The identification of Gardnerella vaginalis

A collection of 72 strains of catalase-negative gram-positive, -negative and -variable cocco-bacilli isolated from samples of vaginal discharge from women with non-specific vaginal infection was examined in an attempt to develop an identification system for Gardnerella vaginalis that could be used in a diagnostic laboratory. Carbohydrate fermentation tests were found to be poorly reproducible and of little differentiating value. Enzyme tests were found similarly unhelpful, as were many antibiotic-susceptibility and chemical-inhibition tests. However, seven tests--susceptibility to trimethoprim and two concentrations of metronidazole, growth in the presence of 2% (w/v) sodium chloride and on nutrient agar, lactic acid production from glucose and beta-haemolysis on human-blood agar--were used successfully in this study to separate G. vaginalis from catalase-negative coryneforms and lactobacilli. Of these tests, susceptibility to trimethoprim and metronidazole together with beta-haemolysis on human blood agar are the most likely to provide a rapid, accurate identification. A possible identification scheme is outlined.