In vitro susceptibilities of 25 Giardia lamblia isolates of human origin to six commonly used antiprotozoal agents

Abstract

The role drug resistance plays in the occurrence of chronic and recurrent giardiasis has not been established. Extensive data on the susceptibility to antimicrobial agents of living Giardia spp. trophozoites from human origin are lacking. We have determined with a macrodilution method in semisolid medium the in vitro susceptibility of 25 Giardia lamblia isolates, all obtained by routine cultivation of the duodenal fluid of children to six commonly used antiprotozoal drugs. The results showed tinidazole to be the most active drug (all isolates have MICs of .0.5 ,ug/ml). Metronidazole was equally active on all but one isolate, for which an MIC between 0.5 and 1 ,ig/ml was found. Furazolidone was the most active nonimidazole compound tested. More than 50% of the isolates were very susceptible to paromomycin, pyrimethamine, and chloroquine. Two of the strains presented an MIC for paromomycin higher than 10 ,Lg/ml, and six strains needed more than 50 ,ug of pyrimethamine per ml to be inhibited. Decreased susceptibility of several of the isolates to different agents appears to be linked.Although susceptibility testing is not the principal problem in Giardia spp. research, it is not known whether drug resistance or drug ineffectiveness plays a role in chronic and recurrent giardiasis. This is mainly due to the fact that no easy technique was available for in vitro cultivation of the microorganism.Earlier described studies on the susceptibility of Giardia spp. to antimicrobial agents were technically very instructive (2, 4, 6, 11), but interpretation of the data was difficult; the number of strains tested was low (2, 4, 6, 11), and the isolates were mostly not of human origin (4, 6, 11). Moreover, the organisms were often maintained for a long time in axenic cultures before testing. This may have caused changes in important factors like generation time.Recently, we developed a technique enabling the routine cultivation of Giardia lamblia trophozoites from human duodenal aspirates (5). By determining systematically the in vitro susceptibility of these isolates with a macrodilution method in semisolid medium (4) (3,5) and dispensed in 16-mi screw-capped glass tubes. Once the cultures were fully grown, the tubes were placed in ice water for 5 min to detach the microorganisms from the glass, centrifuged, and suspended in 2 ml of phosphate-buffered saline. A trophozoit count was performed in a FuchsRosenthal chamber, and the suspension was adjusted to a final concentration of 3 x 106 trophozoites per ml.Antimicrobial agents.The following antiprotozoal drugs were tested: tinidazole (Fasigyn; Roerig), metronidazole (Flagyl; Rhone-Poulenc), chloroquine (Nivaquine; RhonePoulenc), pyrimethamine (Daraprim; Wellcome Research Laboratories), furazolidone (Furoxone; Norwich), and paromomycin (Hematin; Parke, Davis & Co.). Fresh stock solutions of 2,000 ,ug/ml were prepared by dissolving pure substance of each test drug in 3 ml of distilled water (for chloroquine and paromomycin) or dimethyl formamide (for tinidazole, metronidazole, py...

The efficacy of chloroquine treatment against naturally occuring Giardia duodenalis infection in lambs

“…Esto se explica brevemente con estudios anteriores. Se ha detectado que la Cq tiene actividad antigiardial in-vitro (22,23). Gordts et al (22) ensayaron con 25 aislamientos de Giardia y declararon que más de la mitad de los aislamientos de Giardia fueron muy susceptibles a la Cq in-vitro.…”

“…Se ha detectado que la Cq tiene actividad antigiardial in-vitro (22,23). Gordts et al (22) ensayaron con 25 aislamientos de Giardia y declararon que más de la mitad de los aislamientos de Giardia fueron muy susceptibles a la Cq in-vitro. Del mismo modo Baveja et al (23) sugieren la eficacia de la Cq en la reducción de la capacidad in-vitro de la Giardia para fijarse y colonizar.…”

Treatment of Giardiasis

“…Of the nitroimidazoles, tinidazole and metronidazole have consistently demonstrated the greatest in vitro activity; tinidazole possesses a slight advantage (30,32,55,101). More highly substituted nitroimidazoles, such as miconazole, clotrimazole, itraconazole, and ketoconazole, were developed for their antifungal activity and are not effective agents against G. lamblia (55).…”

In-vitro susceptibility of Giardia lamblia to albendazole, mebendazole and other chemotherapeutic agents

“…Other drugs were obtained in Mexico City from the manufacturers or their subsidiaries : albendazole and nifuroxazide from SmithKline-Beecham, mebendazole from Janssen, etofamide from Carlo Erba-Farmitalia, quinfamide and nalidixic acid from Winthrop, hemezole from Silanes, ornidazole from Roche, and secnidazole from Rh6ne Poulenc. Metronidazole, tinidazole, mepacrine and ornidazole were dissolved in water, hemezole and nalidixic acid were dissolved in sodium bicarbonate solution (pH 7.2); other compounds were dissolved in dime th yl formamide .…”