Phenotypic Suppression of "Escherichia coli" K88ac antigen by selective media and termperature variations
The K88ac antigen, thought to he a pilus on "Escherichia coli", has been determined to be one of the virulence factors in neonatal porcine colibacillosis. Using five different "E. coli" strains, the suppression of this antigen was studied on Tergitol-7(T7) and Nutrient Agar (Nut) at 18°C and 35°C. Monospecific K88ac antisera, the guinea pig red blood cell mannose resistant agglutination test, and isolated porcine gut cell adherence test were used to demonstrate the presence or absence of K88ac activity. When tested after various incubation times, the phenotypic suppression was different among strains. When tested for gut cell adherence, the expression of K88ac antigen, did not affect the results, whereas Fx antigen, a new antigen found on certain "E. coli" strains, was directly related to the gut cell adherence reaction. The use of transmission electron microscopy failed to demonstrate any visible morphological changes consistant with the suppression of the K88ac antigen activity. The lack of morphological changes, the relationship of Fx antigen and its effect upon adherence, leads one to speculate that the K88ac may not be a true pilus and that more than one factor is involved in gut cell adherence by these organisms.
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