CORRELATION BETWEEN PRODUCTION OF LISTERIOLYSIN-O BY VARIANTS OF LISTERIA-MONOCYTOGENES AND THEIR VIRULENCE FOR RABBITS

L. monocytogenes serovar 1/2a NCTC 973 was passaged through rabbits an d the severity of infection at each passage was determined by counting viable bacteria from infested organs and recording the time of death. A comparative evaluation of the levels of hemolysin produced in vitro by the original and six variant cultures (V-1-V-6) was done by determ ination of hemolytic units (CHU). While virulence of the cultures enha nced at each passage (2.2 X 10(9) CFU/g of the spleen for Vg as compar ed to 5.0 X 10(6) CFU/g spleen for the parent culture), the CHU decrea sed considerably, 3 CHU for the V-6 as compared to 40 CHU for the pare nt strain. The results suggest that the level of in vitro production o f listeriolysin may not parallel the pathogenicity of L. monocytogenes for rabbits.