Antibiotic resistance in gut bacteria from dairy calves: a dose response to the level of antibiotics fed in milk.
Dairy calves are commonly fed milk from cows treated with antibiotics. The concentration of beta-lactam antibiotic residues found in milk from treated cows was used to determine the range of concentrations of penicillin used in a dose-regulated experiment. Thirty-one Holstein calves were randomly assigned to milk with penicillin G added at concentrations of 0, 6.25, 12.5, 25, and 50 microl/kg. Fecal swabs were taken from each calf twice weekly. Resistance to penicillin was tested by measuring the zone of inhibition in bacterial growth around a disk impregnated with the antibiotic. Inhibition was greatest for bacteria from calves fed milk with no penicillin (2.89 +/- 0.14 mm), and declined as the penicillin dose provided in the milk increased (to a low of 0.70 +/- 0.10 for the 50 microl/kg treatment group). In conclusion, resistance of gut bacteria to antibiotics increases with increasing concentrations of penicillin in the milk fed to dairy calves.
Langford
F M
FM
Department of Veterinary Clinical Studies, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Veterinary Centre, Easter Bush, Midlothian, EH25 9RG, UK.
Weary
D M
DM
Fisher
L
L
D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage*; D001419:Bacteria / Q000187:drug effects*; D002417:Cattle; D004032:Diet; D004305:Dose-Response Relationship, Drug; D004352:Drug Resistance, Microbial; D007422:Intestines / Q000382:microbiology*; D008892:Milk / Q000737:chemistry; D010403:Penicillin Resistance; D010406:Penicillins / Q000032:analysis
D000900:Anti-Bacterial Agents; D010406:Penicillins