Enterotoxigenic (ETEC) strains of nineteen serogroups which produced colonization factors (coli-surface-associated antigens CS5, CS6, CS7 and CS17, colonization factor antigen CFA/III and putative colonization factors PCFO159:H4, PCFO166 and PCFO9) were tested for hybridization with a DNA probe containing the sequence that regulates expression of CFA/I. Strong colony hybridization, similar to that with the CFA/I-positive control strain H10407, occurred with ETEC strains of serogroups O27, O159 and O169 which produced CS6 antigen, and with all the strains which produced PCFO166 fimbriae. Weak colony hybridization, compared to the control strain, was found with ETEC producing CS5 fimbriae with CS6 antigen, CFA/III fimbriae with CS6 antigen, CS7 fimbriae or PCFO159:H4 fimbriae. CS6-antigen-positive strains of serogroups O79, O89 and O148 and all the CS17-antigen-positive and PCFO9-fimbriae-positive strains were negative in colony hybridization tests with the probe. Plasmid DNA of nine ETEC strains and their colonization-factor-negative derivatives was tested for hybridization with the probe and with ST and LT oligonucleotide probes. The sequences that hybridized with the probe were on the plasmids which coded for enterotoxin production. Fifteen strains were transformed with NTP513, a recombinant plasmid which contains the CFA/I region 1 fimbrial subunit operon but lacks a functional sequence, in order to determine whether DNA in any of these strains could substitute for the sequence in the regulation of production of CFA/I fimbriae. Transformants of five strains which produced the colonization factors CS6, PCFO166, CS5 + CS6, CS7 and PCFO9, and of one strain which was a colonization-factor-negative derivative of the CS5,CS6-producing strain E17018, gave good production of CFA/I fimbriae comparable to the CFA/I-positive control strain H10407. Transformants of two strains, producing PCFO159 fimbriae and CS17 antigen, respectively, gave weak CFA/I production. Transformants of one strain producing CS6 antigen and of six colonization-factor-negative derivatives did not produce CFA/I fimbriae. These results showed that plasmids in seven of eight types of colonization-factor-positive strains contained gene sequences which could substitute functionally for the sequence. Only two of these strains had gene sequences that hybridized strongly with the probe.


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