Bacterial Vaginosis (BV) is a condition representing a disruption in the natural balance of the vaginal microbiome. This shift involves a significant change in the types and numbers of bacteria present. Microscopic examination of a vaginal fluid sample is the standard method used to confirm this bacterial imbalance. The visual findings under the microscope provide evidence of the specific cellular and microbial changes characteristic of the condition.
Preparing the Sample for Viewing
The first step in microscopic diagnosis involves preparing a simple slide known as a “wet mount” or “wet prep.” A small sample of vaginal discharge is collected using a cotton swab during a pelvic examination. This procedure allows for immediate analysis of the living, unaltered cellular environment.
The collected fluid is immediately mixed with a drop of normal saline solution on a glass slide, then covered with a thin coverslip. Using saline prevents the cells and bacteria from drying out, keeping them visible in their natural state. The specimen is examined under a microscope at both low (100x) and high (400x) power magnification, with high power used to visualize the fine detail of the bacteria and cells.
Identifying the Diagnostic Clue Cells
The most distinctive visual marker for BV under the microscope is the presence of “clue cells.” These are normal vaginal epithelial cells that have been completely coated with bacteria. A healthy epithelial cell has a smooth, well-defined border and a visible central nucleus.
In contrast, a clue cell appears hazy, indistinct, or roughened because bacteria are densely adhered to its surface. This heavy coating is often described as creating a “stippled” or “shaggy” appearance, which effectively obscures the cell’s clear outer edges. The finding of numerous epithelial cells covered in this manner strongly suggests the diagnosis.
The bacteria adhere so thickly that they create a granular texture over the cell, making the nucleus appear less distinct against the background haze. The epithelial cells themselves are large, flat cells shed from the vaginal lining. The presence of numerous clue cells in the wet mount is considered a microscopic sign that the cellular environment has been overwhelmed by BV-associated organisms.
Observing the Bacterial Population Shift
Beyond the distinctive clue cells, the overall bacterial landscape of the fluid sample shows a population shift. In a healthy vaginal environment, the field is dominated by large, protective, rod-shaped bacteria known as Lactobacilli. These bacteria are easily identifiable as long, chunky rods, often measuring between 5 and 15 micrometers in length.
In the presence of BV, these dominant Lactobacilli rods are either significantly reduced or entirely absent from the microscopic field. Their disappearance creates a void rapidly filled by a high concentration of much smaller, more diverse bacterial forms, including a proliferation of various coccobacilli and curved rods.
These smaller, diverse bacteria often appear under the microscope as a dense, uniform “haze” or “swarm” across the background of the slide. This increase in the population of small, mixed bacteria, alongside the loss of the large protective rods, confirms the microbial imbalance that defines bacterial vaginosis. The combination of this dense overgrowth and the presence of clue cells provides the evidence necessary for diagnosis.