Long-term persistence of multi-drug-resistant Salmonella enterica serovar Newport in two dairy herds.
OBJECTIVE
To evaluate the association between maintaining joint hospital and maternity pens and persistence of multi-drug-resistant (MDR) Salmonella enterica serovar Newport on 2 dairy farms.


METHODS
Observational study.


METHODS
Feces and environmental samples from 2 dairy herds.


METHODS
Herds were monitored for fecal shedding of S enterica Newport after outbreaks of clinical disease. Fecal and environmental samples were collected approximately monthly from pens housing sick cows and calving cows and from pens containing lactating cows. Cattle shedding the organism were tested serially on subsequent visits to determine carrier status. One farm was resampled after initiation of interventional procedures, including separation of hospital and maternity pens. Isolates were characterized via serotyping, determination of antimicrobial resistance phenotype, detection of the CMY-2 gene, and DNA fingerprinting.


RESULTS
The prevalence (32.4% and 33.3% on farms A and B, respectively) of isolating Salmonella from samples from joint hospital-maternity pens was significantly higher than the prevalence in samples from pens housing preparturient cows (0.8%, both farms) and postparturient cows on Farm B (8.8%). Multi-drug-resistant Salmonella Newport was isolated in high numbers from bedding material, feed refusals, lagoon slurry, and milk filters. One cow excreted the organism for 190 days. Interventional procedures yielded significant reductions in the prevalences of isolating the organism from fecal and environmental samples. Most isolates were of the C2 serogroup and were resistant to third-generation cephalosporins.


CONCLUSIONS
Management practices may be effective at reducing the persistence of MDR Salmonella spp in dairy herds, thus mitigating animal and public health risk.
Field Disease Investigation Unit, College of Veterinary Medicine, Washington State University, Pullman, WA 99163, USA.
Rowland N
RN
Cobbold
Daniel H
DH
Rice
Margaret A
MA
Davis
Thomas E
TE
Besser
Dale D
DD
Hancock
D000818:Animals; D002353:Carrier State / Q000662:veterinary; D002417:Cattle; D002418:Cattle Diseases / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology*; D004196:Disease Outbreaks / Q000662:veterinary; D024901:Drug Resistance, Multiple, Bacterial; D004783:Environmental Microbiology; D005243:Feces / Q000382:microbiology; D005260:Female; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D015995:Prevalence; D012481:Salmonella Infections, Animal / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology; D019779:Salmonella enterica / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification; D012703:Serotyping / Q000662:veterinary; D014861:Washington / Q000453:epidemiology