SUMMARY. When fimbriate (Fim +) strains of were grown in static broth, many bacteria were in the fimbriate phase and bore fimbrial mannose-sensitive haemagglutinin (MSHA) that enabled them to adhere to guinea-pig and other erythrocytes and to agglutinate them in rocked tile and static settling tests. When either Fim+ or Fim- strains were grown on phosphate-buffered nutrient agar, the bacteria formed a diffusible, mannose-resistant haemagglutinin (MRHA) that gave dispersed sediments with sheep and pig erythrocytes in static settling tests, but without evidence of bacterial adhesion to the erythrocytes. On exposure, from above or from below, to cultured HEp2 and HeLa cells for 30 or 90 min at 37°C, motile MSHA-rich, MRHA-negative broth-grown bacteria adhered to the cells in large numbers (, 20-100/cell), but motile MSHA-negative, MRHA-negative broth-grown bacteria and non-motile MSHA-negative, MRHA-rich agar-grown bacteria adhered in only small numbers (usually > 1/cell). Thus, strong adhesiveness of bacteria for cultured cells appears to depend upon the presence of MSHA, not MRHA, and as Fim- (MSHA-negative) strains of are known to be highly infective in animals, a strong reaction in the in-vitro model does not reflect a property of the bacteria essential for infectivity .


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