Migration and spread of Bacillus cereus in mice with endophthalmitis and influence on inflammation / 中华微生物学和免疫学杂志

ABSTRACT

Objective:To investigate the causes of strong pathogenicity of Bacillus cereus ( B. cereus) in a mouse model of B. cereus endophthalmitis and the factors that might be related to the prognosis of the disease. Methods:C57BL/6J mice aged 6-8 weeks were injected with 1 μl PBS solution containing 100 CFU B. cereus into the vitreous cavity to construct traumatic endophthalmitis model, and a control group was set up by injecting the contralateral eyeball with 1 μl sterile PBS. A mouse model of Staphylococcus epidermidis ( S. epidermidis) endophthalmitis was constructed in the same way as disease control group. Real-time fluorescent quantitative polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA) were used to detect the levels of inflammatory cytokines at different time points. Histology, electroretinogram and transmission electron microscopy were used to detect the progression of endophthalmitis and retinal function at different time points. Results:B. cereus grew significantly faster than S. epidermidis in the eyes of C57BL/6 mice and gradually moved to the cornea 12 h after infection. The results of transmission electron microscopy showed that many more B. cereus were found in the iris with sparse pigment particles, while S. epidermidis could not be detected in the anterior segment after infection. The electroretinogram results showed that the amplitude of A wave and B wave of mice with B. cereus endophthalmitis decreased significantly 6 h after infection, and the B wave could not be detected 12 h after infection. Moreover, the amplitude reduction at different time points was significantly larger than that in the S. epidermidis endophthalmitis group. Histological examination found that compared with the S. epidermidis endophthalmitis group, the mice with B. cereus endophthalmitis had significantly increased inflammatory cells in the anterior chamber and vitreous cavity with a higher degree of infiltration, which was more destructive to the tissue structure. ELISA results showed that the activity of myeloperoxidase (MPO) was significantly stronger in the B. cereus endophthalmitis group than in the S. epidermidis endophthalmitis group, suggesting that a much more severe inflammation was induced. The expression of IL-6, TNF-α and IL-1β at the transcription and protein levels in the mouse model of B. cereus endophthalmitis were significantly higher than those in the mice with S. epidermidis endophthalmitis. Conclusions:B. cereus could induce severe endophthalmitis and tissue destruction in the eye due to its rapid growth and migration ability, which was an important factor leading to vision loss.