**2. Materials and Methods**

#### *2.1. E. histolytica and L. acidophilus Culture*

*E. histolytica* trophozoites, the HM-1:IMSS strain (a gift from Samudrala Gourinath, Jawaharlal Nehru University, New Delhi, India), were grown and harvested according to a previously reported protocol [22].

*L. acidophilus* ATCC4356 strain was cultivated in De Man, Rogosa and Sharpe (MRS) media (Sigma-Aldrich, Jerusalem, Israel) overnight at 37 ◦C with agitation (200 rpm) on a New Brunswick Innova 4300 Incubator Shaker (Marshall Scientific, Hampton, NH, USA). Heat-killed *L. acidophilus* was cultivated in MRS media (Sigma-Aldrich, Jerusalem, Israel) overnight at 37 ◦C with agitation, followed by autoclaving at 121 ◦C and 1.05 kg/cm<sup>2</sup> for 15 min.

#### *2.2. Reagents*

Catalase from bovine liver (C9322) was purchased from Sigma-Aldrich (Jerusalem, Israel).

#### *2.3. Ferrous Oxidation-Xylenol Orange (FOX) Assay*

The amount of H2O2 produced by *L. acidophilus* was determined by the FOX assay according to a previously reported protocol [23].
