Research in the Marquart laboratory focuses on ocular bacterial infections, particularly those caused by Streptococcus pneumoniae. The three types of ocular infections caused by bacteria are conjunctivitis (pink eye), keratitis (corneal disease), and endophthalmitis (disease of the aqueous and/or vitreous humors). S. pneumoniae is a major cause of conjunctivitis and is often identified within the top three causes of keratitis. Moreover, streptococcal species as a whole are significant causes of exogenous endophthalmitis following ocular surgery and intravitreal injections. Two of the pneumococcal virulence factors studied by the Marquart laboratory in the context of keratitis and endophthalmitis are the outer polysaccharide capsule and the cholesterol-dependent cytolysin, pneumolysin. Both the capsule and pneumolysin have been previously determined to be important in the pathogenesis of a variety of the classically known pneumococcal diseases such as pneumonia and otitis media. Marquart’s group determined that the pneumococcal capsule is important for clinical disease severity and bacterial replication in S. pneumoniae endophthalmitis, but is unimportant for S. pneumoniae keratitis. Pneumolysin, which is a virulence factor for both diseases, has been successfully targeted with immunization strategies and topical cholesterol treatment. At the cellular level, pneumolysin binds to lipid rafts within the cell membranes of human corneal epithelial cells. The presence of pneumolysin is also responsible in part for the recruitment of neutrophils to the cornea or the vitreous humor during infection. More recent studies have turned to determining the factors involved in pneumococcal metabolic fitness. S. pneumoniae is a fastidious bacterium; however, this organism replicates to high quantities in the vitreous humor. In an effort to determine which bacterial genes are essential for fitness, negative selection of a library of pneumococcal mutants in the vitreous humor is being employed. Genes negatively selected are providing clues to the identities of host vitreous substrates for metabolism and fitness.Other research interests of the Marquart laboratory include the Viridans Group Streptococci (VGS) in endophthalmitis, S. pneumoniae pneumonia and septicemia, and Pseudomonas aeruginosa keratitis. Dr. Marquart also maintains ongoing collaborations within the Department of Microbiology and Immunology, and with the Department of Biomedical Material Science, Department of Ophthalmology, Mississippi State University, The University of Mississippi (Oxford), and various industry partners.