Postweaning diarrhea in swine: effects of oxytetracycline on enterotoxigenic Escherichia coli infection

Investigators have found that oxytetracycline decreases the adhesion of K88+ Escherichia coli to intestinal epithelial cells in vitro. This occurs with oxytetracycline-sensitive E coli at drug concentrations less than those required to prevent growth and with E coli that are resistant to the drug. We conducted experiments to determine whether oxytetracycline alters the disease caused by an oxytetracycline-resistant K88+ enterotoxigenic strain of E coli. Oxytetracycline-treated pigs (inoculated with K88+ E coli) did not differ from nontreated pigs in the incidence or severity of diarrhea, nor in the shedding of K88+ E coli. However, during recovery, weight gain by treated pigs was slower than that of nontreated pigs. The control pigs were not inoculated with E coli, and they remained clinically normal. Oxytetracycline-treated controls gained weight faster than nontreated controls. Some controls were genetically resistant to K88+ E coli, others were susceptible. The K88-resistant oxytetracycline-treated controls gained weight faster than the K88-susceptible oxytetracycline-treated and non-treated controls.