Bacterial vaginosis: what is physiological in vaginal bacteriology? An update and opinion.

Bacterial vaginosis (BV) was originally described as a sexually transmitted infection caused by a single microbe. The prevailing concept describes BV as a polymicrobial coitus-associated disease of uncertain origin. In this overview the natural history of BV as a monobacterial and polymicrobial entity is examined with respect to the physiological concept of BV in relation to sexual behavior before and after introduction of the hormonal contraceptive pill. Bacterial vaginosis, characterized by low vaginal acidity (elevated pH) and replacement of vaginal Lactobacillus by Gardnerella vaginalis flora, could be caused by unprotected intercourse when a low pH changes through the neutralizing power of male ejaculate, vaginal coital transudate and vaginal neurogenic transudate. A monobacterial form, G. vaginalis vaginitis, could be a physiological post-coital condition for protection of ejaculated spermatozoa, characterized by 'pure'Gardnerella flora and elevated pH as an immediate result of an incidental unprotected coital act through neutralization of vaginal acid and replacement of Lactobacillus by Gardnerella flora. A polymicrobial form of BV could be autoinfection of the post-coital physiological G. vaginalis flora, characterized by a mixture of G. vaginalis, Mycoplasma hominis and anaerobic bacteria at lower vaginal acidity, possibly resulting from suppression of normal vaginal acidity through repeated sexual acts, with a resultant higher pH and transfer of enteric bacteria from the perianal region. Monobacterial and polymicrobial auto-infectious forms of BV may be clinically distinct and share a common origin. The understanding of BV as a basic physiological entity could influence the prophylaxis and treatment of the largely therapy-resistant polymicrobial BV.