Abstract: Objective   To investigate the relation of Mycoplasma hominis symbiosis and the resistence of Trichomonas vaginalis to metronidazole.  Methods  From November 2010 to July 2011, 160 isolates of T. vaginalis were collected from the genital tract secretion of gynecological out-patients at the Sichuan Provincial Hospital for Women and Children. The minimum lethal concentration (MLC) to metronidazole of these isolates was determined by an in vitro sensitivity assay with different concentration gradients of metronidazole (from 1 to 1 024 μg/ml), and M. hominis DNA in T. vaginalis was detected by polymerase chain reaction (PCR) technique with specific 16S rRNA primers. After clearance of M. hominis from the parasites by 32 μg/ml doxycycline, MLC was determined and compared with that before clearance.  Results  MLC of metronidazole in T. vaginalis ranged from 1 to 256 μg/ml, with 61.3% isolates (98/160) ranging from 1 to 8 μg/ml, 26.3% isolates (42/160) ranging from 16 to 32 μg/ml, and 12.5% isolates (20/160) ranging from 64 to 256 μg/ml. 61 isolates were PCR positive for M. hominis DNA in the 160 isolates of T. vaginalis. The M. hominis DNA positive rate was significantly higher in the T. vaginalis isolates with higher MLC than those isolates with lower MLC (P<0.01). However, when M. hominis was cleared by doxycycline from 8 isolates among the 61 ones, no change was observed in sensitivity of the isolates to metronidazole.  Conclusion  M. hominis symbiosis might be associated with the metronidazole-resistance of T. vaginalis.  However, it needs direct evidence.

Key words: Trichomonas vaginalis, Mycoplasma hominis, Symbiosis, Metronidazole, Drug resistance