Introduction Syndromic management is used to control sexually transmitted diseases in South Africa. Trichomonas vaginalis causes trichomoniasis which results in vaginal discharge in symptomatic patients. This is treated with metronidazole which is included in the syndromic management antimicrobial regime. In order for this regime to be effective, the organisms causing each syndrome and their antimicrobial susceptibility profile need to be evaluated periodically to ensure that the most appropriate antimicrobial agents are included.

Methods Women 18 years and older presenting with vaginal discharge were recruited from two different clinics of KwaZulu-Natal province in South Africa. Vaginal specimens were collected using a Dacron swab and cultured in modified Diamonds medium. The minimum inhibitory concentrations (MICs) of T. vaginalis to metronidazole and tinidazole were determined in 94 positive clinical isolates using a micro-broth dilution method. Briefly trichomonads were added to Diamonds media containing two-fold dilutions (16 to 0.25 mg/L) of metronidazole or tinidazole and incubated anaerobically for 72 h. The lowest concentration at which no motile trichomonads were visualised under an inverted phase contrast microscope was considered the MIC. Propionibacterium acnes and Bacteroides fragilis were used as the resistant and sensitive controls respectively. MIC ≤ 1 mg/L was considered sensitive, MIC ≥4 mg/L was considered resistant; MIC between 1 mg/L and 4 mg/L was considered intermediate. The MIC of any isolate in the resistant range was repeated to confirm results.

Results Of the 94 isolates, 17 had an MIC ≥4 mg/L indicating in vitro resistance to metronidazole while 2 isolates had an MIC  ≥4 mg/L for tinidazole. Thirty-five and 33 isolates had an MIC of 2 mg/L (intermediate) for metronidazole and tinidazole respectively.

Conclusion High MIC of T. vaginalis to metronidazole is a public health concern however more research is needed to correlate in vitro resistance with clinical failure.

Disclosure of interest statement The authors have no conflict of interest to declare. No pharmaceutical grants were received in the development of this study.