Pathogenesis of abnormal vaginal bacterial flora

This study was undertaken to determine the relationships between microscopy findings on wet mounts, such as lactobacillary grade or vaginal leukocytosis, and results of vaginal culture, lactate and succinate content of the vagina, and levels of selected cytokines.

In a population of 631 unselected women seeking treatment at an obstetrics and gynecology outpatient clinic, vaginal fluid was obtained by wooden Ayre spatula for wet mounting and pH measurement, by high vaginal swab for culture, and by standardized vaginal rinsing with 2 mL 0.9% sodium chloride solution for measurements of lactate, succinate, interleukin 1beta, interleukin 8, leukemia inhibitory factor, and interleukin 1 receptor antagonist concentrations. Lactate and succinate levels were measured by gas-liquid chromatography and the cytokine concentrations were measured by specific immunoassays. Both univariate analysis (Student t test, Welch test, chi(2) test, and Fisher exact test) and multivariate regression analysis (Cox analysis) were used.

Increasing disturbance of the lactobacillary flora (lactobacillary grades I, IIa, IIb, and III) was highly correlated with the presence of Gardnerella vaginalis, Trichomonas vaginalis, enterococci, group B streptococci, and Escherichia coli. Vaginal pH and interleukin 8 and interleukin 1beta concentrations increased linearly with increasing lactobacillary grade, whereas lactate concentrations and the presence of epithelial cell lysis decreased. A similar pattern of associations with increasing leukocyte count was clear, but in addition there was an increase in leukemia inhibitory factor concentration. Multivariate analysis of vaginal leukocytosis, lactobacillary grades, and the presence of positive vaginal culture results showed that interleukin 1beta concentration was most closely related to the lactobacillary grade, leukemia inhibitory factor concentration was most closely related to the lactobacillary grade and positive culture results, interleukin 8 concentration was most closely related to positive culture results, and interleukin 1 receptor antagonist concentration was most closely related to vaginal leukocytosis and positive culture results. The concentration ratio of interleukin 1beta to interleukin 1 receptor antagonist remained stable, except when vaginal leukocytosis increased. In its most severe form, with >10 leukocytes per epithelial cell present, a decompensation of the vaginal flora with a collapse in interleukin 1beta and interleukin 1 receptor antagonist concentrations was seen, but there was a concurrent sharp increase in leukemia inhibitory factor concentration. This pattern was completely different from the course of the cytokine concentrations associated with a lactobacillary grade increase.

Both disturbed lactobacillary grade and the presence of increasing vaginal leukocytosis were correlated with lactobacillary substrate (lactate) concentration, pH, and the concentrations of a variety of cytokines. There was a remarkably linear increase in these cytokines as either leukocytosis or lactobacillary grade became more severe. In circumstances in which leukocytosis was extreme, however, interleukin 1beta was no longer produced but leukemia inhibitory factor concentrations increased. We speculate that in extreme inflammation the body tries to limit the damage that can be done by exaggerated cytokine production.