Disassembly of F-Actin Cytoskeleton after Interaction of Bacillus cereus with Fully Differentiated Human Intestinal Caco-2 Cells

Abstract

In the present study, the role of direct procaryote-eucaryote interactions in the virulence of Bacillus cereus was investigated. As a model of human enterocytes, differentiated Caco-2 cells were used. Infection of fully differentiated Caco-2 cells with B. cereus in the exponential phase of growth, in order to minimize the concentration of spores or sporulating microorganisms, shows that a strain-dependent cytopathic effect develops. Interestingly, addition of 3-h-old cultures of some strains resulted in complete detachment of the cultured cells after a 3-h infection whereas no such effect was found after a 3-h infection with 16-h-old cultures. Infection of enterocyte-like cells with B. cereus leads to disruption of the F-actin network and necrosis. Even though the effect of secreted factors cannot be ruled out, direct eucaryote-procaryote interaction seems to be necessary. In addition, we observed that some B. cereus strains were able to be internalized in Caco-2 cells. Our findings add a new insight into the mechanisms of virulence of B. cereus in the context of intestinal infection.Bacillus cereus is a spore-forming microorganism responsible for different pathological processes. In the context of intestinal infections, this microorganism is associated with emetic and diarrheic syndromes, and its role in extraintestinal infections has been also reported (14,15). So far, the virulence of B. cereus has been ascribed to the production of exocellular factors such as (i) cereolysin O, a thiol-activated cholesterol binding cytolysin (3, 25); (ii) phospholipases (8, 10, 23); (iii) emetic toxin (cereulide), a heat-stable cyclic dodecadepsipeptide with a molecular mass of around 1.2 kDa (1, 2, 37); (iv) hemolysin BL, a tripartite enterotoxin that requires all the three components (B, L1, and L2) for maximal activity (5,7,8,9,10,15,35); (v) the nonhemolytic enterotoxin complex, a complex of three subunits (34); (vi) hemolysin IV (Hly-IV), which has a strong effect on plasma membranes with a wide range of compositions (8); and (vii) the cytotoxic protein CytK, associated with necrotic enteritis (26,34).A cellular response triggered by the interaction between microorganisms and intestinal epithelial cells contributes to the virulence of several pathogens. These biological effects are related to the binding of bacterial surface structures and/or bacterial toxins to cell receptors coupled with cellular signaling pathways. Attack of the host cell cytoskeleton is the main mechanism by which pathogenic microorganisms structurally and functionally alter the host cells, particularly the intestinal epithelial barrier. This interference with the organization of the cytoskeleton can be mediated by enzymatic modification by soluble toxins (12) or by upregulation of depolimerization cascades by direct prokaryote-eucaryote interactions (11,24,39). The ability of microorganisms of the genus Bacillus to interact with Caco-2 and HeLa cells has been reported, but no further insight into the role of this interaction in the virulence of this...

Bacillus cereusInduces Permeability of an In Vitro Blood-Retina Barrier

“…B. cereus has also been shown to induce cytotoxicity in HeLa cells (50) and necrosis of human Caco-2 enterocytes (39). In these Caco-2 enterocytes, the loss of F-actin after infection with B. cereus was consistent with epithelial cell necrosis (39). Likewise, unpublished studies in our laboratory indicated that Bacillus induced degradation of F-actin and condensation of tubulin around the nucleus.…”

A case of intoxication due to a highly cytotoxic Bacillus cereus strain isolated from cooked chicken

“…To evaluate association (adhering plus invading bacteria), monolayers were exhaustively washed with PBS and incubated with 1 ml distilled water per well to lyse eukaryotic cells. Serial France) and incubated at 37 °C for 16 h. Invasion was assessed by the aminoglycoside protection assay as previously reported (Minnaard et al, 2004). All the infection assays were performed in DMEM FCS-free.…”

Aerobic bacterial microbiota of the conjunctiva in diabetic patients with normal and altered glycated hemoglobin levels in two regions in Brazil

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