Faculty Bibliography

We used a rabbit endophthalmitis model to explore the role of fsrB, a gene required for the function of the fsr quorum-sensing system of Enterococcus faecalis, in pathogenicity. A nonpolar deletion mutant of fsrB had significantly reduced virulence compared to wild type. Complementation of mutation restored virulence. These data corroborate the role of fsrB in E. faecalis pathogenesis and suggest that the rabbit endophthalmitis model can be used to study the in vivo role of quorum sensing.

PURPOSE: To determine the effect of prophylactic intravenous imipenem on experimental Staphylococcus aureusendophthalmitis. METHODS: The right eyes of 36 New Zealand albino rabbits received an intraocular injection of 100, 1,000, or 10,000 colony-forming units (CFU) of S. aureus. Each of these three groups was subdivided into a control group (no antibiotic prophylaxis) and a prophylactic group, which received 37.5 mg/kg imipenem 8 h prior to inoculation of bacteria, 30 min prior to inoculation of bacteria, and 8 h after inoculation of bacteria. Eyes were observed daily by slit-lamp examination and funduscopy. The eyes were enucleated after 5 and 9 days for the control and prophylactic groups, respectively. Vitreous samples were cultured for bacteria, and the eyes were prepared for histologic evaluation. RESULTS: All eyes that received imipenem demonstrated significantly less inflammation (two-way analysis of variance; P<0.001) on clinical examinations than did control eyes. The prophylactic groups that had received 100 CFU and 1,000 CFU of bacteria also had significantly fewer positive vitreous cultures than the corresponding controls (chi(2) test; P<0.001 and P<0.01, respectively). Histologically, the prophylactic groups injected with 100 CFU and 1,000 CFU of bacteria had significantly less inflammation than the control groups (Student's t-test; P<0.00001 and P<0.0001, respectively). There was no significant difference in the number of positive vitreous cultures or histologically between the control and prophylactic groups that received 10,000 CFU of bacteria. CONCLUSIONS: Prophylactic intravenous imipenem can prevent or significantly reduce the severity of experimental endophthalmitis

Endophthalmitis is an important disease of the eye that is most frequently caused by postoperative and post-traumatic introduction of bacteria into the posterior segment of the eye. In the case of severe infections, visual acuity is greatly damaged or completely lost. Much work has focused on the ability of planktonic bacteria to cause infection and ocular damage while little work has focused on chronic infections in endophthalmitis mediated by the formation of bacterial biofilms on the surface of the lens. This review focuses on the interaction of Staphylococcus aureus and Staphylococcus epidermidis lens-associated biofilms in endophthalmitis. Additionally, this review highlights some relevant biofilm-immune system interactions and outlines a new in vivo mouse model to explore biofilm-related infections in endophthalmitis.

OBJECTIVE: To compare a new rapid antibiotic susceptibility test (RAST) to the conventional method in patients with endophthalmitis. DESIGN: Prospective nonrandomized comparative trial. PARTICIPANTS: Intraocular aspirates from 24 consecutive patients with endophthalmitis were tested. METHODS: Approximately 0.25 ml of vitreous or anterior chamber aspirate was obtained and tested for antibiotic sensitivity using the Kirby-Bauer agar disk diffusion method. Using this conventional testing method, the aspirates were cultured for bacterial growth before antibiotic susceptibility testing (AST). In contrast, for direct RAST, the aspirates were inoculated directly onto agar plates with antibiotic disks without first culturing for bacterial growth. RESULTS: Of the 24 endophthalmitis aspirates studied, 4 (17%) could not be tested by direct RAST because either more than one bacterial species was present or no bacteria were cultured. The remaining 20 cases provided 467 antibiotic-microorganism combinations. The two methods yielded identical susceptibility results in 409 (88%) of the 467 tests. In 42 tests (9%), a minor discrepancy occurred between the conventional method and RAST, in which one resulted in intermediate susceptibility, whereas the other was either resistant or sensitive. Significant discrepancy, defined as a bacterial sample reported as sensitive in one method yet resistant in the other, occurred with 16 samples (3%). Results of the RAST were available within 6 to 10 hours compared with more than 24 hours for the conventional method. Of clinical significance, the results of the RAST revealed that in 11 cases of epidemic Stenotrophomonas maltophilia endophthalmitis, the bacteria were resistant to the antibiotics prescribed, and change of antibiotic therapy was made on the basis of the RAST results. CONCLUSIONS: RAST provided accurate antibiotic susceptibility results in a much shorter time than did the conventional method. We suggest that conventional AST be performed for confirmation of the RAST results, but initial antibiotic therapy can quite reliably be based on the results of RAST

Endophthalmitis is a severe inflammation of the interior of the eye caused by the introduction of contaminating microorganisms following trauma, surgery, or hematogenous spread from a distant infection site. Despite appropriate therapeutic intervention, bacterial endophthalmitis frequently results in visual loss, if not loss of the eye itself. Although the pathogenicity of bacterial endophthalmitis has historically been linked with toxin production during infection, a paucity of information exists as to the exact mechanisms of retinal toxicity and the triggers for induction of the intraocular immune response. Recently, research has begun to examine the bacterial and host molecular and cellular events that contribute to ocular damage during endophthalmitis. This review focuses on the causative agents and therapeutic challenges of bacterial endophthalmitis and provides current data from the analysis of the role of bacterial virulence factors and host inflammatory interactions in the pathogenesis of eye infections. Based on these and related studies, a hypothetical model for the molecular pathogenesis of bacterial endophthalmitis is proposed. Identifying and understanding the basic mechanisms of these bacterium-host interactions will provide the foundation for which novel, information-based therapeutic agents are developed in order to prevent vision loss during endophthalmitis.

OBJECTIVE: To study whether the clinical outcome of Staphylococcus epidermidis-induced endophthalmitis in rabbits is related to the antibiotic resistance pattern of the infecting strain. DESIGN: Experimental animal study. PARTICIPANTS: The right eyes of 36 New Zealand white albino rabbits were inoculated with strains of S. epidermidis that displayed various patterns of antibiotic resistance. METHODS: There were 12 rabbits in each of three study groups: fully antibiotic susceptible (FS), partially antibiotic resistant (PR), and multiresistant (MR). Five days after inoculation, the eyes were enucleated and prepared for histologic studies. MAIN OUTCOME MEASURES: Comparisons among the three groups were made based on electroretinographic (ERG) findings, histologic evaluation by a masked observer, and clinical examination. RESULTS: Electroretinographic findings on all rabbits were made by an unmasked observer. At 30 hours after inoculation, the ERG was diminished to 65% of normal for group FS, compared with a flat ERG waveform for groups PR (P < 0.05) and MR (P < 0.05). The ERG waveform was flat for all three groups at 72 hours after inoculation. Histologic evaluation by use of a histologic score revealed that the degree of inflammation and destruction of the retina was less for group FS (n = 10) compared with groups PR (n = 8) and MR (n = 8). Clinical examination revealed that there was a trend of less ocular inflammation for group FS compared with groups PR and MR. CONCLUSIONS: In a rabbit model of S. epidermidis-induced endophthalmitis, antibiotic-susceptible strains caused less inflammation and destruction of the infected retina than did antibiotic-resistant strains

BACKGROUND: Propionibacterium acnes has been described as a causative agent of postoperative endophthalmitis. This gram-positive, immotile, non-spore-forming bacterium is highly pleomorphic and grows under conditions of low to no oxygen concentration. It is commonly found on the skin at the openings of sebaceous glands and on hairs. A near-symptomless postoperative endophthalmitis occurs particularly when Propionibacteria are enclosed in the capsular bag. We investigated to what extent the number of P. acnes in the conjunctival sac can be reduced by preoperative disinfection with polyvidone iodine (1%). PATIENTS AND METHODS: A total of 261 patients with intrabulbar surgery had two conjuctival swabs taken: the first immediately prior to preoperative preparation in the operating theatre, following in-patient application of antibiotic eye drops (Polymyxin-B-sulfat, Neomycinsulfat and Gramicidin in combination); the second swab was taken after disinfection with polyvidone iodine before opening the conjunctiva. RESULTS: Of the 261 swabs, 60 (23%) taken prior to polyvidone iodine application were positive for Propinibacterium acnes. Following polyvidone iodine treatment, a further 5 (1.9%) remained culture-positive. After disinfection, 55 (92%) of the 60 positive swabs for Propionibacterium acnes remained culture-negative. CONCLUSIONS: We concluded that a significant reduction of P. acnes can be achieved by preoperative application of polyvidone iodine (1%) (P < 0.001)