Reduction of Trimethylamine Oxide to Trimethylamine by Mobiluncus Strains Isolated from Patients with Bacterial Vaginosis

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Abstract
The reduction of trimethylamine oxide (TMAO) to trimethylamine (TMA) by bacteria is the main source of the unpleasant odour of rotting fish. The presence of TMA in the vaginal discharges of patients with Bacterial Vaginosis (BV) has been correlated with the unpleasant ‘fishy’ odour associated with this condition. Gardnerella spp., Mobiluncus spp., and Bacteroides spp. are found in the vaginal discharge of women with BV in much larger numbers than in asymptomatic women. Three strains of mobiluncus were isolated from clinical cases of BV and all reduced TMAO to TMA. Some also produced smaller amounts of TMA from choline. Gardnerella spp. and Bacteroides spp. isolated from BV did not reduce TMAO to TMA. One bacteroides isolate reduced choline to TMA. None of the isolates produced TMA from betaine, histidine or arginine. Both the growth rate and yield of mobiluncus were stimulated by the addition of TMAO to the complex medium required by the organism. TMAO was converted quantitatively to TMA, which was not further metabolised. Cytochromes were detected in Mobiluncus spp., but their role in the reduction of TMAO to TMA (if any) was not determined.