Comparison ofculture andmicroscopy inthe diagnosis ofGardnerella vaginalis infection

SUMMARY A comparison was madebetween humanbloodagar containing amphotericin B, nalidixic acidandeither gentamicin orcolistin fortheisolation ofGardnerella vaginalis fromcases ofnon-specific vaginitis seenina clinic forsexually transmitted diseases. Themediumcontaining gentamicin was more inhibitory fornon-Gardnerella species, butnotsufficiently inhibitory toallow direct plating intheclinic without spreading forsingle colonies. Thediffuse betahaemolysis producedbyG vaginalis on human,butnoton horse blood agar,proved veryuseful indifferentiating itfromother vaginal organisms andwas notaffected bytheantibiotics used. Thischaracteristic, together withGramstain morphology, oxidase andcatalase, provides a simple, reliable methodof identifying G vaginalis. Sixty women withsymptomsofvaginitis, inwhom no other pathogen was isolated, were examined byculture andmicroscopy. GardnerelIa vaginalis was grown from45 whereas only31hadpositive microscopy (clue cells orGram-variable bacilli). There was no significantdifference between therateofisolation ofG vaginalis inthegroup withpositive microscopy (25/31) andthatwithnegative microscopy (20/31). Non-specific vaginitis isa common condition characterised byan increased vaginal discharge, often foulsmelling, whichisnotattributable to uterine infection, Trichomonas vaginalis orcandidal infection. Gardnerella vaginalis hasbeenclosely associated withthis condition.1 2Theisolation and identification ofGvaginalis intheroutine laboratory canbebothtime-consuming anddifficult. Diagnosis istherefore mostusually madeonthebasis ofthe foulsmelling discharge, ontheliberation ofamines withafishy odourwhen10%KOH isaddedtoit, andonthecharacteristic microscopical appearance ofthewetpreparation andofGram-stained smears ofthedischarge.1 2Someworkers have, however, foundapoorcorrelation between theisolation ofG vaginalis andthemicroscopical appearance ofthe discharge3 4andanydetailed study oftheaetiology andepidemiology ofthecondition needs a good, preferably simple, cultural basis. Gardnerella vaginalis isaslow-growing organism which, onordinary media, isdifficult todifferentiate fromother vaginal bacteria. Itstaxonomy hasbeen unsatisfactory, having beenpreviously classified bothasa Haemophilus anda Corynebacterium.