Trichomonas vaginalis Susceptibility Testing

Susceptibility Testing

Susceptibility testing is conducted by broth microdilution for both metronidazole and tinidazole. Susceptibility data are reported as the minimum lethal concentration (MLC) which is defined as the lowest antimicrobial concentration that results in loss of parasite motility in culture.

Currently there are no established breakpoints for metronidazole and tinidazole in T. vaginalis. CDC is making MLC distribution data available online to aid in the interpretation of Trichomonas susceptibility testing results. These downloadable data contain tables and graphic representations that display MLC distributions for isolates collected from 48 successfully treated individuals, 47 individuals with infections that were refractory to treatment with metronidazole, and 33 individuals who were refractory to treatment with tinidazole. Isolates with MLCs ≥ 50 µg/ml for metronidazole and ≥ 6.3 µg/ml for tinidazole were associated with treatment failure ⁽¹⁾. CDC will continue to expand this database to include additional data as additional studies are conducted.

Trichomonas vaginalis Clinical Management and Consultation

The CDC Division of STD Prevention provides recommendations on the treatment of various sexually transmitted diseases including Trichomoniasis – STI Treatment Guidelines (cdc.gov). For clinical guidance with the management of recurrent or persistent trichomoniasis, please contact the CDC Division of STD Prevention Trichomonas Clinical Consultation team at TVconsultation@cdc.gov. Susceptibility testing may be helpful in selection of alternative treatment regimens ^{(2, 3)}.

References

1. Augostini P, Bradley ELP, Raphael BH, Secor WE. In Vitro Testing of Trichomonas vaginalis Drug Susceptibility: Evaluation of Minimal Lethal Concentrations for Metronidazole and Tinidazole That Correspond With Treatment Failure. Sex Transm Dis. 2023;50(6): 370-373.
2. Bosserman EA, Helms DJ, Mosure DJ, Secor WE, Workowski KA. Utility of antimicrobial susceptibility testing in Trichomonas vaginalis-infected women with clinical treatment failure. Sex Transm Dis. 2011;38(10):983-987.
3. Workowski, KA, Bachmann, LH, Chan, PA, Johnston, CM, et al. Sexually Transmitted Infections Treatment Guidelines, 2021. MMWR Recomm Rep 2021;70(No. RR4): 1-187.