Effect of tetracycline on the attachment of K88+ enterotoxigenic Escherichia coli to porcine small-intestinal cells.

The attachment of six strains of K88+, porcine pathogenic, enterotoxigenic Escherichia coli to isolated porcine intestinal mucosal cells was decreased following growth in the presence of concentrations of oxytetracycline below the minimal inhibitory concentration (MIC). The decrease in binding by the wild-type strains was detected at concentrations of drug as low as 0.001 microgram/ml, which was greater than four orders of magnitude below the MIC. When drug resistance was induced in these six strains, there was still a decrease in binding when the bacteria were grown in the presence of tetracycline. This decrease was comparable to the decrease in binding capacity of the wild-type strains caused by growth in the presence of tetracycline. In contrast, when one strain (G1108E) was made tetracycline resistant by the introduction of the R16 plasmid, the antibiotic had less effect on the binding of this strain than on the wild-type strain; however, growth in the presence of antibiotic still decreased adhesion. Overall, oxytetracycline decreased the adhesion of wild-type, induced-resistant, and genetically resistant K88+ enterotoxigenic E. coli to porcine small-intestinal cells, and this effect occurred at antibiotic concentrations several orders of magnitude below the MIC.