Wet mount microscopy reflects functional vaginal lactobacillary flora better than Gram stain

Gilbert G G Donders¹, Annie Vereecken², Alfons Dekeersmaecker², Ben Van Bulck³ and Bernard Spitz¹

¹ Department of Obstetrics and Gynecology, Gasthuisberg University Hospital, Katholieke Universiteit, Herestraat 47, 3000 Leuven, Belgium
² Laboratory of Clinical Pathology, Americalei 63, 2000 Antwerp, Belgium
³ Department of Gynecology, Erasmus Hospital, 2000 Antwerp, Belgium

Correspondence to:
Dr Donders

Aim—The status of vaginal lactobacillary flora, an indicator of possible genital infection and pregnancy complications, can be assessed on wet mount or Gram stained specimens. The former is quick, the latter more routine. The accuracy of the two preparative techniques to detect normal vaginal lactobacillary microflora was compared for 646 patients. The effect of delay in transport medium before Gram staining was also investigated.

Methods—Patients presented with infectious vaginitis or for a routine prenatal visit. After placement of a speculum, duplicate smears were taken from the upper vaginal vault and examined fresh or after Gram staining. Lactobacillary grades from both methods were compared with lactate concentration in vaginal rinses. In a subgroup of 238 patients, Gram staining was performed both on fresh smears and those that had been transported in Stuart's growth medium.

Results—Higher lactobacillary grades (more disrupted flora) were diagnosed 2.9 times more frequently on Gram stained specimens than on wet mounts (p < 0.0001), a difference even more pronounced after transport in Stuart's medium (relative risk, 4.2; p < 0.0001). Lactobacillary grades assessed on wet mounts correlated better with vaginal lactate concentration than those assessed on Gram stains.

Conclusions—Easier recognition of lactobacillary morphotypes on wet mounts than on Gram stains might result from the loss of lactobacilli by the process of fixation or Gram staining. Wet mount microscopy of vaginal smears for assessment of lactobacillary grades, rather than Gram staining, is strongly recommended.

Key Words: Gram stain • vaginal smears • wet mounts • lactobacillary flora

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