The role of pili in Bacillus cereus intraocular infection.
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.
Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA; Dean A. McGee Eye Institute, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA. Electronic address: michelle-callegan@ouhsc.edu.
Michelle C
MC
Callegan
Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, 950 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA. Electronic address: Madhu-parkunan@ouhsc.edu.
Salai Madhumathi
SM
Parkunan
Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA. Electronic address: christopher-randall@ouhsc.edu.
C Blake
CB
Randall
Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA. Electronic address: phillip-coburn@ouhsc.edu.
Phillip S
PS
Coburn
Department of Cell Biology, University of Oklahoma Health Sciences Center, 950 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA. Electronic address: frederick-miller@ouhsc.edu.
Frederick C
FC
Miller
Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA. Electronic address: austin-lagrow@ouhsc.edu.
Austin L
AL
LaGrow
Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA. Electronic address: roger-astley@ouhsc.edu.
Roger A
RA
Astley
Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA. Electronic address: craig-land@ouhsc.edu.
Craig
C
Land
Department of Microbiology, University of Chicago, 920 East 58th Street, Chicago, IL, 60637, USA. Electronic address: soh@bsdad.uchicago.edu.
So-Young
SY
Oh
Department of Microbiology, University of Chicago, 920 East 58th Street, Chicago, IL, 60637, USA. Electronic address: oschnee@bsd.uchicago.edu.
Olaf
O
Schneewind
D000818:Animals; D001082:Aqueous Humor / Q000382:microbiology; D001409:Bacillus cereus / Q000472:pathogenicity*; D004195:Disease Models, Animal; D004596:Electroretinography; D009877:Endophthalmitis / Q000175:diagnosis / Q000382:microbiology*; D015818:Eye Infections, Bacterial / Q000175:diagnosis / Q000382:microbiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D012160:Retina / Q000382:microbiology / Q000473:pathology / Q000503:physiopathology
Bacillus; Endophthalmitis; Eye; Infection; Inflammation; Pili; Virulence