Gardnerella vaginalis - Classification, Clinical Manifestation, Lab Diagnosis, AST

Classification of Gardnerella vaginalis

Gardnerella vaginalis can be classified as:

Domain: Bacteria

Phylum: Actinomycetota

Class: Actinomycetia

Order: Bifidobacteriales

Family: Bifidobacteriaceae

Genus: Gardnerella

Species: vaginalis

Introduction to Gardnerella vaginalis

Gardnerella vaginalis is small, facultatively anaerobic, pleomorphic, gram-negative rods (sometimes gram-variable rods), non-capsulated, non-motile, non-sporing microorganisms. They are present as a commensal in the male urethra and vagina.

Gardnerella vaginalis causes non-specific vaginitis, bacterial vaginosis, and cervicitis in association with anaerobic vaginosis. The condition is characterized by foul-smelling vaginal discharge with a fishy odor and acidic pH.

Clinical Manifestation of Gardnerella vaginalis

Gardnerella vaginalis, along with numerous microflora, is associated with clinical manifestations such as bacterial vaginosis. The infection may manifest as irregular vaginal discharge (gray or yellow-green in color), vaginal irritation (pruritus), fish-like odor, or may even remain asymptomatic.

The condition occurs after the Lactobacillus population, which is responsible for the acidic environment, is overcome by other anaerobic microflora. The change in vaginal pH triggers the infection.

Infections caused by Gardnerella vaginalis can be differentiated from infections caused by Trichomonas and Candida albicans by the use of the amine whiff test. All show similar symptoms but require different treatments.

Lab diagnosis of Gardnerella vaginalis

The laboratory diagnosis of Gardnerella vaginalis begins with the collection of samples/specimens.

Sample

• vaginal swab, vaginal discharge, endocervical swab

• blood

• urine

• pharynx

Microscopy

• gram staining and microscopy of the smear shows Gram-variable small bacilli and the presence of clue cells. These clue cells are the vaginal epithelial cells covered with many small gram-variable rods, which can be Gardnerella vaginalis.

Culture

The culture of Gardnerella vaginalis can be done by following steps:

• inoculated on (BA) Human blood polysorbate so medium which contains colistin, nalidixic acid, and amphotericin D that makes it selective for Gardnerella vaginalis

• incubated at 5% CO2 at 33-37°C for 48 hours

• the colonies are small, opaque colonies with distinct β-hemolysis

• Identification by Gram staining, coagulase-negative, and positive hippurate hydrolysis test

Confirmatory identification

The confirmatory identification of Gardnerella vaginalis includes:

• gram stain => gram variable cocco-bacilli

• diffuse β-hemolysis

• Catalase negative, Oxidase negative

• Fructose, Galactose, Glucose, Mannose, and ribose fermenter

• Zone of Inhibition (ZOI) in AST =>Meteronidiazole (50 micrograms)

  Trimethoprim and sulphamide

Other tests

To differentiate the infection of Gardnerella vaginalis, from Trichomonas and Candida albicans, numerous tests are used including the amine whiff test. In this test, 10% KOH is added to the discharge. If the fishy smell is produced, then the etiological agent is Gardnerella vaginalis.

AST of Gardnerella vaginalis

Gardnerella vaginalis also tested for antibiotic sensitivity.

• sensitive to penicillin, ampicillin, and trimethoprim

• resistant to gentamicin, nalidix acid and colistin

• Metronidazole, Clindamycin is the drug of choice - can be administered orally or as vaginal gel/cream