Comparison of culture and microscopy in the diagnosis of Gardnerella vaginalis infection.

A comparison was made between human blood agar containing amphotericin B, nalidixic acid and either gentamicin or colistin for the isolation of Gardnerella vaginalis from cases of non-specific vaginitis seen in a clinic for sexually transmitted diseases. The medium containing gentamicin was more inhibitory for non-Gardnerella species, but not sufficiently inhibitory to allow direct plating in the clinic without spreading for single colonies. The diffuse beta haemolysis produced by G vaginalis on human, but not on horse blood agar, proved very useful in differentiating it from other vaginal organisms and was not affected by the antibiotics used. This characteristic, together with Gram stain morphology, oxidase and catalase, provides a simple, reliable methods of identifying G vaginalis. Sixty women with symptoms of vaginitis, in whom no other pathogen was isolated, were examined by culture and microscopy. Gardnerella vaginalis was grown from 45 whereas only 31 had positive microscopy (clue cells or Gram-variable bacilli). There was no significant difference between the rate of isolation of G vaginalis in the group with positive microscopy (25/31) and that with negative microscopy (20/31).