Summary: strain 334 is a human enterotoxigenic strain of serotype 015:H11 which had previously been shown to produce “attachment pili”. These fimbriae were compared with other colonization factors. From strain 334 a mannose-resistant haemagglutination positive colony 334A and a mannose-resistant haemagglutination negative variant 334C were isolated. By electron microscopy the fimbriae of strain 334A were shown to have a helical structure resembling coli-surface-associated antigen (CS5) fimbriae. An antiserum was raised to strain 334A and absorbed with a fimbriae-negative variant of that strain, 334C. By immuno-electron microscopy this antiserum was shown to coat fimbriae of strain 334A but not CS5 fimbriae produced by strain E17018A. Conversely, CS5 antiserum did not coat the fimbriae produced by strain 334A. No antigenic cross-reaction was detected between these intact fimbriae when anti-strain 334A serum and CS5 antiserum were used in immunodiffusion tests. By enzyme-linked immunosorbent assays (ELISAs) the fimbriae of strain 334A were shown to be antigenically unrelated to most other human ETEC adhesins, namely colonization factor antigens (CFA/I, CFA/III and CFA/IV), coli-surface-associated antigens (CS1, CS2, CS3, CS4, CS6 and CS17) and putative colonization factors (PCF0159:H4 and PCF0166). However, a heated suspension of strain 334A reacted weakly with CS5 antiserum in an ELISA. By SDS-PAGE the fimbriae of strain 334A were shown to consist of subunits of similar size to CS5 subunits, that is about 21·5 kDa. Western immunoblotting revealed that the subunits of 334A and CS5 fimbriae shared common epitopes. Expression of 334A fimbriae was controlled by a plasmid which also coded for enterotoxin production, a system similar to that reported for a number of other human ETEC attachment factors. Strain 334A fimbriae have therefore been designated as CS7 fimbriae. Surveillance with CS7 anti-serum of ETEC with no known attachment factors showed two other strains of serotype O15:H11, one strain of serotype O103:H49 and 20 strains of serotypes O114:H49 and H- to possess CS7 fimbriae.


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