Abstract
B. cereus possesses flagella which allow the organism to migrate within the eye during a blinding form of intraocular infection called endophthalmitis. Because flagella is a ligand for Toll-like receptor 5 (TLR5), we hypothesized that TLR5 contributed to endophthalmitis pathogenesis. Endophthalmitis was induced in C57BL/6J and TLR5−/− mice by injecting 100 CFU of B. cereus into the mid-vitreous. Eyes were analyzed for intraocular bacterial growth, retinal function, and inflammation by published methods. Purified B. cereus flagellin was also injected into the mid-vitreous of wild type C57BL/6J mice and inflammation was analyzed. TLR5 activation by B. cereus flagellin was also analyzed in vitro. B. cereus grew rapidly and at similar rates in infected eyes of C57BL/6J and TLR5−/− mice. A significant loss in retinal function in both groups of mice was observed at 8 and 12 hours postinfection. Retinal architecture disruption and acute inflammation (neutrophil infiltration and proinflammatory cytokine concentrations) increased and were significant at 8 and 12 hours postinfection. Acute inflammation was comparable in TLR5−/− and C57BL/6J mice. Physiological concentrations of purified B. cereus flagellin caused significant inflammation in C57BL/6J mouse eyes, but not to the extent of that observed during active infection. Purified B. cereus flagellin was a weak agonist for TLR5 in vitro. These results demonstrated that the absence of TLR5 did not have a significant effect on the evolution of B. cereus endophthalmitis. This disparity may be due to sequence differences in important TLR5 binding domains in B. cereus flagellin or the lack of flagellin monomers in the eye to activate TLR5 during infection. Taken together, these results suggest a limited role for flagellin/TLR5 interactions in B. cereus endophthalmitis. Based on this and previous data, the importance of flagella in this disease lies in its contribution to the motility of the organism within the eye during infection.
Highlights
B. cereus is a Gram-positive, sporulating bacterium that is more commonly recognized for causing food-borne illnesses, chronic skin infections, and systemic diseases such as meningitis and pneumonia [1]
Sequence Analysis Flagellin sequences for B. cereus (NP_831435.1), B. anthracis (WP_001222388.1), B. thuringiensis (ABD33778.1), and S. enterica serovar typhimurium (S07276) were aligned, displayed, and analyzed with ClustalW (European Bioinformatics Institute, Cambridgeshire UK) [41]
We sought to determine the role of Toll-like receptor 5 (TLR5) in endophthalmitis caused by B. cereus, an organism which possesses the TLR5 ligand, flagella
Summary
B. cereus is a Gram-positive, sporulating bacterium that is more commonly recognized for causing food-borne illnesses, chronic skin infections, and systemic diseases such as meningitis and pneumonia [1]. Nosocomial infection pseudo-outbreaks caused by B. cereus have been reported in the last decade and have been attributed to contaminated disinfecting agents like ethyl alcohol [2] and alcohol swabs [3], or contaminated equipment like airflow sensors, intravenous catheters [1,4], and ventilator and filtration units [1,5,6]. B. cereus is highly associated with a blinding ocular infection termed endophthalmitis. While cases of postoperative endophthalmitis generally respond positively to treatment, cases of post-traumatic and endogenous endophthalmitis caused by B. cereus have a significantly greater failure rate, necessitating the search for better strategies to combat the disease
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