Identification and preliminary characterization of a cytotoxin isolated from Mobiluncus spp.

Mobiluncus curtisii and M. mulieris are anaerobic curved rods commonly isolated, together with other bacteria, from the vagina of women with bacterial vaginosis (BV). We have shown that of 11 strains of M. curtisii and four strains of M. mulieris examined, each produced a cytotoxin after growth in three types of liquid media. The toxin present in supernatant fluids after centrifugation of Mobiluncus cultures was active against Vero cells and four other cell lines tested, producing a marked cytopathic effect with destruction within 72 hours. The supernatant fluids could be diluted no more than 8 to 16-fold before toxic activity was lost. In bovine oviduct organ cultures, the supernatant fluids from cultures of eight M. curtisii and two M. mulieris strains that were tested caused loss of ciliary vigour which was usually complete after 60 hours. In addition, there was raggedness of the epithelial cell border with detachment of cells seen histologically and loss of cilia together with bloating and loss of ciliated cells observed by scanning electron microscopy. The toxin was extracellular, relatively thermostable (surviving heating to 56 degrees C for 30 min but not boiling for 20 min) and was inactivated under extremes of pH (pH 9 and pH 3). The existence of the toxin means that the Mobiluncus spp could have an active role in the development of BV.