Vaginal swab

Clinical significance
The vagina, which is sterile at birth, is rapidly colonised within 12-24 hours by staphylococci, streptococci and diphtheroids; within two to three days, under the influence of maternal oestrogens, it is colonised by lactobacilli. Once the maternal oestrogens have gone, the lactobacilli disappear from the vaginal epithelium, and as a result the vaginal pH tends to be alkaline (6-8) until puberty. From puberty and throughout the reproductive years, the woman’s own oestrogens again cause glycogen to be deposited, allowing stable colonisation by lactobacilli, which ferment the glycogen and produce lactic acid, acidifying the vagina to a pH between 3 and 5. This acidity, which hinders the growth of bacteria from outside (which prefer a neutral environment), is an important natural defence. After the menopause, as oestrogen levels fall, a situation similar to that before puberty returns, with an alkaline pH, loss of lactobacilli and the presence of anaerobic bacteria, Gram-positive cocci and Enterobacteriaceae.
Microbiological examination of vaginal discharge by microscopy and culture can show the presence of fungi (yeasts) and of bacterial vaginosis, which is characterised by the appearance of Gardnerella vaginalis, a bacterium that coats the epithelial cells in a characteristic way (these are therefore called clue cells), and by a reduction in lactobacilli with a corresponding increase in other anaerobic flora. In particular cases, staphylococci and Haemophilus are also looked for. For Trichomonas vaginalis testing, see the corresponding entry.