Fluctuations in Escherichia coli O-serotypes in Pigs Throughout Life in the Presence and Absence of Antibiotic Treatment

A detailed study, throughout life, of the coliform and Escherichia coli gut flora of two pigs, is presented. One pig was given oral tetracycline for 3 d on two separate occasions; the other pig was not treated and housed separately. The fluctuations in numbers of coliforms, O-serotypes of E. coli , the occurrence and persistence of antibiotic resistance, and their interrelations, are analysed for both animals. Oral tetracycline profoundly affected the proportion of antibiotic sensitive and resistant E. coli , and, by selecting for R-factor bearing O-serotypes, limited the number of O-serotypes isolated from individual faceal specimens. Specific O-serotypes exhibited marked differences in their ability to persist in the gut of the control pig. The R-factor bearing O-serotypes, selected by tetracycline treatment, also showed differences in ability to persist after treatment indicating that properties other than the possession of R-factors, decide colonizing ability. The size of the colony sample for serotype analysis is discussed.