**1. Introduction**

Amebiasis is an enormous global medical problem because of poor sanitary conditions and unsafe hygiene practices existing in many parts of the world. According to the World Health Organization, 50 million people in India, Southeast Asia, Africa, and Latin America suffer from amebic dysentery and amebiasis causes the death of at least 100,000 individuals each year. The main mode of transmission for amebiasis is the ingestion of food or water that is contaminated with feces containing *E. histolytica* cysts. After the cyst form has been swallowed by the host, excystation occurs in the intestinal lumen, followed by colonization of the large intestine by the trophozoites where they continue to divide and encyst. Eventually, both trophozoites and cysts are excreted in stools. Only 10% of the infected individuals will develop acute intestinal and extra-intestinal diseases. One possible explanation for this observation is the difference in the gut microbiota between individuals who may significantly influence the host's immune response in amebiasis and *E. histolytica*'s virulence [1]. Over the last few decades, it has become evident that *E. histolytica*'s pathogenicity is directly linked to the parasite's interaction with the gut microbiota [2], as the parasites are reported to feed on bacteria and cellular debris found in the large intestine [1]. However, such feeding is very selective, where only those bacteria with the appropriate recognition molecules are ingested by the parasite [3]. Amebiasis is characterized by acute inflammation of the intestine with release of pro-inflammatory

**Citation:** Sarid, L.; Zanditenas, E.; Ye, J.; Trebicz-Geffen, M.; Ankri, S. Insights into the Mechanisms of *Lactobacillus acidophilus* Activity against *Entamoeba histolytica* by Using Thiol Redox Proteomics. *Antioxidants* **2022**, *11*, 814. https://doi.org/ 10.3390/antiox11050814

Academic Editor: Simone Carradori

Received: 10 March 2022 Accepted: 20 April 2022 Published: 22 April 2022

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cytokines, reactive oxygen species (ROS), and reactive nitrogen species (RNS) from activated cells of the host's immune system. ROS and RNS are the major cytotoxic effectors for killing *E. histolytica* and cause oxidation and nitrosylation of amebic proteins, trigger stress responses, and inhibit glycolysis and the activity of some virulence factors [4–7]. Cellular means of subverting the toxicity of oxidative stress (OS) are important for the success of infectious diseases. No vaccine against amebiasis currently exists; the drug of choice for treating amebiasis is metronidazole, which may cause severe side effects such as nausea, vomiting, headaches, a metallic or bitter taste in the mouth, and more serious effects such as anorexia, ataxia, and skin rashes/itching [8,9]. Additionally, some clinical strains of *E. histolytica* are less sensitive to metronidazole, suggesting the emergence of metronidazole-resistant strains [10,11].

Probiotics are live organisms which, when administered in adequate amounts, confer a health benefit to the host [12,13]. Probiotics and commensal bacteria have been suggested to have some influence on the outcome of protozoan infections [14–16]. As an alternative bio-therapeutic for amebiasis, there are a number of studies which have been conducted, interestingly most of these studies are aimed at the efficiency of the probiotic at inhibiting adhesion of the protozoa to the intestinal mucosal surface [17,18]. Recently we have shown that *Lactobacillus acidophilus* is detrimental to *E. histolytica* [19]. This detrimental effect is associated with the transcription by the parasite of genes encoding major signaling molecules, such as kinases, regulators of small GTPases and oxidoreductases and genes encoding proteins necessary for ribosome structure. It has been suggested that the probiotic effect of certain bacteria (such as *L. acidophilus*) is mediated by the ability to produce H2O2 [20] via an NADH-dependent flavin reductase [21] and to maintain a normal, homeostatic microbiota [21]. In this study, we demonstrated that H2O2 produced by *L. acidophilus* caused the death of the parasite by oxidizing important amebic proteins. To our knowledge, this work provides the first comprehensive analysis of OXs in a protozoan parasite exposed to *L. acidophilus*.
