O02.2 Susceptiblity of Bacterial Vaginosis (BV)-Associated Bacteria and Lactobacilli to Rifaximin, Metronidazole and Clindamycin

Abstract

ObjectiveRifaximin is a semisynthetic rifamycin with poor oral bioavailability, used as an oral agent for the treatment of traveller’s diarrhoea and hepatic encephalopathy. Rifaximin is in development as a topical agent for the treatment of bacterial vaginosis (BV). The objective of this study was to evaluate the antimicrobial susceptibility of vaginal isolates of facultative and anaerobic bacteria to rifaximin, clindamycin and metronidazole.MethodsA total of 411 unique BV-related bacteria and 100 isolates of lactobacilli recovered from the human vagina of US women during the years 2009–2012 were tested for antimicrobial susceptibility by the agar dilution CLSI reference method to calculate MICs.ResultsOverall, 142 (35%) of the BV-associated vaginal isolates tested were resistant to metronidazole, 63 (15%) were resistant to clindamycin and 11 (2.6%) were resistant to rifaximin. Metronidazole resistance was observed most frequently amongGardnerella vaginalis(n = 100 isolates, 69% resistant),Atopobium vaginae(n = 62, 87% resistant) andMobiluncus(n = 40, 42% resistant), whereas most were susceptible to both clindamycin (197/202; 98% susceptible) and rifaximin (191/202; 95% susceptible). Both rifaximin and metronidazole were effective against all strains ofPrevotella bivia(n = 34),P timonensis(n = 33),Anaerococcus tetradius(n = 21), Finegoldia magna(n = 20) andPeptoniphilus lacrimalis(n = 20), whereas clindamycin resistance was detected among 74%, 42%, 19%, 30% and 30% of these anaerobes isolates, respectively. More than 90% ofPrevotella amnii(n = 33),Peptoniphilus harei(n = 23) andMegasphaera-like bacteria (n = 25) were susceptible to all three antibiotics. As expected, none of theLactobacillusisolates were susceptible to metronidazole, whereas a majority were susceptible to both clindamycin and rifaximinin vitro.ConclusionRifaximin had MIC values for a range of microorganisms associated with BV which were superior or similar to the other two drugs approved for the treatment of this condition and deserves clinical evaluation as a new therapeutic agent for the treatment of BV.