Phenotypic and transcriptional profiling in Entamoeba histolytica reveal costs to fitness and adaptive responses associated with metronidazole resistance

In vitro studies have described metronidazole (MTZ) resistance and the potential mechanisms involved. Costs to fitness and adaptive responses associated with resistance, however, have not been investigated. In this study we generated an HM-1-derived strain resistant to 12 µM MTZ (MTZR). We examined its phenotypic and transcriptional profile to determine the consequences and mRNA level changes associated with MTZ resistance. The expression profile of 9,230 genes in wild-type and metronidazole-resistant strains was compared. Transcriptome analysis revealed 142 differentially expressed genes in MTZR. In contrast to other MTZ-resistant parasites, MTZR did not down-regulate pyruvate:ferredoxin oxidoreductase, but showed increased expression of genes for a hypothetical protein (HP1) and several iron-sulfur flavoproteins, and the downregulation of genes for leucin-rich proteins. Overexpression of HP1-HA did not confer MTZR level of resistance, but provided a slight advantage in cell survival. Fisher's exact test showed 24 significantly enriched GO terms in MTZR, and a 3-way comparison of modulated genes with MTZR cultured without MTZ and HM-1 cultured with MTZ showed that 88 genes were specific to MTZR. Wild-type and the MTZ-resistant strain MTZR were cultured either in the presence or absence of MTZ. 2 biological replicates per strain/condition.