Two Mannose-resistant Haemagglutinins on Enterotoxigenic Escherichia coli of Serotype O6:K15:H16 or H- Isolated from Travellers' and Infantile Diarrhoea

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Abstract
Enterotoxigenic E. coli of serotype O6:K15:H16 or H- were shown to cause mannose-resistant hemagglutinination [MRHA] of bovine erythrocytes (MHRAbov), a characteristic associated with possession of so-called colonization factor antigen (CFA/II) which facilitates adhesion to the intestinal mucosa. Using putative anti-CFA/II antisera, raised to whole cell vaccines of .**GRAPHIC**. prototype strains of different biotypes with subsequent absorption with their .**GRAPHIC**. variants, 3 immunologically distinct coli surface-associated [CS] antigens were identified on enterotoxigenic strains of this serotype. CS1 antigen was found only on .**GRAPHIC**. isolates of biotype A (rhamnose-negative). Specific anti-CS1 serum agglutinated rhamnose-negative strains, gave a single immunoprecipitate in double immunodiffusion against cell surface extracts of these bacteria and inhibited MRHAbov activity of only biotype A strains. The presence of CS1 serologically correlated with the presence of a 16.3 kilodalton [kDal] polypeptide band sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of extracts. CS2 antigen was identified on .**GRAPHIC**. strains of biotypes B, C and F (rhamnose-positive). Specific anti-CS2 serum agglutinated only the latter strains, gave a single immunoprecipitate against cell surface extracts of only rhamnose fermenting strains, and inhibited MRHAbov activity of only 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. 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 antibodies did not agglutinate nor did they possess hemagglutination inhibition activity. CS3 antigen was also found on an enterotoxigenic isolate series of serotype O8:K40:H9, which was .**GRAPHIC**. and lacked the CS1 and CS2 antigens. A number of CS2-only O-serogroup 6 strains were identified. Expression of MRHAbov activity and the production of CS1, CS2 and CS3 antigens were phenotypically suppressed by growth at 18.degree. C. Loss of heat-stable enterotoxin and also, in most instances of heat-labile enterotoxin production accompanied loss of MRHAbov activity and loss of production of the CS1, CS2 and CS3 antigens. Thus, the findings demonstrate the presence of 2 serologically distinct, biotype-associated hemagglutinins with different MW properties on .**GRAPHIC**. enterotoxigenic E. coli of serotype O6:K15:H16 or H- of human origin of a 3rd non-hemagglutinating surface-associated antigen common to most strains which may also facilitate adhesion.