Immunobiological relationships of the enterotoxins produced by cholera toxin gene-positive (CT⁺) and -negative (CT⁻) strains of Vibrio cholerae O1

Abstract

The optimum rabbit ileal loop (RIL) reacting doses of the new cholera toxin (NCT) produced by cholera toxin gene-negative (CT⁻) strain X-392 and of the enterotoxin produced by cholera toxin gene-positive (CT⁺) strain 569B of Vibrio cholerae Ol were found to be 32 µUg and 22 µUg respectively. Production of NCT by the CT⁺ strain, in addition to CT, was confirmed by in-vivo neutralisation tests. Anti-569B-enterotoxin neutralised the optimum RIL reacting activity of NCT completely at 1 in 16 dilution, whereas the activity of 569B enterotoxin was only partially neutralised (44%) by anti-NCT. Similarly, partial neutralisation (66%) was observed when purified anti-CT was mixed with 569B enterotoxin. Therefore, the fluid accumulation produced in the RIL by 569B enterotoxin was the combined effect of both CT and NCT. No antigenic relationship between NCT and CT could be demonstrated in gel-diffusion tests.