JAC Advance Access originally published online on May 18, 2004
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Journal of Antimicrobial Chemotherapy (2004) 53, 997-1003
© 2004 The British Society for Antimicrobial Chemotherapy
Trends in antimicrobial resistance, phage types and integrons among Salmonella serotypes from pigs, 1997–2000
Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough Street, Raleigh, NC 27606, USA
Received 25 December 2003; returned 17 February 2004; revised 23 March 2004; accepted 24 March 2004
Objectives: The objectives of this study were to determine antimicrobial resistance and to identify phage types and class 1 integrons among non-typhoidal Salmonella isolates from 24 pig farms in North Carolina collected between 1997 and 2000.
Methods: A total of 1314 isolates of 30 serotypes from pig faecal samples were collected and analysed over a 3 year period. The isolates were characterized using antimicrobial susceptibility testing, phage typing, PCR and DNA sequencing for class 1 integrons.
Results: A high frequency of resistance to antimicrobial agents including tetracycline (85%), ampicillin (47%), co-amoxiclav (23%) and chloramphenicol (21%) was detected. Two multidrug resistance patterns were common in Typhimurium (including variant Copenhagen): isolates with co-amoxiclav, ampicillin, chloramphenicol, streptomycin, sulfamethoxazole and tetracycline (R-type AxACSSuT) [36%] and isolates with ampicillin, kanamycin, streptomycin, sulfamethoxazole and tetracycline (R-type AKSSuT) [45%] resistance patterns. Definitive Type 104 (DT104) was the most common (34%) among eight phage types identified. AKSSuT was found among non-DT104 phage types, particularly DT21 and DT193. Class 1 integrons were detected among various serotypes including Typhimurium, Derby, Muenchen, Worthington, Bere and Muenster. aadA was the most common resistance gene insert, and the oxa30 ß-lactamase resistance gene was also identified among serovar Muenchen.
Conclusions: In this study, two most important multidrug resistance patterns (AxACSSuT and AKSSuT) and phage types of public health significance (DT104 and DT193) constituted two-thirds of the serotype Typhimurium isolates. The findings imply that pigs raised in the commercial production system may pose a risk in serving as reservoirs of resistant Salmonella.
Keywords: swine, food safety, antibiotic resistance, salmonellae
* Corresponding author. Tel: +1-919-513-6141; Fax: +1-919-513-6383; E-mail: wagebrey{at}ncsu.edu
Present address. Department of Clinical and Population Sciences, University of Minnesota, St Paul, MN, USA.
¶ Present address. Department of Veterinary Preventive Medicine, College of Veterinary Medicine, Ohio State University, OH, USA.
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