Effect of a 5 day enrofloxacin treatment on Salmonella enterica serotype Typhimurium DT104 in the pig.
OBJECTIVE
There are concerns that the use of enrofloxacin in livestock production may contribute to the development of fluoroquinolone resistance in zoonotic bacteria. The objective of our study was to investigate the effect of a single 5 day enrofloxacin treatment on Salmonella enterica serotype Typhimurium DT104 in a pig model.


RESULTS
Our results showed that a single treatment failed to eradicate S. Typhimurium DT104, which continued to be isolated up to 35 days after treatment. We also provide evidence that treatment positively selects for S. Typhimurium DT104 strains that are already nalidixic acid resistant (gyrA Asn-87) or cyclohexane resistant, the latter being indicative of an up-regulated efflux pump. Emergence of fluoroquinolone resistance was not detected during treatment or post-treatment in any of the Salmonella strains monitored. However, the effect of enrofloxacin on the nalidixic acid-resistant and cyclohexane-resistant S. Typhimurium DT104 outlasted the current withdrawal time of 10 days for Baytril (commercial veterinary formulation of enrofloxacin).


CONCLUSIONS
In conclusion, our study has provided direct evidence that enrofloxacin-treated pigs could be entering abattoirs with higher numbers of quinolone-resistant zoonotic bacteria than untreated pigs, increasing the risk of these entering the food chain.
Delsol
Anne A
AA
Division of Farm Animal Science, Department of Clinical Veterinary Science, Langford BS40 5DU, UK. a.a.g.delsol@bris.ac.uk
Woodward
Martin J
MJ
Roe
John M
JM
D000818:Animals; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D002939:Ciprofloxacin / Q000494:pharmacology; D015169:Colony Count, Microbial; D003510:Cyclohexanes / Q000494:pharmacology; D027081:DNA Gyrase / Q000235:genetics; D024881:Drug Resistance, Bacterial; D000077422:Enrofloxacin; D005243:Feces / Q000382:microbiology; D024841:Fluoroquinolones / Q000627:therapeutic use*; D005798:Genes, Bacterial; D008826:Microbial Sensitivity Tests; D009268:Nalidixic Acid / Q000494:pharmacology; D010641:Phenotype; D015363:Quinolones / Q000627:therapeutic use*; D012480:Salmonella Infections / Q000188:drug therapy* / Q000382:microbiology; D019779:Salmonella enterica / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D013552:Swine
D000900:Anti-Bacterial Agents; D003510:Cyclohexanes; D024841:Fluoroquinolones; D015363:Quinolones; D009268:Nalidixic Acid; D000077422:Enrofloxacin; D002939:Ciprofloxacin; D027081:DNA Gyrase