The interaction between flagellin and the glycosphingolipid Gb3 on host cells contributes to <i>Bacillus cereus</i> acute infection

<b>Bacillus cereus</b> is an opportunistic pathogen that can cause emetic or diarrheal foodborne illness. Previous studies have identified multiple pathogenic <i>B. cereus</i> strains and characterized a variety of virulence factors. Here, we demonstrate that the virulence and lethality of <i>B. cereus</i> for mammalian cells and host animals involve the interaction of <i>B. cereus</i> flagellin proteins and the host-cell-surface-localized glycosphingolipid Gb3 (CD77, Galα1-4Galβ1-4Glcβ1-Cer). We initially found that <i>B. cereus</i> infection was less lethal for Gb3-deficiencient <i>A4galt</i>^−/- mice than for wild-type mice. Subsequent experiments established that some factor other than secreted toxins must account of the observed differential lethality: Gb3-deficiencient <i>A4galt</i>^−/- mice were equally susceptible to secreted-virulence-factor-mediated death as WT mice, and we observed no differences in the bacterial loads of spleens or livers of mice treated with <i>B. cereus</i> strain vs. mice infected with a mutant variant of incapable of producing many secreted toxins. A screen for host-interacting <i>B. cereus</i> cell wall components identified the well-known flagellin protein, and both flagellin knockout strain assays and Gb3 inhibitor studies confirmed that flagellin does interact with Gb3 in a manner that affects <i>B. cereus</i> infection of host cells. Finally, we show that treatment with polyclonal antibody against flagellin can protect mice against <i>B. cereus</i> infection. Thus, beyond demonstrating a previously unappreciated interaction between a bacterial motor protein and a mammalian cell wall glycosphingolipid, our study will provide useful information for the development of therapies to treat infection of <i>B. cereus</i>.