The role of pili in Bacillus cereus intraocular infection

Abstract

Bacterial endophthalmitis is a potentially blinding intraocular infection. The bacterium Bacillus cereus causes a devastating form of this disease which progresses rapidly, resulting in significant inflammation and loss of vision within a few days. The outer surface of B. cereus incites the intraocular inflammatory response, likely through interactions with innate immune receptors such as TLRs. This study analyzed the role of B. cereus pili, adhesion appendages located on the bacterial surface, in experimental endophthalmitis. To test the hypothesis that the presence of pili contributed to intraocular inflammation and virulence, we analyzed the progress of experimental endophthalmitis in mouse eyes infected with wild type B. cereus (ATCC 14579) or its isogenic pilus-deficient mutant (ΔbcpA-srtD-bcpB or ΔPil). One hundred CFU were injected into the mid-vitreous of one eye of each mouse. Infections were analyzed by quantifying intraocular bacilli and retinal function loss, and by histology from 0 to 12 h postinfection. In vitro growth and hemolytic phenotypes of the infecting strains were also compared. There was no difference in hemolytic activity (1:8 titer), motility, or in vitro growth (p>0.05, every 2 h, 0-18 h) between wild type B. cereus and the ΔPil mutant. However, infected eyes contained greater numbers of wild type B. cereus than ΔPil during the infection course (p≤0.05, 3-12 h). Eyes infected with wild type B. cereus experienced greater losses in retinal function than eyes infected with the ΔPil mutant, but the differences were not always significant. Eyes infected with ΔPil or wild type B. cereus achieved similar degrees of severe inflammation. The results indicated that the intraocular growth of pilus-deficient B. cereus may have been better controlled, leading to a trend of greater retinal function in eyes infected with the pilus-deficient strain. Although this difference was not enough to significantly alter the severity of the inflammatory response, these results suggest a potential role for pili in protecting B. cereus from clearance during the early stages of endophthalmitis, which is a newly described virulence mechanism for this organism and this infection.

Expression of Bacillus cereus Virulence-Related Genes in an Ocular Infection-Related Environment

“…B. cereus ATCC 14,579 was studied as a prototype B. cereus species with a sequenced and annotated genome. This particular strain has also been well characterized in terms of its virulence and pathogenesis in endophthalmitis [9,16,19,22,23]. It has 13 rRNA loci, and rRNA constitutes the bulk of the total RNA.…”

Ocular Glands Become Infected Secondarily to Infectious Keratitis and Play a Role in Corneal Resistance to Infection

“…At the time of tissue harvest, mice were anesthetized and euthanized by cardiac perfusion with10 to 20 ml of PBS. After euthanasia, the numbers of P. aeruginosa CFU in eyes, HGs, and ELGs were quantified by track dilution on BHI agar, as described previously (48,49). Colonies were confirmed as Pseudomonas on Pseudomonas isolation agar (Sigma).…”

TheBacillusVirulome in Endophthalmitis

“…B. cereus ATCC 14579 was utilized in this studies since it represents a prototypical strain with a sequenced and annotated genome. The virulence and pathogenesis in endophthalmitis has been previously evaluated and established [9,16,[21][22][23].…”

“…Coburn et al -6 A thick peptidoglycan layer, capsular polysaccharide, lipotechoic and teichoic acids, lipoproteins, pili, a glycoprotein S-layer, and flagella comprise the B. cereus cell wall [13][14][15]. B. cereus pili interfered with bacterial clearance in a mouse model of endophthalmitis [16], suggesting a role as an antiphagoctyic factor. In the same model, a mutant strain of Bacillus deficient in the S-layer protein, SlpA, was less virulent relative to the wild type, parental strain [17].…”