Gardnerella vaginalis
General Characteristics Gardnerella vaginalis is a short, pleomorphic gram-positive rod or coccobacillus that often stains gram-variable. Gardnerella vaginalis has a gram-positive type of cell wall; however, the peptidoglycan layer is thinner than that found in other gram positive bacteria, such as Corynebacterium and Lactobacillus. Gardnerella vaginalis is the only species in the genus and was first described in 1953. It is found as normal biota in the human urogenital tract.Gardnerella vaginalis
General Characteristics Gardnerella vaginalis is primarily known for its association with bacterial vaginosis (BV) in humans. For years, G. vaginalis was thought to be the only cause of BV. However, the organism can be isolated from 40% of women without BV. BV is characterized by a malodorous discharge and vaginal pH greater than 4.5. BV generally results from a reduction in the Lactobacillus population in the vagina, followed by an increase in vaginal pH; This results in overgrowth by G. vaginalis and other BV-associated organisms. G. vaginalis can also play a role in UTIs in men and women.Gardnerella vaginalis
distinguishing features: Gram-variable rod; has Gram-positive cell envelope Facultative anaerobe Catalase-negative and oxidase-negative Reservoir: human vagina Transmission: endogenous (normal flora gets disturbed, increased pH)Gardnerella vaginalis
Pathogenesis Polymicrobial infections Works synergistically with other normal flora organisms including Lactobacillus, Mobiluncus, Bacteroides, Peptostreptococcus Thought to flourish when the vaginal pH increases, reduction of vaginal Lactobacillus Follows menses or antibiotic therapy Disease: bacterial vaginosis (vaginal odor, increased discharge (thin, gray, adherent fluid)Gardnerella vaginalis
Laboratory Diagnosis:Microscopy. G. vaginalis often appears as a pleomorphic, gram-variable coccobacillus or short rod. The cells often stain gram-negative. In addition, they can be visualized in wet mounts of vaginal fluid when BV is suspected.The observation of “clue cells,” large squamous epithelial cells with gram-positive and gram-variable bacilli and coccobacilli clustered on the edges, aids the diagnosis of BV, particularly if Lactobacillus rods are absent in the wet mount.Gardnerella vaginalis
Diagnosis: pH >4.5, clue cells (epithelial cells covered with bacteria) on vaginal saline smear; for Whiff test, add KOH to sample and assess for “fishy” amine odor.Culture Characteristics:Vaginal discharge collected from suspected BV cases is the most common specimen used for the isolation of G. vaginalis.Because it is part of the urogenital microbiota, the organism can also be isolated from urine.
Gardnerella vaginalis
Diagnosis: It often takes longer than 24 hours to develop visible colonies, and G. vaginalis grows best in 5% to 7% CO2 at a temperature of 35° C to 37° C.The medium of choice for G. vaginalis is human blood bilayer Tween (HBT) agar.When cultured on human blood, colonies are β-hemolytic, small, gray, and opaque.Treatment:Metronidazole or ClindamycinGardnerella vaginalis
A, Predominance of lactobacilli in Gram stain from healthy vagina. B, Absence of lactobacilli and presence of Gardnerella vaginalis (A arrows) and Mobiluncus spp. (B arrows) morphologies.Gardnerella vaginalis
Gram negative bacilli, nonmotile, pleomorphicShows metachromic granules
Beta-hemolyis on Blood agar
Bacterial vaginosis
Vaginal pH > 4.5
Foul smelling vaginal discharge
Presence of “clue cells” Associated with Mobiluncus
Treatment: Metronidazole
Vaginal smears
Gram: Curved rods (Mobiluncus sp). seen among squamous epithelium.
Papanicolaou: Short Gram-negative rods clusterd onto squamous epithelium to form "clue cells", Doederlein bacilli are never seen.
Papanicolaou: Doederlein bacilli (Lactobacillus) Normal flora vaginal flora.