Summary: Enterotoxigenic Escherichia coli of serotype O6:K15:H16 or H– have been shown to cause MRHA of bovine erythrocytes (MRHA), a characteristic associated with possession of so-called CFA (CFA/II) which facilitates adhesion to the intestinal mucosa. Using putative anti-CFA/II antisera, raised to whole cell vaccines of MRHA prototype strains of different biotypes with subsequent absorption with their MRHA variants, three immunologically distinct CS antigens were identified on enterotoxigenic strains of this serotype. CS1 antigen was found only on MRHA isolates of biotype A (rhamnose-negative). Specific anti-CS1 antigen serum agglutinated rhamnose-negative strains, gave a single immunoprecipitate in double immunodiffusion against cell surface extracts of these bacteria, and only inhibited the MRHA activity of biotype A strains. The presence of CS1 serologically correlated with the presence of a 16.3 kDal polypeptide band upon SDS-PAGE of extracts. CS2 antigen was identified on MRHA strains of biotypes B, C and F (rhamnose-positive). Specific anti-CS2 antigen serum agglutinated only the latter strains, gave a single immunoprecipitate against cell surface extracts of only rhamnose fermenting strains, and only inhibited MRHA activity of strains of these biotypes. The presence of CS2 antigen serologically was associated with the presence of a 15.3 kDal polypeptide band in SDS-PAGE patterns of extracts. The CS3 antigen was identified by immunodiffusion tests with extracts of most O6:K15:H16 or H– strains possessing CS1 or CS2 antigen, i.e. independently of biotype, and was associated with the presence of a 14.8 kDal polypeptide band by SDS-PAGE. Anti-CS3 antigen antibodies did not agglutinate nor did they possess haemagglutination inhibition activity. CS3 antigen was also found on an enterotoxigenic isolate series of serotype O8:K40:H9, which was MRHA , and lacked the CS1 and CS2 antigens. A number of CS2-only O-serogroup 6 strains were identified. Expression of MRHA activity and the production of CS1, CS2 and CS3 antigens were phenotypically suppressed by growth at 18°C. Loss of ST and also, in most instances, of LT production accompanied loss of MRHA activity and loss of production of the CS1, CS2 and CS3 antigens. Thus, the findings demonstrate the presence of two serologically distinct, biotype-associated haemagglutinins with different molecular weight properties on MRHA enterotoxigenic of serotype O6:K15:H16 or H– of human origin and of a third non-haemagglutinating surface-associated antigen common to most strains which may also facilitate adhesion.


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