A rapid, high-throughput viability assay for Blastocystis spp. reveals metronidazole resistance and extensive subtype-dependent variations in drug susceptibilities.

Abstract

Blastocystis is an emerging protistan parasite of controversial pathogenesis. Although metronidazole (Mz) is standard therapy for Blastocystis infections, there have been accumulating reports of treatment failure, suggesting the existence of drug-resistant isolates. Furthermore, very little is known about Blastocystis susceptibility to standard antimicrobials. In the present study, we established resazurin and XTT viability microassays for Blastocystis spp. belonging to subtypes 4 and 7, both of which have been suggested to represent pathogenic zoonotic subtypes. The optimized resazurin assay was used to screen a total of 19 compounds against both subtypes. Interestingly, subtype 7 parasites were resistant to Mz, a 1-position-substituted 5-nitroimidazole (5-NI), while subtype 4 parasites were sensitive. Some cross-resistance was observed to tinidazole, another 1-position 5-NI. Conversely, subtype 4 parasites were resistant to emetine, while subtype 7 parasites were sensitive. Position 2 5-NIs were effective against both subtypes, as were ornidazole, nitazoxanide, furazolidone, mefloquine, quinicrine, quinine, cotrimoxazole (trimethoprim-sulfamethoxazole), and iodoacetamide. Both subtypes were resistant to chloroquine, doxycycline, paromomycin, ampicillin, and pyrimethamine. This is the first study to report extensive variations in drug sensitivities among two clinically important subtypes. Our study highlights the need to reevaluate established treatment regimens for Blastocystis infections and offers clear new treatment options for Mz treatment failures.

• Authors: Haris Mirza, Joshua D W Teo, Jacqui Upcroft, Kevin S W Tan
• Journal: Antimicrobial agents and chemotherapy (Antimicrob Agents Chemother) Vol. 55 Issue 2 Pg. 637-48 (Feb 2011) ISSN: 1098-6596 [Electronic] United States
• PMID: 21098237 (Publication Type: Evaluation Study, Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Antiprotozoal Agents
• Oxazines
• Tetrazolium Salts
• Xanthenes
• 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-((phenylamino)carbonyl)-2H-tetrazolium hydroxide
• Metronidazole
• resazurin
• Emetine

Topics

• Animals
• Antiprotozoal Agents (pharmacology)
• Blastocystis (classification, drug effects, growth & development)
• Blastocystis Infections (parasitology)
• Drug Resistance
• Emetine (pharmacology)
• High-Throughput Screening Assays (methods)
• Humans
• Metronidazole (pharmacology)
• Oxazines (metabolism)
• Oxidation-Reduction
• Parasitic Sensitivity Tests (methods)
• Reproducibility of Results
• Species Specificity
• Tetrazolium Salts (metabolism)
• Time Factors
• Xanthenes (metabolism)