Amebiasis is an intestinal disease transmitted by the protist parasite, Entamoeba histolytica. Lactobacillus acidophilus is a common inhabitant of healthy human gut and a probiotic that has antimicrobial properties against a number of pathogenic bacteria, fungi, and parasites. The aim of this study was to investigate the amebicide activity of L. acidophilus and its mechanisms. For this purpose, E. histolytica and L. acidophilus were co-incubated and the parasite’s viability was determined by eosin dye exclusion. The level of ozidized proteins (OXs) in the parasite was determined by resin-assisted capture RAC (OX–RAC). Incubation with L. acidophilus for two hours reduced the viability of E. histolytica trophozoites by 50%. As a result of the interaction with catalase, an enzyme that degrades hydrogen peroxide (H2O2) to water and oxygen, this amebicide activity is lost, indicating that it is mediated by H2O2 produced by L. acidophilus. Redox proteomics shows that L. acidophilus triggers the oxidation of many essential amebic enzymes such as pyruvate: ferredoxin oxidoreductase, the lectin Gal/GalNAc, and cysteine proteases (CPs). Further, trophozoites of E. histolytica incubated with L. acidophilus show reduced binding to mammalian cells. These results support L. acidophilus as a prophylactic candidate against amebiasis.

Queuosine (Q) is a naturally occurring modified nucleoside that occurs in the first position of transfer RNA anticodons such as Asp, Asn, His, and Tyr. As eukaryotes lack pathways to synthesize queuine, the Q nucleobase, they must obtain it from their diet or gut microbiota. Previously, we described the effects of queuine on the physiology of the eukaryotic parasite Entamoeba histolytica and characterized the enzyme EhTGT responsible for queuine incorporation into tRNA. At present, it is unknown how E. histolytica salvages queuine from gut bacteria. We used liquid chromatography–mass spectrometry (LC–MS) and N-acryloyl-3-aminophenylboronic acid (APB) PAGE analysis to demonstrate that E. histolytica trophozoites can salvage queuine from Q or E. coli K12 but not from the modified E. coli QueC strain, which cannot produce queuine. We then examined the role of EhDUF2419, a protein with homology to DNA glycosylase, as a queuine salvage enzyme in E. histolytica. We found that glutathione S-transferase (GST)-EhDUF2419 catalyzed the conversion of Q into queuine. Trophozoites silenced for EhDUF2419 expression are impaired in their ability to form Q-tRNA from Q or from E. coli. We also observed that Q or E. coli K12 partially protects control trophozoites from oxidative stress (OS), but not siEhDUF2419 trophozoites. Overall, our data reveal that EhDUF2419 is central for the direct salvaging of queuine from bacteria and for the resistance of the parasite to OS.

Amoebiasis is an intestinal disease transmitted by the protist parasite, Entamoeba histolytica, following the ingestion of contaminated food and water. In the colon, E. histolytica can phagocytose bacteria that are the main components of the microbial flora. Most infected individuals are asymptomatic but for unknown reasons, the parasite can become virulent and invasive, causes amebic dysentery, and migrates to the liver, where they cause hepatocellular damage. For the last few decades, it has become evident that E. histolytica virulence is directly linked to its interaction with the gut microbiota. Lactobacillus acidophilus is a common inhabitant of healthy human gut and a probiotic that present antimicrobial activity against many pathogenic bacteria, fungi and parasites. The purpose of this study was to examine the mechanisms behind the innate amebicide activity of L.acidophilus. We found that this activity is mediated by hydrogen peroxide (H2O2) produced by L. acidophilus. Redox proteomics shows that L. acidophilus triggers the oxidation of many essential amebic enzymes like pyruvate:ferredoxin oxidoreductase, the lectin Gal/GalNAc and cysteine proteases (CPs). Further, trophozoites of E.histolytica cultivated with L.acidophilus show reduced binding to mammalian cells. These results support L.acidophilus as a prophylactic candidate against amoebiasis.

Amebiasis is an intestinal disease transmitted by the protist parasite, Entamoeba histolytica. Lactobacillus acidophilus is a common inhabitant of healthy human gut and a probiotic that has antimicrobial properties against a number of pathogenic bacteria, fungi, and parasites. The aim of this study was to investigate the amebicide activity of L. acidophilus and its mechanisms. For this purpose E.histolytica and L.acidophilus were co-incubated and the parasite’s viability was determined by eosin dye exclusion. The level of ozidized proteins (OXs) in the parasite was determined by resin-assisted capture RAC (OX-RAC). Incubation with L.acidophilus for two hours reduced the viability of E.histolytica trophozoites by 50%. As a result of the interaction with catalase, an enzyme that degrades hydrogen peroxide (H2O2) to water and oxygen, this amebicide activity is lost, indicating that it is mediated by H2O2 produced by L.acidophilus. Redox proteomics shows that L. acidophilus triggers the oxidation of many essential amebic enzymes like pyruvate:ferredoxin oxidoreductase, the lectin Gal/GalNAc and cysteine proteases (CPs). Further, trophozoites of E.histolytica incubated with L.acidophilus show reduced binding to mammalian cells. These results support L.acidophilus as a prophylactic candidate against amebiasis.