Effect of Chlortetracycline on Salmonella and the Fecal Flora of Swine

POSTER PRESENTATIONs Anatum (16.1 %, 9 farms) followed by Rissen (14.5 %, 7 farms), Typhimurium (11.3 %, 7 farms), Derby (9.7 %, 3 farms), Tilburg (8.1 %, 2 farms), Goldcoast (8.1 %, 1 farm), Typhimurium variant 4,5,12:i:(6.5 %, 4 farms). Serotypes Bovismorbificans, Bredeney, Diarizonae, Grumpensis, Infantis, Kapemba, Kedougou, Ohio, Seftenberg and Virchow were also isolated although less than three times each. Antimicrobial susceptibility analysis showed that the highest level of resistance was against tetracycline (68.8 %). Sulphonamides and their combination with trimethoprim were only active against 67.7 % and 53.1 % of the strains, respectively. Regarding b-lactams, 41.6 % of the strains were resistant to ampicillin and 18.7 % were resistant to the combination of amoxycillin and clavulanic acid. Finally, 17.7 % of strains were resistant to cloramphenicol. Sixty-two percent of the strains showed resistance to three or more antimicrobial agents and 46 % were resistant to five or more drugs. The maximum number of compounds to which one strain was resistant was 10 (corresponding to a 4,5,12:i:strain. In addition 3 strains were resistant to eight or nine compounds. None of the strains was resistant to colistin or ceftriaxone and 12 strains were susceptible to all antimicrobial agents tested (serotypes Anatum, Goldcoast, Kapemba and Ohio). These results indicate that sub-clinical infection with Salmonella can be produced by multi-drug resistant strains. In addition, with very few exceptions, most of the detected serotypes were able to be resistant to more than three drugs. This fact suggests that antimicrobial resistance in Salmonella isolates from pigs is not an exclusive property of a given serotype, for instance Typhimurium, but a widespread characteristic. However, the wider spectrum of resistance is usually found in the 4,5,12:i:variants of Typhimurium (De la Torre et al., 2002). Taking together, these results show that antimicrobial resistance is a real problem in swine isolates of Salmonella and reinforce the notion than an improved knowledge of the impact of antimicrobial agents used in swine is required.