In bacterial vaginosis (BV), hydrogen peroxide+ lactobacilli (LB), which define normal vaginal microbiology, are replaced by anaerobic/facultative bacteria.¹ BV is the most common cause of vaginitis and associated with preterm delivery, pelvic inflammatory disease and HIV acquisition.^2,3 Its cause is unknown. Treatment with metronidazole, clindamycin or tinidazole improves symptoms and restores normal flora and associated mucosal defences,^4,5 but BV frequently persists (11–29%) and recurs (72% by 7 months).^6–8 Unprotected sex may contribute.^7,9 In fact, the debate about sexual transmission of a potentially causative agent for BV has been given new urgency by the report of newly defined Clostridiales bacteria detected, along with other novel BV-associated bacteria (such as Atopobium vaginae), which appear to be highly specific for BV—that is, they appear to be present rarely in women without BV.^10,11 Newer data also support a role for BV in promoting HIV acquisition in women.¹² The prevalence of BV in lesbians has been reported to be high (25–52%) in several studies and most female sex partners are concordant for …