1 Nuffield Department of Clinical Laboratory Sciences, Oxford University, Level 7 John Radcliffe Hospital, Oxford OX3 9DU, UK; 2 Department of Microbiology, Level 7 John Radcliffe Hospital, Oxford Radcliffe Hospitals NHS Trust, Oxford OX3 9DU, UK
Keywords: antibiotic resistance , epidemiology , Campylobacter
Sir,
We read with interest the report of increasing erythromycin resistance in Campylobacter isolated from humans in Northern Ireland.1 We have been monitoring antimicrobial resistance in Campylobacter of human origin in Oxfordshire since 1991,2 and our findings differ from those of Rao et al.1 in several respects.
Our laboratory serves a relatively stable population of around 600 000. About 60% of stools received for culture are from patients visiting their general practitioner (GP), and the rest are from hospital inpatients. Approximately 13 000 stool samples are submitted each year, ranging from 10441 in 1991 to 14070 in 2000. The proportion of stools from which a Campylobacter sp. was isolated has followed broadly the total number of stools submitted (Figure 1). A Campylobacter sp. was cultured from 5.7% of stools submitted since 2000, with 637904 isolations in each of the last 5 years. Peak incidence was 150 cases per 100 000 population in 2000, an attack rate three times greater than in Northern Ireland. Such a disparity could be due to differences in the rate of Campylobacter gastroenteritis, sampling thresholds by GPs or laboratory methodology. As in Northern Ireland, the number of Campylobacter isolations in Oxfordshire has decreased since 2000 (Figure 1). This is consistent with national observations, total UK Campylobacter isolations peaking in 2000.3
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Rao et al.1 speculate that the increasing erythromycin resistance seen in human isolates in Northern Ireland is linked to a similar increase in isolates from local poultry. In our previous report we speculated that the widespread use of fluoroquinolones in the poultry industry was a likely cause of the emergence of ciprofloxacin-resistant Campylobacter in human infections.2 Humphrey et al.5 recently reported the rapid emergence of almost 100% ciprofloxacin resistance among Campylobacter during treatment of commercial broiler flocks with difloxacin or enrofloxacin. High resistance rates persisted for up to 4 weeks post-treatment, which was noted as an important observation in relation to the entry of resistant strains into the food chain.
Multilocus sequence typing (MLST) data have demonstrated that Campylobacter jejuni undergoes frequent horizontal exchange of genetic material.6 Such recombination provides a mechanism, in addition to the de novo generation of point mutations, for the rapid horizontal spread of DNA conferring antimicrobial-resistant phenotypes. The selection pressures caused by widespread fluoroquinolone use in food animals and birds colonized by Campylobacter is a possible mechanism driving the continuing increase in ciprofloxacin resistance in Campylobacter causing human infections. MLST data allow the C. jejuni population structure to be defined in terms of clonal complexes,6 some of which appear to be associated with particular host species. Such data from isolates representing different potential sources of human infection (http://pubmlst.org/campylobacter/) may ultimately allow us to understand the routes by which antibiotic-resistant strains are entering the food chain, and explain regional differences such as those reported above.
References
1.
Rao D, Rao JR, Crothers, E et al. Increased erythromycin resistance in clinical Campylobacter in Northern Irelandan update. J Antimicrob Chemother 2005; 55: 3956.
2. Bowler ICJW, Connor M, Lessing, MP et al. Quinolone resistance and Campylobacter species. J Antimicrob Chemother 1996; 38: 315.[ISI][Medline]
3. Health Protection Agency. http://www.hpa.org.uk/infections/topics_az/campy/data_ew.htm (15 February 2005, date last accessed).
4.
The Campylobacter Sentinel Surveillance Scheme Collaborators. Ciprofloxacin resistance in Campylobacter jejuni: casecase analysis as a tool for elucidating risks at home and abroad. J Antimicrob Chemother 2002; 50: 5618.
5.
Humphrey TJ, Jorgensen F, Frost JA et al. Prevalence and subtypes of ciprofloxacin-resistant Campylobacter spp. in commercial poultry flocks before, during, and after treatment with fluoroquinolones. Antimicrob Agents Chemother 2005; 49: 6908.
6.
Dingle KE, Colles FM, Wareing DR et al. Multilocus sequence typing system for Campylobacter jejuni. J Clin Microbiol 2001; 39: 1423.
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