MOLECULAR CHARACTERIZATION OF ENTEROTOXIGENIC ESCHERICHIA-COLI (ETEC)ISOLATED IN NEW-CALEDONIA (VALUE OF POTENTIAL PROTECTIVE ANTIGENS IN ORAL VACCINE CANDIDATES)

The role of enterotoxigenic Escherichia coli (ETEC) in childhood diarr hoea in New Caledonia was demonstrated in previous epidemiological wor ks. This study was undertaken in order to characterize these strains a nd to determine whether bacterial components of current vaccine candid ates (toxin. colonization factor antigens, O:H antigens) would be usef ul in our region. A total of 24 ETEC strains were studied: 5 strains p roduced heat-labile enterotoxin. 17 strains produced heat-stable enter otoxin (9 STp and 8 STh), and 2 strains produced both toxins (1 LT/STp /STh and 1 LT/STh). E. coli strains were screened for the presence of genes encoding for enterotoxins (DNA dot blot and Southern hybridizati on assays); results obtained with probes were closely correlated and w ere in agreement with biological assays. No two ETEC strains possessed similar plasmid profiles, and DNA sequences encoding for enterotoxins were located on plasmids ranging from 58 to 75 MDa. The O:H (01:H-,02 :H7, 06:H16, 025:H-, 027:H7, 028ab:H9, 052:H10, 064:H5, 070:H-, 078:H1 2, 088:H25, 099:H6, 0101:H-, 0126:H12, 0166:H30) serotypes are present ed (all the strains were typable, but some ETEC serotypes were unusual ). By using antisera against colonization factor antigens (CFA) I and It, results showed that 9 of the 24 ETEC strains expressed CFA (2 CFA/ II and 7 CFA/I). These strains possessed high bacterial surface hydrop hobicity. Fifteen ETEC did not possess CFA; among these, 11 did not ex hibit high hydrophobicity or show haemagglutination activity. Four of the 15 CFA-negative strains exhibited high hydrophobicity (two 064:H45 . one 070:H- and one 088:H25) but no haemagglutination in the presence or absence of mannose. Only 7 of 24 ETEC expressed resistance to ampi cillin, trimethoprimsulphamethoxazole or tetracycline. Data indicate t hat several ETEC isolates would be refractory to current Vaccine candi dates, and that for vaccine to be effective in our region, other antig ens must be included.