Digestive exophagy of biofilms by intestinal amoeba and its impact on stress tolerance and cytotoxicity

Abstract

The human protozoan parasite Entamoeba histolytica is responsible for amebiasis, a disease endemic to developing countries. E. histolytica trophozoites colonize the large intestine, primarily feeding on bacteria. However, in the gastrointestinal tract, bacterial cells form aggregates or structured communities called biofilms too large for phagocytosis. Remarkably, trophozoites are still able to invade and degrade established biofilms, utilizing a mechanism that mimics digestive exophagy. Digestive exophagy refers to the secretion of digestive enzymes that promote the digestion of objects too large for direct phagocytosis by phagocytes. E. histolytica cysteine proteinases (CPs) play a crucial role in the degradation process of Bacillus subtilis biofilm. These proteinases target TasA, a major component of the B. subtilis biofilm matrix, also contributing to the adhesion of the parasite to the biofilm. In addition, they are also involved in the degradation of biofilms formed by Gram-negative and Gram-positive enteric pathogens. Furthermore, biofilms also play an important role in protecting trophozoites against oxidative stress. This specific mechanism suggests that the amoeba has adapted to prey on biofilms, potentially serving as an untapped reservoir for novel therapeutic approaches to treat biofilms. Consistently, products derived from the amoeba have been shown to restore antibiotic sensitivity to biofilm cells. In addition, our findings reveal that probiotic biofilms can act as a protective shield for mammalian cells, hindering the progression of the parasite towards them.

Unraveling the interplay between unicellular parasites and bacterial biofilms: Implications for disease persistence and antibiotic resistance

“…These proteases are found in Acanthamoeba spp [ 32 , 33 ]. and have been identified as essential for degrading biofilms in E. histolytica through the degradation of extracellular proteinous matrix components, such as TasA in B. subtilis biofilm [ 34 ]. Interestingly, these CPs have been recognized both in Acanthamoeba [ 33 ] and in E.histolytica [ 35–37 ] as central virulence factors involved in tissue invasion.…”

“…These proteins can be involved in the synthesis and modification of the extracellular matrix, as well as in the regulation of biofilm development and behaviour. As previously stated, CPs produced by E. histolytica play a crucial role in breaking down biofilms formed by B. subtilis and E. coli [ 34 ]. While the degradation of TasA by E. histolytica CPs explains the mechanism behind B. subtilis biofilm degradation, the situation is different for E. coli curli.…”

“…While the degradation of TasA by E. histolytica CPs explains the mechanism behind B. subtilis biofilm degradation, the situation is different for E. coli curli. Curli, the primary proteinaceous component of enteric biofilms, is resistant to degradation by these CPs [ 34 ]. This raises questions about which specific component of the E. coli biofilm is targeted by E.histolytica CPs.…”

“…The interaction between trophozoites and biofilm has additional notable implications, especially regarding biofilm antibiotic tolerance. For instance, E. histolytica CPs enhance the sensitivity of the biofilm to antimicrobial agents such as sodium hypochlorite and ampicillin by damaging the biofilm matrix [ 34 ].…”

“…These protective properties can be conferred to parasites leaving inside biofilms. For instance, E. histolytica is shielded against oxidative stress (OS) when it resides inside a B. subtilis biofilm [ 34 ]. While the protective mechanism is thought to be related to the presence of an oxygen gradient within the biofilm [ 40 , 41 ], it’s also plausible that certain antioxidant molecules produced by the biofilm, such as Pulcherrimin, an iron-binding reddish pigment [ 91 ], could contribute to this protective effect.…”