INFLUENCE OF ANIMAL PASSAGE ON HEMOLYSIN AND ENTEROTOXIN PRODUCTION IN VIBRIO-CHOLERAE-01 BIOTYPE EL-TOR STRAINS

Of 43 strains of Vibrio cholerae O1 biotype El Tor isolated over a spa n of almost three decades (1964-1990) from stools of children and adul ts with diarrhoea (25 isolates) and from sewage (three) and water from the river Ganges (15) examined for production of haemolysin and its c orrelation with enterotoxin production, 17 isolates showed haemolysis. The majority of isolates (26), including 68 % of diarrhoeal and 50 % of environmental origin, were non-haemolytic. The titre of haemolysin produced was 4-16 HU/ml, irrespective of the source of isolation. Haem olytic strains caused significantly more fluid accumulation than the n on-haemolytic strains in the rabbit ileal loop (RIL) test. Twenty nine (67.4) V. cholelae biotype El Tor isolates-all the haemolytic and mos t (61.5 %) of the non-haemolytic isolates tested-caused fluid accumula tion. The remaining non-haemolytic strains that caused little or no ac cumulation of fluid did so after one to four consecutive passage(s) th rough RIL without change in haemolytic character; these strains requir ed more consecutive passage through rabbit gut to show haemolysis. All these strains reverted to their original non-haemolytic character on repeated subculture or on storage in the laboratory but continued to s how enterotoxic activity. The present study indicated that El Tor haem olysin is not responsible for fluid accumulation in rabbit gut.