Resistance of Gardnerella vaginalis to bactericidal activity of human serum

To assess the sensitivity of Gardnerella vaginalis to the complement mediated bactericidal activity of serum, six laboratory strains were incubated with normal human serum and two strains freshly isolated from women with non-specific vaginitis (NSV) were each incubated with homologous patient serum. There was no significant difference between the number of organisms recovered from unheated or heat inactivated serum after incubation at 37 degrees C for one hour with any of the strains tested. A suspension of G vaginalis incubated at 37 degrees C for one hour in heat inactivated homologous mouse antiserum with unheated normal human serum as a source of complement did not show any less viability than the control mixture using heat inactivated human serum. In contrast, a serum resistant strain of Neisseria gonorrhoeae incubated in heat inactivated homologous mouse antiserum with unheated normal human serum showed noticeably less viability than the control. G vaginalis therefore seems to be resistant to the bactericidal activity of both normal and immune serum.