[In vitro sensitivity of Entamoeba histolytica to metronidazole]

The chemotherapy of amebiasis includes different substances with intra and extraintestinal action. Nowadays, metronidazole is the election drug by its high efficacy and low toxicity. Some therapeutic failures with metronidazole in patients with invader amebiasis and some reports of resistance to it, of certain strains of Trichomonas vaginalis and species of Bacteroides have caused an increased interest to do new in vitro evaluation of this compound and to search of new antiamebic drugs. The object of this work was to standardize with our conditions a microtechnique to evaluate the sensibility to metronidazole, experimented by trophozoites of three amebic strains of different virulence (HK9:NIH, HM1:IMSS, HM3:IMSS) and to compare the effect exerted by the drug on them. We modified the technique proposed by Cedeño and Krogstad in 1983. First we read the results in a half of the time employed by them (24h) and after, we fixed the trophozoites with 0.25% glutaraldehyde before of make the counts of them. We compared the number of cells in microcultures of 3.2 x 10(4) trophozoites incubated during 24h with metronidazole (from 0.008 to 1 micrograms/ml) with the obtained in control microcultures. Each one of the strains showed to have a characteristic sensibility to the drug (p less than 0.001), which was directly proportional to the concentration. The middle effective dose of HK9 and HM1 strains was 0.3 microgram/ml and of 1 microgram/ml for HM3 strain. This technique seems to be reproducible and could be useful to quantify the in vitro activity of antiamebic agents.