Bacterial endophthalmitis: therapeutic challenges and host-pathogen interactions

Abstract

Endophthalmitis is an infection of the posterior segment of the eye that frequently results in loss of vision. This devastating result occurs despite prompt and often aggressive therapeutic and surgical intervention. Over the past decade, research has centered on determining the bacterial and host factors involved in this potentially blinding disease. The initial focus on the bacterial factors responsible for intraocular virulence has recently expanded into analysis the inflammatory response to infection, including the molecular and cellular interactions between the pathogen and host. This review discusses the epidemiology and therapeutic challenges posed by endophthalmitis, as well as recent findings from the analysis of interactions between the host and pathogen. Based on these findings, a model for the pathogenesis of endophthalmitis is presented. A more comprehensive understanding of the molecular and cellular interactions taking place between pathogen and host during endophthalmitis will expose possible therapeutic targets designed to arrest the infection and prevent vision loss.

Figure 1. Retinal function loss following intravitreal injection of wild type and quorum sensing-defective Bacillus cereus and supernatants

Mouse eyes were injected into the mid-vitreous with approximately 100 CFU/100 μl of wild type (◆) or plcR- (□) B. cereus or 100 μl of a 10-hour sterile filtered culture supernatant of wild type (▲) or plcR- (○) B. cereus. Data at each time point are presented as the percentages of A-wave or B-wave amplitude of retinal function retained compared to baseline and sham-injected controls. Data was averaged for each group and compared using the Student t test. Values and error bars represent means ± standard errors of the means for four or more eyes per group.

Figure 2. Bacterial growth, retinal function loss, and histological analysis of intravitreal injection of Klebsiella pneumoniae

Mouse eyes were injected into the mid-vitreous with approximately 100 CFU/0.5 μl of an ocular isolate of K. pneumoniae. A) Bacterial growth (△) is presented as CFU / whole mouse eye. Retinal function (■) is presented as the percentage of B-wave amplitude of retinal function retained compared to baseline and sham-injected controls. Bacterial counts and retinal function data were averaged for each group and compared using the Student t test. Values and error bars represent means ± standard errors of the means for four or more eyes per group. B) Eyes were harvested at 0, 6, and 12 hours postinfection and following routine histological preparation, were stained with hematoxylin and eosin. By 12 hours postinfection, eyes exhibited only mild posterior and anterior segment inflammation, and retinal layers remained esssentially intact, despite the number of bacteria in the eye and degree of retinal function loss occurring at that time. Magnification, ×5.

Figure 3. Changes in membrane and tight junction integrity of retinal pigment epithelial cell (RPE) monolayers in response to B. cereus infection

RPE (ARPE19, American Type Culture Collection, Manassas VA) were propagated to confluency in Dulbecco’s Minimal Essential Medium/F-12 (1:1) supplemented with 5% fetal bovine serum and 1% glutamine in 24 well tissue culture plates or on glass coverslips. Monolayers were infected with 10⁵ CFU wild type or quorum sensing-defective plcR- B. cereus. A) Membrane permeability was analyzed detecting the release of lactate dehydrogenase (LDH) release at 0, 2, 4, 6, and 8 hours (CytoToxONE, Promega, Madison WI). Values represent the mean ± standard deviation of six or more samples per time point. B) Integrity of the tight junction protein ZO-1 was analyzed by immunohistochemistry. At 0 or 2 hours postinfection, RPE monolayers on glass coverslips were incubated with mouse anti-ZO-1 (1:200, Zymed^®/Invitrogen, Carlsbad CA) and goat-anti-mouse (1:200, Alexafluor 488; Molecular Probes™/Invitrogen). Coverslips were analyzed by confocal microscopy (Olympus FluoView FV500, Center Valley PA). Areas of intact ZO-1 are designated by arrowheads. Loss of ZO-1 integrity was observed after 2 hours of infection with wild type B. cereus, but not the plcR- mutant. Magnification, ×100.