Several reports have described @entity5125 strains which were nonpathogenic or weakly pathogenic, but little is known about these low-virulence strains. We found that 9 field @entity5125 strains were hypovirulent and 17 were avirulent, based on the number of @entity19 contaminated and the colonization of their spleens after subcutaneous inoculation. All these strains possessed the known virulence genes. We have now assessed the low virulence of these strains in other assays before determining how they differ from virulent strains. We have shown that the low-virulence strains exhibited a phenotypic stability and were not a mixture of virulent and avirulent bacteria. They did not recover virulence after many passages in @entity19 and colonized the spleens of @entity19 more poorly than virulent strains after i.v. inoculation. Their lethal capacities, determined by 50% lethal dose (LD(50)), were lower than those of virulent strains. Like @entity16085 , 14 of 17 avirulent strains had no LD(50) and were eliminated by the lymph nodes after subcutaneous inoculation. The virulent, hypovirulent, and avirulent strains were always significantly different, whatever the tests of virulence used, confirming the importance of these low-virulence field strains in identifying the proteins involved in virulence.

Experimental validation of low virulence in field strains of XXXX .

@entity19 :: ('10090', 'Species') :: ['mice'] @entity5125 :: ('1639', 'Species') :: ['Listeria monocytogenes', 'L. monocytogenes'] @entity16085 :: ('1642', 'Species') :: ['Listeria innocua']
@entity5125 :: (1639,Species) :: ['Listeria monocytogenes']
