The effect of antibiotics on mannose‐resistant haemagglutination by K88‐ and K99‐positive Escherichia coli strains

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Abstract
Five E. coli strains carrying K99 antigen isolated from the intestines of calves which had succumbed to diarrhea and 6 K88-positive strains isolated from fatal cases of diarrhea in piglets were examined for mannose-resistant hemagglutination (MRHA) capacity against pig erythrocytes. The bovine strains showed a geometric mean MRHA titer of 1/18 and the porcine strains one of 1/45. Similar experiments were carried out after addition of the following antibiotics in doubling dilutions: ampicillin, chloramphenicol, colistin, dihydrostreptomycin, gentamicin, neomycin, polymyxin B and oxytetracycline. Colistin and polymyxin B had a marked concentration-dependent inhibitory effect on MRHA. Neomycin and gentamicin also inhibited MRHA, but to a lesser degree. Chloramphenicol, dihydrostreptomycin and oxytetracycline showed no effect. With ampicillin, the ratios were inversely proportional to the concentration. Evidently, this antibiotic has an enhancing effect on the hemagglutination.

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