Michelle C. Callegan, PhD


Ph.D. :
1995, Louisiana State University

Research Interests: Molecular Pathogenesis of Bacterial Ocular Infections

Email: Michelle-Callegan@ouhsc.edu
Lab Website: http://calleganlab.org

Dr. Callegan

Research Emphasis

Bacillus cereus is an insidious ocular pathogen, causing a rapid and fulminant endophthalmitis that invariably leads to blindness within one to two days. Despite aggressive antibiotic and surgical intervention, B. cereus endophthalmitis has a relatively poor prognosis. There is presently no universal therapeutic regimen for successful treatment of Bacillus and other forms of severe bacterial endophthalmitis. Clinicians and researchers have attributed the virulence of B. cereus and other virulent endophthalmitis pathogens to toxin production. For Bacillus however, toxins are not the complete story. Bacillus is also motile, and migrates throughout the eye in a short period of time, inciting an explosive intraocular inflammatory response in its wake. This inflammatory response is likely the result of breakdown of the protective blood ocular barrier in response to infection, the triggers of which are presently being investigated. In addition, during infection, retinal architecture collapses and retinal function drops precipitously. We hypothesize that either Bacillus or its toxins (or both) target specific cells in the retina that are involved in protection by the blood ocular barrier (retinal pigment epithelial [RPE] cells) or retinal function itself (Muller cells, photoreceptor cells), leading to the detrimental effects observed during infection. Since the ultimate goal of therapy is to kill offending organisms, arrest inflammation, and preserve organ function, an important goal is to develop more effective therapeutic regimens, with newer antibiotics, anti-inflammatory agents, and/or novel drugs that target bacteria- and host-derived virulence factors in order to prevent blindness.

Current Personnel

Phillip Coburn, Ph. D., Assistant Professor of Research, Ocular Bacterial Pathogenesis

Roger Astley, Research Technician, Pathogenesis of Endophthalmitis

​Austin LaGrow, Research Technician, Pathogenesis of Endophthalmitis

MD Huzzatul Mursalin, Graduate Student

Select Publications

Wiskur BD, Woods DC, Wheatley NR, Callegan MC. Update on Improvements for Therapy of Severe Bacterial Endophthalmitis. Proc 8th Intl Soc Ocul Pharmacol Ther  2010, 25-38. 

Olson R, Donnenfeld E, Bucci F, Price F, Raizman M, Solomon K, Devgan U, Trattler W, Dell S, Wallace RB, Callegan M, Brown H, McDonnell PJ, Conway T, Schiffman RM, Hollander DA. Methicillin Resistance of Staphylococcus Species Among Healthcare and Non-Healthcare Workers Undergoing Cataract Surgery. Clin Ophthalmol 2010 Dec 10;4:1505-14

Callegan MC, Woods D, Guess S, Wheatley N, Leonard R. Efficacy of Vitrectomy and Intravitreal Vancomycin for the Treatment of Bacillus cereus Endophthalmitis. Retina. 2011 Sep;31(8):1518-24.

Hunt JJ, Wang J-T, Callegan MC. Role of capsular antigen in experimental Klebsiella pneumoniae endophthalmitis. Invest Ophthalmol Vis Sci, Invest Ophthalmol Vis Sci. 2011 Aug 29;52(9):6860-6. Print 2011 Aug

Novosad B, Astley R, Callegan MC. Role of Toll-like receptor (TLR) 2 in experimental Bacillus cereus endophthalmitis. PLoS ONE 6(12): e28619. doi:10.1371/journal.pone.0028619, 2011.

Coburn PC, Wiskur BJ, Callegan MC. Endogenous endophthalmitis is associated with vascular permeability in diabetes. Invest Ophthalmol Vis Sci. 2012 Nov 1;53(12):7426-31. doi: 10.1167/iovs.12-10661. PMID: 23036996 PMCID:PMC3487485

1Pettey JH, Mifflin MD, Kamae K, McEntire MW, Pettey DH, Callegan MC, Brown H, Olson RJ. The impact of short term topical gatifloxacin and moxifloxacin on bacterial injection after hypodermic needle passage through human conjunctiva. J Ocul Pharmacol Ther. 2013 Jun;29(5):450-5. PMID:23425429

Hunt JJ, Astley R, Wang J-T, Callegan MCTLR4 Contributes to the Host Response to Klebsiella Intraocular Infections. Curr Eye Res. 2014 Aug;39(8):790-802. PMID:24588082

Parkunan SM, Astley R, Callegan MC. Role of TLR5 and Flagella in Bacillus Intraocular Infection. PLoSOne 2014 Jun 24;9(6):e100543. PMID:24959742 PMCID:PMC4068998

Li X, Gu X, Boyce T, Zheng M, Reagan A, Mandal N, Cohen A, Callegan M, Carr D, Elliott M. Caveolin-1 increases the pro-inflammatory chemoattractants and blood-retinal barrier breakdown but decreases leukocyte recruitment in inflammation. Invest Ophthalmol Vis Sci. 2014 Aug 26;55(10):6224-34. doi: 10.1167/iovs.14-14613. PMID:25159208 PMCID:PMC4183075