210 ORAL PRESENTATIONS SafePork 2005 ANTIMICROBIAL RESISTANCE IN SALMONELLA STRAINS FROM FATTENING PIGS AND SOWS Nathalie Nollet* 1,2 , Kurt Houf 1 , Jeroen Dewulf 2 , Boudewijn Catry 2 , Lieven De Zutter 1 , Aart de Kruif 2 , Dominiek Maes 2 1 Department of Veterinary Public Health and Food Safety, 2 Department of Reproduction, Obstetrics and Herd Health, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, B-9820 Merelbeke, Belgium Abstract The prevalence of antibiotic resistance and of different resistance patterns for Salmonella isolates collected from sows, from fattening pigs at different ages and at slaughter was determined. All 901 isolates were submitted to antimicrobial susceptibility testing for 14 com- pounds using the disk agar diffusion test. Overall, 50.9% of the strains were resistant to at least 1 antimicrobial agent. The highest per- centage of resistance was found to oxytetracycline (34.2%), streptomycin (32.5%), sulphamethi- zole (27.6%) and ampicillin (24.9%). Multiresistance (resistance2 antimicrobials) was observed in 33.2% of the strains. A significant lower proportion (p<0.01) of resistant strains was recovered in faecal samples from sows than from fattening pigs during the weaning, growing and finishing peri- od. When designing antimicrobial resistance surveillance programmes for Salmonella in pigs, it is important to take multiple samples within each herd from fattening pigs at different time points. Introduction The major sources for human salmonellosis, one of the most occurring foodborne infections, are eggs, poultry meat and pork. In Belgium, 11.065, 10.075 and 12.894 human cases were reported in 2001, 2002 and 2003, respectively (NRSS, 2003). Further identification revealed that each year, S. Enteritidis (64.2, 63.5 and 71.4%, respectively) was the most common serotype isolated, followed by S.Typhimurium (21.4, 24.2 and 19.5%, respectively) In addition to gastrointestinal disorders, there is the hazard of therapeutic failure due to antimicrobial resistance of the causative Salmonella strains. In Belgium, an antimicrobial drug sur- veillance programme has been launched by the National Reference Centre for Salmonella and Shigella since 2000 (Wybo et al., 2004). Recent data showed that approximately 40% of the human Salmonella Typhimurium isolates were resistant to four or more antimicrobial agents (Wybo et al., 2004). Antimicrobial agents are frequently used in the pig industry and pork is the most frequently consumed meat species in Belgium (NIS, 2005). Therefore, Salmonella contaminated pork may be an important vector for transmitting microbial resistant Salmonella strains to humans. Currently, only limited data about antibiotic resistance in Salmonella isolates from pigs is available. The aims of the present study were to determine the occurrence of antibiotic resistance in Salmonella iso- lates collected from sows, nursery, growing and finishing pigs. The occurrence of different resist- ance patterns was additionally investigated. Materials and Methods All 901 samples originated from 2 field studies that were conducted dur- ing 2001-2002 (Nollet et al., 2004) and 2003-2004 (Nollet et al., 2005), respectively. During study 1, 1821 mesenteric lymph node samples were collected of which 1066 were Salmonella positive. From the 1066 isolates, 527 were selected at random (using random tables) to be tested for their antimicrobial susceptibility. In study 2, faecal samples were taken individually from sows during one production cycle and from pigs during the nursery (5-11 weeks of age), growing (12-18 weeks of age) and finishing period (19-26 weeks of age). The day before pigs were moved to another unit, environmental swabs (overshoes) of that particular unit were taken. In addition, feed sam- ples were gathered at each herd visit. Fifty-six isolates were recovered from the sows; 30, 85 and 52 from the fattening pigs during the nursery, growing and finishing period, respectively, and 86, 34 and 20 isolates from small intestinal content, colon content and mesenteric lymph nodes, respectively. Isolates were serotyped following the Kauffman-White scheme (Popoff and Le Minor, 1992). Only the isolates of study 2 were characterised at strain-level using RAPD and PFGE (Nollet et al., 2005a). To determine the antimicrobial resistance patterns, the disk agar diffusion test was used according to the guidelines established by the National Committee for Clinical Laboratory Standards (NCCLS, 2003). In total, 14 antimicrobial agents were tested. The antibiotic disks (Neo- Sensitab, Rosco, Taastrup, Denmark) used were: amoxycillin/clavulanate (30/15 μg), ampicillin (33 brought to you by CORE View metadata, citation and similar papers at core.ac.uk provided by Digital Repository @ Iowa State University