Response of wild-type mutants of Vibrio cholerae O1 possessing different combinations of virulence genes in the ligated rabbit ileal loop and in Ussing chambers: evidence for the presence of additional secretogen

Five wild-type mutant strains of Vibrio cholerae serogroup O1 that lacked t he CTX virulence cassette, or contained a natural deletion of a virulence g ene within the CTX virulence cassette, or possessed an additional virulence gene, along with a prototype toxigenic strain representing the Fl Tor clas sical biotypes were examined by in-vivo and in-vitro methods to determine t heir enterotoxic potential. The ability of whole cells and culture supernat es of the strains to cause fluid accumulation in the rabbit ileal loop mode l revealed a pattern consistent with the presence of the various virulence gene(s), with those possessing the intact CTX virulence cassette being the most secretogenic, Culture supernates of strains without the CTX virulence cassette or the strain with an incomplete cassette were also able to evoke mild to moderate fluid accumulation in the rabbit ileal loop, Of the variou s media used, AKI and brain heart infusion broth appeared to support the pr oduction of a hitherto unknown secretogenic factor, because culture superna tes of the non-toxigenic V. cholerae O1 strains showed higher fluid accumul ation ratios when grown in these media than in the others. To confirm that the fluid accumulation elicited by these strains in the ileal loop was due to enterotoxin activity, the effect of supernate of the strains was examine d in rabbit small intestine mounted on Ussing chambers. Increases in short circuit current and tissue conductance, as compared with the medium control , were observed even with the strains that did not possess the CTX virulenc e cassette, confirming their ability to disrupt the function of intestinal tissue. From these studies, it was concluded that strains of V. cholerae O1 devoid of the CTX virulence cassette were still able to elicit a secretory response in the ileal loop and displayed enterotoxic activity in an in-vit ro experimental model.