Acquisition and epidemiology of antibiotic-resistant Escherichia coli in a cohort of newborn calves.
OBJECTIVE
The acquisition of antibiotic-resistant commensal Escherichia coli was examined in a cohort of newborn calves.


METHODS
Faecal samples were collected weekly from calves over a 4 month period and screened for E. coli resistant to ampicillin, apramycin and nalidixic acid at concentrations of 16, 8 and 8 mg/L, respectively. E. coli viable counts were performed on samples from a subset of calves.


RESULTS
All calves acquired ampicillin- and nalidixic acid-resistant E. coli, while only 67% acquired apramycin-resistant E. coli during the study. Sixty-seven per cent of samples were resistant to at least one of the three antibiotics. Prevalence of ampicillin and nalidixic acid resistance was high initially and declined significantly with age (P < 0.001). No temporal or age-related pattern was observed in the prevalence of apramycin resistance. Housing the cohort had a significant effect on the prevalence of nalidixic acid resistance (P < 0.001). Total and ampicillin- and nalidixic acid-resistant E. coli counts declined with calf age (P < 0.001), with the rate of decline in ampicillin-resistant counts being greater than that for total counts (P < 0.001). The proportion of total E. coli counts that were resistant to ampicillin or nalidixic acid also declined with age (P < 0.001).


CONCLUSIONS
Cohort calves rapidly acquired antibiotic-resistant bacteria within days of birth. Carriage of resistant bacteria was associated with both age and housing status of the cohort.
Hoyle
Deborah V
DV
Centre for Tropical Veterinary Medicine, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Veterinary Centre, Roslin, Midlothian EH25 9RG.
Knight
Hazel I
HI
Shaw
Darren J
DJ
Hillman
Kevin
K
Pearce
Michael C
MC
Low
J Chris
JC
Gunn
George J
GJ
Woolhouse
Mark E J
ME
D000667:Ampicillin / Q000494:pharmacology; D000668:Ampicillin Resistance / Q000235:genetics; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000494:pharmacology; D002417:Cattle; D015331:Cohort Studies; D015169:Colony Count, Microbial; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology* / Q000662:veterinary*; D005243:Feces / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D009268:Nalidixic Acid / Q000494:pharmacology; D009328:Nebramycin / Q000031:analogs & derivatives* / Q000494:pharmacology; D010406:Penicillins / Q000494:pharmacology; D012606:Scotland / Q000453:epidemiology
D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D010406:Penicillins; D009328:Nebramycin; C011666:apramycin; D009268:Nalidixic Acid; D000667:Ampicillin