Antimicrobial resistance in Escherichia coli isolates from turkeys and hens in Ireland

Martin Cormicana,*, Victoria Buckleya, Geraldine Corbett-Feeneya and Fergal Sheridanb

a Department of Bacteriology, National University of Ireland, Galway; b Monaghan Veterinary Laboratory Ltd, Clones Road, Monaghan, Ireland

Sir,

We read with interest the paper by van den Bogaard and colleagues1 relating to the antimicrobial susceptibility of Escherichia coli isolates from poultry. Since September 2000 we have been studying the antimicrobial susceptibility of E. coli isolated as pathogens from poultry flocks in two counties in Ireland. Isolates were obtained on culture of tissues or swabs from diseased or dead animals and referred to the Department of Bacteriology, National University of Ireland, Galway, for antimicrobial susceptibility testing. The identity of the isolates as E. coli was confirmed by API20E and antimicrobial susceptibility testing was performed by the disc diffusion method of the NCCLS.2 Susceptibility to 13 antimicrobial agents (TableGo) was determined, using E. coli ATCC 25922 as control. For isolates categorized as intermediate or resistant to ciprofloxacin by initial disc diffusion susceptibility testing, the ciprofloxacin MIC was determined by Etest.


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Table. Percentages of E. coli isolates from turkey and hens susceptible (S), intermediate (I) and resistant (R) to antimicrobial agents by NCCLS disc diffusion methods
 
A total of 209 isolates of E. coli have been examined, 171 isolates from turkeys and 38 from hens (broiler and egg layers). The percentage of isolates susceptible, intermediate and resistant to each antimicrobial agent is outlined in the TableGo. The ciprofloxacin MIC for the five ciprofloxacin-resistant isolates was in the range 6 to 16 mg/L.

Like van den Bogaard et al.,1 we observed a trend towards higher levels of antimicrobial resistance in turkeys, in which antimicrobial use is more common. Resistance to sulphonamides, trimethoprim and nalidixic acid were more common in E. coli originating from turkeys, and ciprofloxacin resistance, albeit at a low level of 2.9%, was observed only in E. coli isolates from turkeys.

Our data differ from those of van den Bogaard et al.1 in a number of respects. The isolates were considered patho-genic and susceptibility test methods and interpretative criteria used were those of the NCCLS. For the purpose of analysis we have grouped all hens together rather than distinguishing between broilers and egg layers. Consideration of these as one group reflects the fact that antimicrobial agents are used infrequently in hens in these flocks (egg producer or broilers), but somewhat more commonly in turkeys because of a greater frequency of infectious disease problems during the longer production cycle. The agents used in treatment of infection in turkeys were formerly tetracycline and more recently potentiated sulphonamides. Chloramphenicol and aminoglycosides are not used in these flocks of hens or turkeys. There are significant economic disincentives to the use of fluoroquinolone agents where older agents are effective. Nevertheless increased use of enrofloxacin has come about in the past 4 years because of problems in the management of bacterial infection in turkeys, in particular bacterial infections that are secondary to the recently introduced viral infection turkey rhinotracheitis.

It is important to recognize the limitations of our data. The species of animal from which the E. coli are derived are quite different in many respects and the production cycles are quite distinct. Nevertheless there is some evidence of a relationship between levels of antimicrobial resistance in E. coli and the requirement for antimicrobial use in existing production systems for the species from which the isolates derive. These results relate to flocks in which antibacterial growth promoters are not used and an all-in/all-out production cycle with terminal cleaning and disinfection is in operation. All antimicrobial use is under veterinary supervision. Even with such controls in place, levels of resistance to antimicrobial agents are high, particularly in E. coli isolates from turkeys, emphasizing the need for continuing close supervision of use of antimicrobial agents in animal production, for ongoing monitoring of antimicrobial resistance in E. coli isolates from production facilities and for research to identify new ways to minimize antimicrobial use in animal production.

Acknowledgements

The authors gratefully acknowledge the support and advice of Mr Donal McLoone.

Notes

* Corresponding author. Tel: +353-91-544146; Fax: +353-91-524216; E-mail: martin.cormican{at}bsi.ie Back

References

1 . van den Bogaard, A. E., London, N., Driessen, C. & Stobberingh, E. E. (2000). Antibiotic resistance of faecal Escherichia coli in poultry, poultry farmers and poultry slaughterers. Journal of Antimicrobial Chemotherapy 47, 763–71.[Abstract/Free Full Text]

2 . National Committee for Clinical Laboratory Standards. (2000). Performance Standards for Antimicrobial Disk Susceptibility Tests—Seventh Edition: Approved Standard M2-A7. NCCLS, Wayne, PA.