Gardnerella vaginalis is a gram-variable rod or coccobacillus. It is a venereally transmitted bacterium that causes bacterial vaginosis⁶. This is a condition characterized by an increase in the numbers of G. vaginalis and various obligate anaerobes, and a concomitant decrease in lactobacilli observed on gram-stained smears. HBT Bilayer Medium, formulated by Totten et al., consists of a bottom layer of Columbia colistin nalidixic acid agar supplemented with peptone, amphotericin B, and polysorbate 80 together with a top layer of the same media with 5% human blood added⁷. It shows significantly higher isolation rates of G. vaginalis than those obtained with other media.

Use HBT BiLayer Medium for selective and presumptive identification of Gardnerella vaginalis.

• Ready to use – Convenience of prepared media
• Selective medium - Colistin, nalidixic acid, and amphotericin B are selective agents that inhibit most gram-negative rods, yeast, and diphtheroids
• Easy to interpret - G. vaginalis produces small, opaque colonies surrounded by a diffuse zone of beta-hemolysis

The casein and meat peptones supply nutrients. Phosphate buffer maintains pH and cornstarch neutralizes toxic fatty acids. Polysorbate 80 enhances the diffusion of beta-hemolysis. The top layer contains the same medium with addition of 5% human blood. Since the zones of beta-hemolysis are viewed through a shallow layer of blood-containing medium, hemolysis is more distinct and easier to detect than with a single layer medium.