Identification of Gardnerella (Haemophilus) vaginalis

Different tests for the identification of Gardnerella (Haemophilus) vaginalis and for its differentiation from catalase-negative unclassified coryneforms from the vagina were evaluated on over 200 bacterial strains, with special emphasis on optimal test conditions. A presumptive identification of G. vaginalis in the clinical laboratory can be made on the basis of colonial morphology, clear beta-hemolysis with diffuse edges on human blood bilayer-Tween agar, a negative catalase test, and typical cell morphology in the Gram stain. This procedure will correctly identify 90 to 98% of suspect colonies of G. vaginalis with human blood bilayer-Tween agar as primary isolation medium. Useful additional reactions for the confirmation of G. vaginalis include positive hippurate and starch hydrolysis, positive alpha-glucosidase but negative beta-glucosidase tests, the production of acid from glucose and maltose but not from mannitol, and susceptibility to disks containing metronidazole, nitrofurantoin, sulfonamides, and bile.