Trichomonas vaginalis may be resistant to metronidazole therapy. The in vitro susceptibility of Trichomonas to metronidazole can be measured by the minimum lethal concentration (MLC).


Medium: Diamond's medium


Antibiotic: metronidazole


Antibiotic concentrations (serial dilutions of 200 µg/mL concentration):

(1) 0.75 µg/mL

(2) 1.5 µg/mL

(3) 3.1 µg/mL

(4) 6.2 µg/mL

(5) 12.5 µg/mL

(6) 25 µg/mL

(7) 50 µg/mL

(8) 100 µg/mL

(9) 200 µg/mL


Control: ATCC strain 30001 with MLC 0.5 µg/mL


The cultures are examined for motile trichomonads at 24 and 48 hours.



• The minimum lethal concentration is that with no motile trichomonads seen at 48 hours.

• The higher the MLC the more likely that oral metronidazole therapy will be ineffective.


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