Drug Susceptibility of Trichomonas vaginalis to Metronidazole in Bushehr City (In Vitro)

Trichomoniasis is the most common non-viral sexually transmitted disease caused by the protozoan parasite Trichomonas vaginalis. Metronidazole (MTZ), a 5-nitroimidazole derivative, is the main antitrichomonal agent of choice for the treatment of trichomoniasis. Since 1962, some cases of treatment failure with metronidazole have been reported, and the increased resistance of the parasite to MTZ has emerged as a highly problematic public health issue. This study aimed to determine the current susceptibility of isolates of T. vaginalis to metronidazole in Bushehr city.

This study was performed on 20 T. vaginalis isolates collected from comprehensive health service centers and hospitals in Bushehr city. After the culture of the parasites, susceptibility testing was carried out using serial twofold dilutions of MTZ (2 to 64 μg/ml). The minimum inhibitory concentration (MIC) and the minimum lethal concentration (MLC) of the trichomonads were determined after 24 and 48 h of incubation at 36 °C. Drug susceptibility assays of all the isolates were carried out twice in triplicate under aerobic and anaerobic conditions.

One hundred percent of the T. vaginalis isolates (20/20) were susceptible to MTZ. Resistance to metronidazole was defined as aerobic MIC ≥50 μg/ml, which was not detected in any of the isolates. The mean aerobic MIC and MLC and the mean anaerobic MIC of the parasites were 3.8, 3.2 and 2.1 μg/ml, respectively.

The present study was the first to investigate drug susceptibility in T. vaginalis isolates in Bushehr city. Since no metronidazole-resistant isolates were found, the situation looked very promising. Nevertheless, the need for larger-scale research is inevitable in the province. Considering that most results are based on in vitro observations, conducting an in vivo study has also been recommended in recent years, as these studies could help develop real standards about clinical and microbiological responses to MTZ treatment.