Abstract
Bacillus cereus produces many factors linked to pathogenesis and is recognized for causing gastrointestinal toxemia and infections. B. cereus also causes a fulminant and often blinding intraocular infection called endophthalmitis. We reported that the PlcR/PapR system regulates intraocular virulence, but the specific factors that contribute to B. cereus virulence in the eye remain elusive. Here, we compared gene expression in ex vivo vitreous humor with expression in Luria Bertani (LB) and Brain Heart Infusion (BHI) broth by RNA-Seq. The expression of several cytolytic toxins in vitreous was less than or similar to levels observed in BHI or LB. Regulators of virulence genes, including PlcR/PapR, were expressed in vitreous. PlcR/PapR was expressed at low levels, though we reported that PlcR-deficient B. cereus was attenuated in the eye. Chemotaxis and motility genes were expressed at similar levels in LB and BHI, but at low to undetectable levels in vitreous, although motility is an important phenotype for B. cereus in the eye. Superoxide dismutase, a potential inhibitor of neutrophil activity in the eye during infection, was the most highly expressed gene in vitreous. Genes previously reported to be important to intraocular virulence were expressed at low levels in vitreous under these conditions, possibly because in vivo cues are required for higher level expression. Genes expressed in vitreous may contribute to the unique virulence of B. cereus endophthalmitis, and future analysis of the B. cereus virulome in the eye will identify those expressed in vivo, which could potentially be targeted to arrest virulence.
Highlights
B. cereus is one of the leading causes of bacterial gastrointestinal infections and produces a variety of toxins that contribute to the pathogenesis of these infections
Our results suggested that the B. cereus superoxide dismutase might represent a target for therapeutic intervention, and demonstrated that virulence-related genes are expressed in ex vivo vitreous during the stationary phase of growth, which may relate to expression in later stages of infection
In vitro growth of B. cereus ATCC 14,579 in the three environments was compared to assess whether differences in growth might impact the results of the RNA-Seq experiments
Summary
B. cereus is one of the leading causes of bacterial gastrointestinal infections and produces a variety of toxins that contribute to the pathogenesis of these infections. We evaluated the expression levels of a subset of factors involved in virulence and its transcriptional regulation, motility, and chemotaxis after growth to stationary phase in an ocular infection-related environment ex vivo. This late stage correlates with a stage of infection when significant inflammation and retinal function loss have occurred. Our results suggested that the B. cereus superoxide dismutase might represent a target for therapeutic intervention, and demonstrated that virulence-related genes are expressed in ex vivo vitreous during the stationary phase of growth, which may relate to expression in later stages of infection. These results provided the framework for studying the B. cereus virulome during ocular infections in order to identify virulence-related genes expressed in vivo and suggest possible candidate genes that could be potentially targeted to mitigate virulence
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