IMMUNIZATION AGAINST THE COLONIZATION FACTOR ANTIGEN-I OF ENTEROTOXIGENIC ESCHERICHIA-COLI BY ADMINISTRATION OF A BIVALENT SALMONELLA-TYPHIMURIUM AROA STRAIN

An expression plasmid (pCFA-1) carrying the cfaB gene that codes for t he enterotoxigenic Escherichia coli (ETEC) fimbrial adhesin colonizati on factor antigen I (CFA/I) subunit was constructed and used to transf orm a derivative of the attenuated Salmonella typhimurium aroA vaccine strain SL3261 carrying an F'lacI(q). Treatment of the transformed str ain with isopropyl-beta-D-thiogalactopyranoside (IPTG) resulted in ele vated in vitro expression of the CFA/I subunit. Although flagellar fun ction and lipopolysaccharide (LPS) synthesis were similar in both the parental and the recombinant strains, spleen colonization was reduced in the recombinant strain. All BALB/c mice parenterally inoculated wit h the recombinant strain developed significant antiCFA/I and anti-LPS serum antibody titers (P<0.05). Moreover, 2 of 5 mice orally inoculate d with the engineered Salmonella strain developed anti-CFA/I intestina l IgA (P>0.05) while 4/5 of the same mice developed anti-LPS IgA (P<0. 05). The results indicate that the vaccine strain elicited an antibody response against the bacterial host both after oral and intravenous i mmunization while the response against the CFA/I antigen was significa nt only after inoculation by the intravenous route.