Assessment of Vaginal Lactobacillary Flora in Wet Mount and Fresh or Delayed Gram's Stain

Objective: The assessment of the vaginal lactobacillary flora helps to direct further diagnostic microbiologic investigations in genital infectious disease and seems to represent a powerful tool in predicting infectious morbidity and preterm labor during pregnancy. In the absence of a "gold standard," we studied the variations in assessing lactobacillary morphotypes according to the method used.

Methods: The lactobacillary flora from 183 pregnant women was classified according to 3 groups: normal, intermediate, and abnormal. This grading of lactobacilli was appled to vaginal and cervical specimens by means of 1) immediate wet-smear microscopy, 2) Gram's stain on a fresh, air-dried specimen, and 3)delayed Gram's stain after specimen transportation in Stuart's growth medium for 3-6 h.

Results: The assignment of intermediate or abnormal flora (grade II or grade III) showed high concordance rates among the different preparatory techniques, but the assignment of grade I (normal flora) did not. Fewer lactobacilli were found 2.6 times more often after Gram's stains of fresh specimens [Relative Risk (RR) 2.6, 95% confidence interval (CI) 1.7-4.1] and 6 times more often when the Gram%s stain was performed in a delayed examination after transport than in a fresh wet-mount specimen (RR 6.2, 95% CI 2.5-15.6). Disturbed lactobacillary grades were also found more frequently in specimens from the cervix than those from the vagina (RR 4.0, 95% CI, 1.5-10.4).

Conclusions: There are discrepancies in the diagnosis of lactobacillary grades between gram-stained and fresh vaginal specimens. The evidence is ambiguous as to which of the 2 methods is responsible. If an evaluation is to be done on a gram-stained specimen, then the storage of the sample in Stuart transport medium before staining should be avoided.