Ten years of antimicrobial susceptibility testing of Salmonella from Danish pig farms.
OBJECTIVE
This study analysed the trends in antimicrobial resistance in Salmonella serovars and phage types from pigs in Denmark from 1997 to 2006.


METHODS
Salmonella isolates collected through the Salmonella surveillance programme in pigs were serotyped and phage-typed, and susceptibilities to the following antimicrobials were determined: ampicillin, chloramphenicol, gentamicin, nalidixic acid, colistin, streptomycin, sulphonamide, tetracycline and trimethoprim.


RESULTS
No significant development of resistance occurred within the most important serovars, except Salmonella Typhimurium. A major decrease in Salmonella Typhimurium DT12 occurred from 46.5% in 1998 to 16.8% in 2006 while DT120, DT170 and DT104 increased. Throughout the study period, 80.9% of the DT12 isolates remained susceptible to the antimicrobials tested despite an increase in antimicrobial consumption in pigs during the period. In DT120, DT170 and DT104, only 20.1%, 33.1% and 23.0%, respectively, remained fully susceptible.


CONCLUSIONS
The results support that the use of antimicrobial agents might select for multiple resistant clones and that this might be the driver of changes in antimicrobial resistance within a serovar, rather than an emergence of resistance within clones. The results of this study also support that susceptible serovars only slowly become resistant to the antimicrobials tested.
Emborg
Hanne-Dorthe
HD
National Food Institute, Technical University of Denmark, Mørkhøj Bygade 19, DK-2860 Søborg, Denmark. hde@food.dtu.dk
Baggesen
Dorte Lau
DL
Aarestrup
Frank Møller
FM
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001434:Bacteriophage Typing; D003718:Denmark; D024881:Drug Resistance, Bacterial; D008826:Microbial Sensitivity Tests; D012475:Salmonella / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification; D012481:Salmonella Infections, Animal / Q000382:microbiology*; D012703:Serotyping; D013552:Swine; D013553:Swine Diseases / Q000382:microbiology*
D000900:Anti-Bacterial Agents