Gardnerella vaginalis: Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes


Gardnerella vaginalis is a Gram-variable bacterium that is considered to be a facultative anaerobe, meaning it can survive in both aerobic and anaerobic environments. It is the main causative agent of bacterial vaginosis (BV), a common vaginal infection in women of reproductive age. BV is characterized by a disruption in the normal balance of bacteria in the vagina, leading to an overgrowth of certain harmful bacteria like G. vaginalis.

It was first identified by Gardner and Dukes in 1955, and it was initially classified as Haemophilus vaginalis. However, later studies revealed its unique characteristics, and it was reclassified as Gardnerella vaginalis in honor of the scientist who discovered it.

The bacterium is typically found in the vaginal flora of many women, but it becomes problematic when it multiplies excessively and outnumbers the beneficial lactobacilli that normally dominate the vaginal environment. BV is not considered a sexually transmitted infection (STI) as it can occur in women who are sexually inactive, but it can be associated with sexual activity.

The exact mechanisms by which Gardnerella vaginalis causes BV are not fully understood. However, it is believed that the overgrowth of this bacterium and other anaerobic bacteria leads to the production of substances that disrupt the natural acidity of the vagina, allowing harmful bacteria to thrive.

Symptoms of bacterial vaginosis can include abnormal vaginal discharge that is often grayish-white in color, a fishy odor, and sometimes itching or irritation. However, some women with BV may experience no symptoms at all. If left untreated, BV may increase the risk of certain complications, such as pelvic inflammatory disease (PID) and an increased susceptibility to sexually transmitted infections.

BV is usually diagnosed through clinical evaluation, examination of vaginal discharge, and laboratory tests. Treatment typically involves antibiotic therapy, including metronidazole or clindamycin, to help restore the normal vaginal flora and alleviate the symptoms.


Gardnerella vaginalis is a small, pleomorphic bacterium with a characteristic morphology. Here are the key features of its morphology:

  1. Shape: G.vaginalis is typically described as a Gram-variable bacterium, meaning it may appear Gram-positive or Gram-negative, depending on the staining method used. This variable staining is due to its unique cell wall composition.
  2. Cell Size: The individual cells of Gardnerella vaginalis are small and typically range from 0.5 to 1.5 micrometers in diameter.
  3. Arrangement: The bacterium is primarily found as single cells, but it can also form short chains or clusters.
  4. Pleomorphism: One of the distinguishing features of G. vaginalis is its pleomorphic nature. Pleomorphism refers to the ability of the bacterium to change its shape and size. It can appear as cocci (round), rod-like, or elongated forms. This pleomorphism can make its identification challenging in clinical settings.
  5. Lack of Capsule and Flagella: It lacks a capsule (a protective layer around the cell) and flagella (whip-like structures used for movement).
  6. Absence of Spores: It is a non-spore-forming bacterium, which means it does not produce spores as a survival mechanism.

Given its small size and pleomorphic nature, G. vaginalis can be quite challenging to identify using conventional microscopy alone. Therefore, in clinical settings, its detection and diagnosis often involve specific laboratory tests, such as Gram staining, culture on selective media, and molecular methods like polymerase chain reaction (PCR) or DNA sequencing.


The pathogenicity of Gardnerella vaginalis is primarily associated with its role in causing bacterial vaginosis (BV). BV is a common vaginal infection characterized by an imbalance in the vaginal microbiota, leading to an overgrowth of certain harmful bacteria, including G. vaginalis, along with other anaerobic bacteria.

The exact mechanisms by which Gardnerella vaginalis contributes to the development of BV are not fully understood, but several factors are believed to be involved:

  1. Biofilm Formation: It has the ability to form biofilms, which are structured communities of bacteria adhering to a surface. Biofilms allow the bacteria to adhere to the vaginal epithelium and resist the body’s immune response and antimicrobial treatments, contributing to the persistence of the infection.
  2. Metabolism and pH: G. vaginalis produces enzymes that break down vaginal mucins, leading to the release of sialidase and other metabolites. These enzymes alter the vaginal pH, making it less acidic, which creates a more favorable environment for the growth of anaerobic bacteria like Gardnerella vaginalis.
  3. Disruption of Vaginal Flora: BV is characterized by a reduction in beneficial lactobacilli, which normally dominate the vaginal environment and help maintain an acidic pH. The overgrowth of Gardnerella vaginalis and other anaerobic bacteria disturbs this delicate balance, leading to the displacement of the lactobacilli and creating an environment conducive to the growth of harmful bacteria.
  4. Production of Toxic Substances: It produces substances such as biogenic amines, including putrescine and cadaverine, which are responsible for the characteristic fishy odor associated with BV.
  5. Immune Response: BV caused by Gardnerella vaginalis can trigger an inflammatory response in the vaginal tissues, leading to increased white blood cell activity and cytokine production, which can contribute to the symptoms of BV.

It’s important to note that while Gardnerella vaginalis is a key player in BV development, it is often found in the vaginal flora of many women without causing any symptoms or issues. Therefore, the pathogenicity of G. vaginalis may depend on other factors, such as host immunity, the presence of other bacterial species, and individual susceptibility.

Lab Diagnosis

The laboratory diagnosis of Gardnerella vaginalis typically involves a combination of clinical evaluation, microscopic examination, and specific laboratory tests. Here are the main methods used for the diagnosis:

  1. Clinical Evaluation: The first step in diagnosing G. vaginalis infection is a thorough clinical assessment by a healthcare provider. The doctor will inquire about the patient’s medical history, symptoms, sexual activity, and any other relevant information. Typical symptoms of Gardnerella vaginalis infection include abnormal vaginal discharge (grayish-white), a fishy odor, and sometimes itching or irritation.
  2. Microscopic Examination: A wet mount (saline or potassium hydroxide preparation) of the vaginal discharge may be examined under a microscope. It appears as small, pleomorphic (variable shape) Gram-variable rods or cocci. Clue cells, which are vaginal epithelial cells covered with adherent bacteria, are a hallmark of BV and often indicate the presence of Gardnerella vaginalis.
  3. Whiff Test: A whiff test can be performed by adding a drop of 10% potassium hydroxide (KOH) solution to a sample of vaginal discharge on a glass slide. A characteristic fishy odor is produced when KOH interacts with the volatile amines produced by G. vaginalis and other bacteria in BV.
  4. Culture: It can be cultured on selective media in the laboratory. However, its fastidious nature and slow growth make culture-based methods less practical for routine diagnosis. Culture may be reserved for research purposes or when specific antibiotic susceptibility testing is required.
  5. Nucleic Acid Amplification Tests (NAATs): Polymerase chain reaction (PCR) or other nucleic acid amplification tests can detect the DNA or RNA of Gardnerella vaginalis in vaginal swab samples with high sensitivity and specificity. These molecular methods are increasingly used in clinical settings due to their accuracy and speed in diagnosing BV.
  6. Nugent Scoring: Nugent scoring is a Gram stain-based method used to quantify the vaginal microbiota and identify BV. It evaluates the relative abundance of lactobacilli, Gardnerella vaginalis, and other bacterial morphotypes. A high Nugent score (7-10) indicates BV.
  7. Amsel Criteria: The Amsel criteria are a set of clinical criteria used to diagnose BV based on four specific features: 1) thin, grayish-white vaginal discharge; 2) positive whiff test; 3) presence of clue cells on microscopy; and 4) vaginal pH above 4.5. If three of these criteria are met, BV is diagnosed.


The treatment of Gardnerella vaginalis infection primarily involves the management of bacterial vaginosis (BV), the condition caused by the overgrowth of Gardnerella vaginalis and other harmful bacteria in the vaginal flora. Treatment aims to restore the normal balance of vaginal bacteria and alleviate symptoms. It is essential to consult a healthcare provider for an accurate diagnosis and appropriate treatment plan. Here are the main treatment options for Gardnerella vaginalis:

  1. Antibiotics: The most common and effective treatment for BV is the use of antibiotics. The two main antibiotics used are:a. Metronidazole: It can be administered orally as tablets or capsules, or topically as a gel or cream. A typical oral dose is 500 mg twice daily for 7 days, or a single 2 g dose. The topical formulations are used intravaginally.b. Clindamycin: Clindamycin is an alternative antibiotic option for BV treatment. It is available as a cream that is applied intravaginally.
  2. Recurrent BV: Recurrence of BV is common, and in some cases, it may be necessary to use extended or repeated courses of antibiotics. For recurrent BV, longer treatment regimens or maintenance therapy with lower doses of antibiotics might be prescribed.
  3. Partner Treatment: It is generally not necessary to treat male sexual partners for BV, as the condition is not considered a sexually transmitted infection. However, in cases of recurrent BV, some providers may consider treating male partners to help reduce the risk of reinfection.
  4. Probiotics: Some studies have explored the use of probiotics (beneficial bacteria) to restore the vaginal microbiota and prevent BV recurrence. Probiotic supplements containing specific strains of lactobacilli may be prescribed or recommended by healthcare providers.
  5. Avoiding Triggers: Avoiding potential triggers that might disrupt the vaginal flora, such as excessive douching, scented feminine hygiene products, and unprotected sexual activity with multiple partners, may help reduce the risk of BV recurrence.

It is crucial to complete the full course of antibiotics as prescribed, even if symptoms improve before the treatment period is over. If symptoms persist or recur after treatment, it is essential to follow up with a healthcare provider for further evaluation and management.


Preventing Gardnerella vaginalis and bacterial vaginosis (BV) involves maintaining a healthy vaginal environment and promoting a balanced vaginal microbiota. While it may not always be possible to completely prevent BV, the following measures can help reduce the risk of its development:

  1. Practice Good Hygiene: Maintain proper genital hygiene by cleaning the external genital area with mild soap and water. Avoid using douches or harsh cleansers inside the vagina, as they can disrupt the natural balance of bacteria.
  2. Avoid Irritants: Avoid using scented soaps, perfumed lotions, and other products with harsh chemicals in the genital area. These can disrupt the vaginal flora and increase the risk of BV.
  3. Limit Antibiotic Use: Unnecessary or prolonged use of antibiotics can disrupt the balance of vaginal bacteria. Only take antibiotics when prescribed by a healthcare professional and follow their instructions carefully.
  4. Practice Safe Sex: While BV is not considered a sexually transmitted infection, using condoms during sexual intercourse can reduce the risk of introducing harmful bacteria and disrupting the vaginal environment.
  5. Limit Sexual Partners: Having multiple sexual partners may increase the risk of developing BV. Limiting the number of sexual partners can help reduce the chances of exposure to new bacterial strains.
  6. Probiotics: Some studies suggest that using vaginal probiotics or consuming probiotic-rich foods may help maintain a healthy vaginal microbiota. Probiotics contain beneficial bacteria, such as lactobacilli, which can help inhibit the growth of harmful bacteria like Gardnerella vaginalis.
  7. Regular Checkups: Regular gynecological checkups can help detect any vaginal imbalances or infections early on, allowing for timely treatment and management.
  8. Manage Chronic Conditions: If you have diabetes or other chronic health conditions, work with your healthcare provider to manage them effectively. Some chronic conditions can increase the risk of BV.
  9. Avoid Vaginal Practices with Little Evidence: Some practices, such as the use of vaginal steaming or other alternative treatments, lack scientific evidence and may be harmful or disrupt the vaginal flora.


Keynotes on Gardnerella vaginalis:

  1. Gardnerella vaginalis is a Gram-variable bacterium, considered a facultative anaerobe, and is the primary causative agent of bacterial vaginosis (BV) in women of reproductive age.
  2. BV is characterized by an imbalance in the vaginal microbiota, leading to an overgrowth of G. vaginalis and other harmful bacteria, which can cause symptoms like abnormal vaginal discharge (grayish-white), a fishy odor, and sometimes itching or irritation.
  3. The bacterium is pleomorphic, meaning it can change its shape and size, making its identification challenging under conventional microscopy.
  4. Diagnosis of Gardnerella vaginalis infection is often confirmed through clinical evaluation, microscopic examination of vaginal discharge for clue cells, and laboratory tests like nucleic acid amplification tests (NAATs) or Nugent scoring based on Gram staining.
  5. The pathogenicity of G. vaginalis involves biofilm formation, metabolic changes that alter vaginal pH, production of toxic substances (biogenic amines), and disruption of the normal vaginal flora.
  6. Treatment of Gardnerella vaginalis infection typically involves antibiotics, such as metronidazole or clindamycin, which aim to restore the balance of vaginal bacteria and alleviate symptoms of BV.
  7. Preventive measures for G. vaginalis and BV include maintaining good genital hygiene, avoiding irritants and harsh products, practicing safe sex, limiting antibiotic use, and considering the use of probiotics to promote a healthy vaginal microbiota.
  8. BV is not considered a sexually transmitted infection (STI), but it may be associated with sexual activity and changes in sexual partners.
  9. Recurrence of BV is common, and extended or repeated courses of antibiotics or maintenance therapy might be necessary for managing recurrent BV.
  10. If experiencing any vaginal symptoms or concerns, it is essential to seek medical advice from a healthcare provider for accurate diagnosis and appropriate management.

Further Readings

  1. Sobel, J. D. (2000). Bacterial vaginosis. Annual Review of Medicine, 51, 349-356. DOI: 10.1146/
  2. Hillier, S. L., & Holmes, K. K. (1988). Bacterial vaginosis. In K. K. Holmes, P. F. Sparling, P. A. Mardh, et al. (Eds.), Sexually Transmitted Diseases (2nd ed., pp. 547-560). New York, NY: McGraw-Hill.
  3. Menard, J. P., Fenollar, F., & Henry, M. (2011). Molecular diagnosis of bacterial vaginosis: An update. Journal of Clinical Microbiology, 49(4), 885-891. DOI: 10.1128/JCM.02242-10
  4. Bradshaw, C. S., & Sobel, J. D. (2016). Current treatment of bacterial vaginosis—limitations and need for innovation. The Journal of Infectious Diseases, 214(Supplement_1), S14-S20. DOI: 10.1093/infdis/jiw143
  5. Peebles, K., & Velloza, J. (2019). Impact of bacterial vaginosis on women’s health and well-being. American Journal of Obstetrics & Gynecology, 220(4), 324-330. DOI: 10.1016/j.ajog.2018.12.023
  6. Verstraelen, H., Verhelst, R., & Claeys, G. (2009). Bacterial vaginosis: an update on diagnosis and treatment. Expert Review of Anti-Infective Therapy, 7(9), 1109-1124. DOI: 10.1586/eri.09.87
  7. Machado, A., Cerca, N., & Requena, O. (2013). Pathogenesis of bacterial vaginosis: discussion of current hypotheses. The Journal of Infectious Diseases, 208(9), 1382-1383. DOI: 10.1093/infdis/jit315
  8. Petricevic, L., & Witt, A. (2012). The role of Lactobacillus casei rhamnosus Lcr35 in restoring the normal vaginal flora after antibiotic treatment of bacterial vaginosis. BJOG: An International Journal of Obstetrics & Gynaecology, 119(7), 831-836. DOI: 10.1111/j.1471-0528.2012.03325.x

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