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Bacterial Vaginosis: A Coat of Many Colors

July 9, 2013

Felix Martinez, Jr., M.D.

The vaginal microbiome is a dynamic ecosystem normally inhabited by a variety of microorganisms.  Several species of lactobacilli and a host of other organisms comprise the normal vaginal microflora, the composition which is not static, changing over time in response to endogenous and exogenous influences.  

BV ClinicalLactobacilli help support healthy vaginal conditions by maintaining an acidic environment that is inhospitable to other pathogenic microorganisms.  Lactic acid produced by lactobacilli maintains vaginal pH between 3.8 and 4.2, a range favorable for growth of more lactobacilli.  A healthy, balanced microbiome prevents colonization by other pathogens, some of which can establish tough cellular biofilms that promote overgrowth of offending bacteria.  A biofilm is illustrated in Figure 1.  Examples of organisms which offend by overgrowth are Gardnerella vaginalis and Atopobium vaginae.


Figure 1. Purple Staining of Biofilm

The most common alteration of the normal flora is a condition termed Bacterial Vaginosis (BV).

FactorsThe composition of the vaginal microflora can be altered by various influences, including antibiotic use, contraceptives, pregnancy, chronic health conditions, and infections.

BV is characterized by a change in the normal microbiological order of the vagina, with associated loss of protective lactobacilli and concomitant overgrowth of anaerobic and facultative bacteria.  

The first step in the pathogenesis of BV is thought to be related to a depletion of lactobacilli from the vaginal flora.   The precise mechanism of how lactobacilli populations are altered and then replaced by BV-associated bacteria in women having complaints of BV is still unknown, but the result is a change in vaginal pH.

BV OrganismsOrganisms described to be indicative diagnostic biomarkers of BV are listed in Table 1.  Since these organisms can also be found in subjects who do not have BV, they are not specific markers for disease, and illustrate why bacterial culture of vaginal fluid has not proven useful for the diagnosis of BV.  Further, the disease state for women having this condition is termed ‘vaginosis‘ (condition of) not ‘vaginitis’ (in-flammation/infection of).  The bacteria associated with a disease state could, more rightly, be termed “marker organisms” and not necessarily “infecting pathogens”.

Bacterial vaginosis, therefore, is an example of polymicrobial disease causation due to the interplay and metabolic interdependence of several bacterial species in the vaginal microenvironment.

In BV, Koch’s postulates (Table 2) for establishing disease causation have yet to be fulfilled for any bacterium or group of bacteria.  In addition, although the BV responds to treatment with antibiotics such as metronidazole and clindamycin, metronidazole paradoxically has a low level of in vitro activity against Atopobium vaginae and Mobiluncus sp., adding to the confusion in classifying and treating this disorder.  Since disease causation by an entire microbial community defies use of Koch’s postulates and their traditional applications in disease causation, the rate of relapse and persistence of BV that occurs is not surprising, even after antibiotic treatment.

Kochs Postulates

Simply stated, the causes and pathogenesis of bacterial vaginosis remain poorly understood, and clinical management of the condition can be challenging.

Risks and Annoyances

Women with BV have a three- to four-fold higher risk for being infected by Chlamydia trachomatis and Neisseria gonorrhoeae.1  They are also at higher risk for HIV infection.2  Women with BV who undergo invasive surgery such as hysterectomy or abortion suffer from post-operative infections two to three times more often than women without BV.3 BV has been associated with pelvic inflammatory disease4 and endometritis.5  Accurate diagnosis and appropriate treatment of BV is especially critical for pregnant women, where the disease is associated with a five-fold increased risk for late miscarriage and pre-term birth.6  Finally, BV is an unpleasant and not uncommon condition that women – especially when recurrent – expect efficacious results as a result of their office visit.


Application of Amsel criteria7 has been helpful in immediate triage of women with vaginal discharge.  Amsel criteria are listed in Table 3.

Amsel Criteria

Nugent’s criteria8were established to provide metrics in evaluation of wet mount preparations of vaginal discharge fluids (see illustration in Table 4).  Nugent’s criteria measure specific Gram-stained bacterial morphotypes.  Consequently, organisms that do not absorb Gram stain (such as ureaplasmas and mycoplasmas) are not measured.

Nugent Score

Both the Amsel criteria and Nugent scoring approaches suffer from subjective interpretation and limitations and, as has been shown in multiple studies, do not  necessarily perfectly agree with one another. Up to half of all women who meet the diagnostic criteria for BV do not exhibit clinical symptoms.

Thus, because of shortcomings of wet mount microscopy, and the limitations of Amsel’s criteria and Nugent’s scoring, there has been much work applied to development of better and more objective testing for vaginosis and vaginitis.

The development of molecular techniques of identification in microbiology has allowed for the development of culture-independent molecular diagnostics as well as the identification of new organisms associated with BV.  Many of these new BV-associated organisms are found in the gastrointestinal tract, suggesting that BV may be an endogenous infection.

Recently, the utility of molecular techniques has been demonstrated using polymerase chain reaction (PCR) testing for the major bacterial species inhabiting the vaginal environment of healthy women and BV carriers.  Results of PCR assessment of BV-related bacteria correlates significantly with a high sensitivity and specificity to Nugent scoring and, to a lesser extent, with Amsel criteria in the diagnosis of BV. Application of molecular methods for characterization of vaginal microflora in BV patients has thereby become a useful and accepted practice and is a major trend in laboratory diagnostics.

In summary, a new tool – a very good one – is available for the evaluation of women with bacterial vaginosis and vaginitis and can be ordered on vaginal swabs through Incyte Diagnostics.  Sensitive and specific results allow for selective antibiotic use in the treatment of vaginal signs and symptoms.  Molecular infectious disease testing on vaginal swabs offers high sensitivity and specificity and represents an exciting advance which allows for selective antibiotic treatment and higher treatment success  with patients who have vaginal signs and symptoms.

1 Wiesenfeld HC, et al. 2003. Bacterial vaginosis is a strong predictor of Neisseria gonorrhoeae and Chlamydia trachomatis infection. Clin Infect Dis 36:663-668.
2 Atashili J, Poole C, Ndumbe PM, Adimora AA, Smith JS. 2008. Bacterial vaginosis and HIV acquisition: a meta-analysis of published studies. AIDS 22:1493-1501.
3 Larsson PG, et al. 2005. Bacterial vaginosis. Transmission, role in genital tract infection and pregnancy outcome: an enigma. APMIS 113:233- 245.
4 Ness RB, et al. 2005. A cluster analysis of bacterial vaginosis-associated microflora and pelvic inflammatory disease. Am J Epidemiol 162:585-590.
5 Andrews WW, et al. 2006. Assoc of asymptomatic bacterial vaginosis with endometrial microbial colonization & plasma cell endometritis. Am J Obstet Gynecol 195:1611- 1616.
6 Denney JM, Culhane JF. 2009. Bacterial vaginosis: a problematic infection from both a perinatal and neonatal perspective. Semin Fetal Neonatal Med 14:200-203.
7 Gutman RE, Peipert JF, Weitzen S, Blume J. Evaluation of clinical methods for diagnosing bacterial vaginosis. Obstet Gynecol 2005;105:551–6.
8 Nugent RP, et al. Reliability of diagnosing bacterial vaginosis is improved by a standardized Gram stain interpretation. J Clin Microbiol 1991;29:297–301.

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