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.

Bacillus cereus is recognized as a causative agent of gastrointestinal syndromes, but can also cause a devastating form of intraocular infection known as endophthalmitis. We have previously reported that the PlcR/PapR master virulence factor regulator system regulates intraocular virulence, and that the S-layer protein (SlpA) contributes to the severity of B. cereus endophthalmitis. To better understand the role of other B. cereus virulence genes in endophthalmitis, expression of a subset of factors was measured at the midpoint of disease progression in a murine model of endophthalmitis by RNA-Seq. Several cytolytic toxins were expressed at significantly higher levels in vivo than in BHI. The virulence regulators codY, gntR, and nprR were also expressed in vivo. However, at this timepoint, plcR/papR was not detectable, although we previously reported that a B. cereus mutant deficient in PlcR was attenuated in the eye. The motility-related genes fla, fliF, and motB, and the chemotaxis-related gene cheA were detected during infection. We have shown previously that motility and chemotaxis phenotypes are important in B. cereus endophthalmitis. The sodA2 variant of manganese superoxide dismutase was the most highly expressed gene in vivo. Expression of the surface layer protein gene, slpA, an activator of Toll-like receptors (TLR)−2 and −4, was also detected during infection, albeit at low levels. Genes expressed in a mouse model of Bacillus endophthalmitis might play crucial roles in the unique virulence of B. cereus endophthalmitis, and serve as candidates for novel therapies designed to attenuate the severity of this often blinding infection.

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 had 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. Impact statement: B. cereus is the causative agent of gastrointestinal infections, but can also cause a serious infection of the eye that often results in blindness or enucleation. Current therapeutic measures often fail to mitigate these poor outcomes. This necessitates the development of new treatment modalities based on new targets. To begin to better define those B. cereus factors with roles in intraocular infection, we analyzed the expression of genes related to gastrointestinal infections, as well as those with both known and hypothesized roles in intraocular infections, after growth in an ex vivo vitreous. Potentially targetable candidate genes were demonstrated to be expressed in vitreous, which suggests that these genes might contribute to the unique virulence of B. cereus endophthalmitis. Importantly, our results lay the groundwork for assessing the expression of these genes in vivo and defining the virulome of B. cereus in intraocular infections.

Background. Capnocytophaga canimorsus is a fastidious, slow-growing, Gram-negative rod that is a commensal bacterium in normal gingival flora of canine and feline species. Infection with the organism may cause disease ranging from flu-like symptoms to disseminated intravascular coagulation (DIC), fulminant sepsis, meningitis, and endocarditis with an overall fatality rate of 6-26%. Risk factors for infection from C. canimorsus include immunosuppression, alcoholism, and asplenia. Case Presentation. We describe an unusual case with a relatively indolent clinical course and an urticarial exanthem in an otherwise young immunocompetent patient with a history of type 1 diabetes. The patient presented to the Emergency Department (ED) with a <1-day history of rhinorrhea, fever, and dyspnea. He met sepsis criteria on initial presentation, but left against medical advice and returned to the ED the following day, with new arthralgias and a diffuse rash, multiple erythematous, tender macules scattered across his trunk and extremities, and tonsillar erythema. He had not taken the doses of the prescribed amoxicillin. Blood cultures two days later signaled positive for growth with the Gram stain showing a Gram-negative rod. Three 7-8 cm tender targetoid lesions with central clearing were identified on the patient's back. The patient reported two nonengorged ticks crawling on his body a week prior and sustaining a dog bite to his ear three weeks before presentation. Ultimately, the organism was identified as C. canimorsus through MALDI-TOF mass spectrometry and additional biochemical testing. He was given appropriate antibiotics and improved clinically thereafter. Despite the patient's bacteremia, he never progressed to fulminant sepsis and followed a mild clinical course with several unusual characteristics. C. canimorsus is an uncommon cause of illness in humans, but is an important pathogen to consider when evaluating a patient with a dog bite, known risk factors, and an urticarial exanthem as empiric treatment may prevent severe outcomes.

Bacillus cereus is recognized as a causative agent of gastrointestinal syndromes, but can also cause a devastating form of intraocular infection known as endophthalmitis. We have previously reported that the PlcR/PapR master virulence factor regulator system regulates intraocular virulence, and that the S-layer protein (SlpA) contributes to the severity of B. cereus endophthalmitis. To begin to better understand the role of other B. cereus virulence genes in endophthalmitis, expression levels of a subset of factors was measured at the midpoint of disease progression in a murine model of experimental endophthalmitis by RNA-Seq. Several cytolytic toxins were expressed at significantly higher levels in vivo than in BHI. The virulence regulators codY, gntR, and nprR were also expressed in vivo. However, at this timepoint, plcR/papR was not detectable, we previously reported that a B. cereus mutant deficient in PlcR was attenuated in the eye. The motility-related genes fla, fliF, and motB, and the chemotaxis-related gene cheA were detected during infection. We have shown previously that motility and chemotaxis phenotypes are important in B. cereus endophthalmitis. The sodA2 variant of manganese superoxide dismutase was the most highly expression gene in vivo , suggesting that this gene is criticial for intraocular survival, potentially through inhibition of neutrophil activity. Expression of the surface layer protein gene, slpA, an activator of Toll-like receptors (TLR) −2 and −4, and a potent contributor to intraocular inflammation and disease severvity, was also detected during infection, albeit at low levels. In summary, genes expressed in a mouse model of Bacillus endophthalmitis might prove to play crucial roles in the unique virulence of B. cereus endophthalmitis, and serve as candidates for novel therapies designed attenuate the severity of this often blinding infection. Impact statement: B. cereus causes a potent and rapid infection of the eye that usually results in blindness or enucleation, even with the utilization of current treatment modalities. This necessitates the development of new treatment modalities based on new targets. To begin to better define those B. cereus factors with roles in intraocular infection, we analyzed the expression of genes with both known and hypothesized roles in intraocular infection at the midpoint of infection using a murine model of Bacillus endophthalmitis. Potentially targetable candidate genes were demonstrated to be expressed in vivo , which suggests that these genes might contribute to the unique virulence of B. cereus endophthalmitis. Importantly, our results begin to define the virulome of B. cereus in intraocular infections and identify previously uncharacterized factors with potential roles in the severity and outcome of Bacillus endophthalmitis.