VIRULENT TO AVIRULENT CONVERSION OF LEGIONNAIRES DISEASE BACTERIUM (LEGIONELLA-PNEUMOPHILA) - ITS EFFECT ON ISOLATION TECHNIQUES

Suspensions of the Legionnaires’ disease bacterium (Legionella pneumophila-, LDB) were prepared from the yolk sacs of infected egg embryos, the spleens of infected guinea pigs, and cultures of the organism propagated on enriched Mueller-Hinton agar. Each suspension was titrated to determine the number of bacterial colonies (cfu), yolk sac 50% lethal doses (ysld50), guinea pig 50% infectious doses (gpid50), and guinea pig 50% lethal doses (gpld50) produced by 1 ml of inoculum. The numbers of cfu/YSLD50, gpid50, and gpld50 were then calculated for each suspension. The suspension from yolk sacs had 1 cfu/YSLD50 and 10 cfu/cpiD50. The suspension from spleens of guinea pigs also had 1 cfu/YSLD50. Organisms propagated on Mueller-Hinton agar, however, had > 107 cfu/YSLD50 and 105 cfu/GPlDgo. Thus, the LDB lost virulence when it was cultivated on agar. Guinea pigs vaccinated either subcutaneously or intraperitoneally with LDB grown on Mueller-Hinton agar resisted challenge with virulent LDB. © 1979 by The University of Chicago.