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

Abstract

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.