Characterization of erythromycin resistance in Campylobacter coli and Campylobacter jejuni isolated from pig offal in New Zealand S.A. Harrow 1 , B.J. Gilpin 2 and J.D. Klena 1 1 Department of Plant and Microbial Sciences, University of Canterbury, Christchurch, and 2 Institute of Environmental Science and Research (ESR) Ltd, Christchurch, New Zealand 2003/0273: received 3 April 2003, revised 14 December 2003 and accepted 3 March 2004 ABSTRACT S.A. HARROW, B.J. GILPIN AND J.D. KLENA. 2004. Aims: To determine the level and mechanism(s) of antimicrobial resistance in Campylobacter isolates obtained from human and environmental sources from South Canterbury, New Zealand. Methods and Results: A total of 251 Campylobacter isolates were tested for susceptibility to ciprofloxacin, erythromycin, nalidixic acid and tetracycline using disc diffusion assays. Five pig offal isolates were observed to be highly erythromycin resistant, with minimal inhibitory concentrations determined to be ‡256 lg ml )1 . Nucleotide sequencing of the 23S ribosomal DNA (rDNA) in these resistant isolates identified an A fi G change at Escherichia coli position 2059 that has been previously implicated in erythromycin resistance in Campylobacter coli. Macrorestriction profiling using pulsed-field gel electrophoresis showed these isolates were nonclonal. Conclusions: The majority of Campylobacter isolates from South Canterbury remain sensitive to the most clinically relevant antimicrobial agents. Our results support other reports showing that specific variations in the 23S rDNA contribute to erythromycin resistance. Significance and Impacts of the Study: This study defines the baseline frequency of antimicrobial resistance associated with Campylobacter isolates from South Canterbury, and discusses the likely molecular mechanisms conferring erythromycin resistance in this organism. Resistance to erythromycin in these isolates is not linked to a dominant Campylobacter clone and has likely arisen independently in different genetic lines exposed to selective antimicrobial pressure. Keywords: 23S rDNA, Campylobacter, erythromycin resistance, New Zealand, pigs. INTRODUCTION Campylobacteriosis is the most frequently notified commu- nicable disease in New Zealand (Sneyd and Baker 2003), with an estimated economic cost of NZ$61Æ7 million in 1999 (Scott et al. 2000). Campylobacter enteritis is generally a self- limiting illness, and patients usually recover without the need for antimicrobial therapy. However, in patients with prolonged illness, antimicrobial therapy involving macro- lides (e.g. erythromycin) or fluoroquinolones (e.g. ciprofl- oxacin) may be necessary (Aarestrup et al. 1997). Until recently, a number of clinical antimicrobial agents were also licensed for agricultural and veterinary use in New Zealand. For example, therapeutics containing the macrolides tylosin and tiamulin as active ingredients was licensed in New Zealand until May 2002 for use in pigs (Agricultural Compounds and Veterinary Medicines Group 2000; Mead- ows 2000). These therapeutics were administered to pigs to increase or maintain weight gain, improve feed efficiency, Present address: J.D. Klena, School of Molecular Biosciences, Washington State University, 406 Abelson Hall, Pullman, WA 99164, USA. Correspondence to: S.A. Harrow, New Zealand Institute of Crop and Food Research Ltd, Private Bag 4704, Christchurch, New Zealand (e-mail: harrows@crop.cri.nz). ª 2004 The Society for Applied Microbiology Journal of Applied Microbiology 2004, 97, 141–148 doi:10.1111/j.1365-2672.2004.02278.x