Transferable Drug Resistance in Escherichia coli Isolated from Antibiotic-Fed Chickens

The isolation and transferable drug resistance of Escherichia coli from the feces of chickens after oral administration of tetracylcine, chloramphenicol, rifampicin, and amoxicillin were studied. Each antibiotic was administered at two different dosages to four groups of 12 chickens. Treatment was carried out for 3 weeks. Feces were taken weekly and bacteriological examinations performed. E. coli biotypes were identified by fermentation and enzymatic reaction patterns. Antibiotic sensitivity tests were performed on all E. coli isolates. Rapid appearance of E. coli biotypes showing drug-resistance to each antibiotic was observed as soon as 1 week after treatment. Resistance was not detectable a few days after interruption of antibiotic administration. All E. coli strains showing drug resistance to the antibiotic under examination were studied to observe their capacity to transfer antibiotic resistance to E. coli K 12 E 711 F-strain. A high percentage of resistant E. coli strains transferred their antibiotic resistance to E. coli K 12. Transferable drug resistance was demonstrated mainly in tetracycline resistant E. coli.