Minimal criteria for the identification of Gardnerella vaginalis isolated from the vagina.

Vaginal swabs were examined for the presence of Gardnerella vaginalis. Of 294 isolates with appropriate colonial and cellular morphology subjected to an identification procedure, 203 (69%) were identified as G vaginalis. The 91 isolates not identified as G vaginalis were differentiated by their inability to ferment starch, cause diffuse beta haemolysis on human blood agar or hydrolyse hippurate. Other tests, often used in the identification of G vaginalis, were found to be insufficiently specific. Failure to ferment starch coexisted with failure to cause beta haemolysis and/or hydrolyse hippurate. The starch fermentation test may therefore be omitted. The tests for beta haemolysis and hippurate hydrolysis, being relatively simple to perform and interpret, are considered indispensable for the accurate identification of G vaginalis in the service laboratory.