistant ESBL-producing E. coli and tested the hypothesis that the rapid multi-focal proliferation of E. coli with CTX-M-15 β-lactamase might be related to consumption of chicken breast meat currently on sale in the UK.
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Methods |
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During January/February and July/August 2006, 129 fresh and frozen raw chicken breast fillets (originating from the UK and other countries) were purchased by local authority environmental health officers from 18 different retail outlets, including 13 major supermarket chains in Shropshire and Birmingham, UK. Sampling was unstructured and convenience-based. Sampling depended on the number of products available on the day and sought to represent both imported and UK products. Twenty-five grams of the chicken meat was macerated with 225 mL of buffered peptone water (Oxoid, Basingstoke, Hants, UK) and incubated for 18 h at 37°C. Ten microlitre aliquots of the broth cultures were then plated onto CLED agar (Oxoid) containing 8 mg/L ciprofloxacin, and a cefpodoxime disc (10 µg) was placed on the agar surface. This recovery method was insensitive as it did not involve selective liquid enrichment and was primarily selective for quinolone-resistant organisms; it would not have grown any that had ESBLs but which remained fluoroquinolone susceptible, although these are uncommon in human isolates in the UK. After incubation, resistant colonies from within the cefpodoxime zone were retained, initially confirmed as E. coli using chromogenic urinary agar (BBL, Oxford, UK), subsequently confirmed as E. coli using API20E identification, and were investigated for ESBL production using the Oxoid combination disc test.18 Isolates found to be ESBL-positive were screened for blaCTX-M by multiplex PCR,14 and reverse-line hybridization was used to identify the specific blaCTX-M genotypes,19 which were then confirmed by sequencing. The clonality of blaCTX-M-bearing isolates was investigated using RAPD genomic fingerprinting.20
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Results |
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Of the 62 packaged raw breasts from chicken reared in the UK, only one yielded a quinolone-resistant E. coli with a blaCTX-M gene, compared with 9 of 27 of those identifiable as reared overseas and 7 of 40 for which the country of rearing was not stated. The UK-reared sample carried E. coli with a CTX-M-1 enzyme. No isolates with CTX-M-15 enzyme were found. However, isolates with CTX-M-2 and CTX-M-14 enzymes were common and single strains producing CTX-M-1 or CTX-M-8 enzymes were recovered (Table 1). Isolates with CTX-M-2 genes were recovered in imports from Brazil (4/10 samples) and 3/4 samples of pooled chicken meat from France, Poland and Brazil, as well as the Netherlands. Isolates with CTX-M-14 and M-8 enzymes were recovered from meat where the country in which the chicken was reared was not indicated on the packaging. Overall, the chicken packaging contained references to 27 cutting/packing stations, but not all indicated the country in which the chicken was reared. Enquiry was made of UK cutting/packing stations to determine the origin from product code numbers, but this information was not always supplied. Coded details of supermarket of origin, retail outlet, cutting/packing station and lot, for all samples yielding positive isolates are given in Table 2. The proportions of samples yielding positive isolates from cutting/packing stations yielding any positives are given in Table 3. Positive results were not related to the presence of skin on the breasts (data not shown). RAPD typing showed that all the blaCTX-M-positive isolates were unique.
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Discussion |
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In contrast to the recent papers from Japan, Hong Kong and Spain reporting poultry carriage of the same CTX-M genotypes of E. coli in food as are locally dominant in human infections,9–11 we did not find a single strain of E. coli with the clinically predominant blaCTX-M-15 genotype.
British poultry yielded only a single strain with a CTX-M enzyme, specifically CTX-M-1 enzyme, which has only recently been reported causing infection in the UK in the West Midlands. This low UK rate may reflect restrained use of antibiotics such as ceftiofur and enrofloxacin in the UK poultry production.
Sixteen more isolates with CTX-M enzymes were found, however, in isolates from imported raw chicken. In particular, 40% of the imported Brazilian chicken and three of four samples with an aggregated origin of ‘Brazil/Poland/France’ contained E. coli producing CTX-M-2 enzyme, as did two chicken samples from the same lot from the Netherlands. The latter finding correlates with a recent Dutch report of blaCTX-M-2 in S. enterica Virchow from broiler faeces.8 CTX-M-2 is rare in human clinical isolates in Europe but well known to be the prevalent CTX-M type in clinical isolates from Argentina, so its isolation from Brazil-reared chicken is unsurprising. The second most frequently encountered genotype was CTX-M-14 from samples packed for two supermarket chains and handled in at least two UK packing/cutting stations but where the country of rearing was not recorded. Originally described in far Eastern countries,21 this type has spread and, together with the related CTX-M-9 type, is now prevalent also in Spain.22 Moreover, both a survey of human faecal carriage in 2003 in York23 and a recent survey24 of strains from human infections found CTX-M-14 to be the second-most-prevalent UK genotype after CTX-M-15.
We hypothesized that chicken products imported into the UK potentially could act as a major source of gut colonization by avian strains of E. coli that carry blaCTX-M ESBL genes. Cooking does not necessarily prevent organisms from raw chicken, handled and cooked in a domestic setting, from colonizing the gut.12 The phylogroups and serotypes of E. coli that cause urinary infection (uropathogenic or extraintestinal pathogenic E. coli) are restricted when compared with avian and human faecal isolates but are similar to avian pathogenic strains of E. coli (APEC).14 The complete genome of an APEC strain was 95.5% identical to a human uropathogenic (UPEC) E. coli strain, and multi-locus sequence typing showed that some human UPEC strains were more similar to APEC than to other human UPEC strains.25 Further, molecular comparisons of multiple virulence and antibiotic resistance factors suggest that human antimicrobial-resistant E. coli more closely resemble poultry strains than human antimicrobial-susceptible E. coli.26 Early in the rise in CTX-M in the UK, data from a survey of faecal colonization showed a much wider range of both genotypes and host species than was then seen among in-patients.23 Introduction of some strains with locally new CTX-M genotypes via imported food may lead to gut colonization that precedes urinary tract infection.27 Differing current food and extraintestinal human genotypes may not preclude subsequent clinical infection with the food genotype. Gut colonization, when followed by urinary catheterization or personal hygiene problems, could explain the current epidemiology of ESBL producers, which occur particularly in the elderly in the UK in hospitals and the community. Ingested avian strains could transfer resistance or virulence factors to human pathogenic E. coli, although this would not explain multi-focal clonal spread. CTX-M-15 has now been described in retail chicken meat in the USA simultaneously with the first descriptions of community human cases with this genotype.28
Although E. coli strains with the dominant CTX-M-15 enzyme were not found in the current meat samples, we cannot discount the possibility that they have (or originally had) a source in foodstuffs. E. coli isolates with CTX-M-15 were recognized from 2001 in the UK, but first became widespread in 2003. A counter-explanation is that strains with CTX-M-15 were introduced by returning travellers or migrants from the Indian subcontinent, where the enzyme is extremely widespread6 and from where it was first described. However, several of the early epicentres of clonal E. coli with CTX-M-15 enzymes (e.g. Ulster and Shrewsbury) do not have large migrant populations, arguing against spread mediated by human travel.
Given the frequent presence of E. coli strains with quinolone resistance and CTX-M genes in raw chicken breast on sale, sustained parallel surveillance of imported raw meat sources and human infection is necessary to establish whether there is a related, gradual change in the prevalent CTX-M types and whether resistance genes and plasmids in isolates from raw food are the progenitors of changes in the epidemiology of CTX-M enzymes in clonal isolates. Packaging information should indicate the country where chicken is reared, and the bacteriological standards for raw poultry meat should be reviewed. The high prevalence of multiresistant ESBL-producing E. coli in imported chicken is undesirable. Although molecular epidemiology did not show that raw poultry meat is an ongoing source for the current clinical infections in the UK, this meat has the potential to act as a source for faecal colonization with ESBL-producing E. coli as a prelude to extraintestinal infection.
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V. M. E. was supported in part for undertaking the molecular work by a grant from the British Society for Antimicrobial Chemotherapy awarded to P. M. H. Analytical work on food samples was supported by internal funding from the Health Protection Agency for the normal food, water and environmental activity of its laboratories and Collaborating Laboratories.
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None to declare.
Contributions to the study: R. E. W., hypothesis, study design and manuscript preparation; P. M. H. and K. N., study design and manuscript preparation; V. M. E., molecular strain determination, data analysis and RAPD; P. O’N., liaison with food liaison groups; M. H., V. B. and J. T., culture and other bacteriology of food samples; D. M. L. and N. W., preliminary molecular analysis and manuscript preparation.
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Acknowledgements |
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These data were presented as a poster at the European Congress of Clinical Microbiology and Infectious Diseases, Munich, 2007. We thank the local authority environmental health officers of the Shropshire and West Midlands Food Liaison Groups for collection of the samples and enquiries on the countries of origin.
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