Abstract
BackgroundCapsule and pneumolysin (PLY) are two major virulence factors of Streptococcus pneumoniae. S. pneumoniae is one of the leading causes of bacterial endophthalmitis. The aim of this study is to determine whether passive immunization with the 23-valent pneumococcal polysaccharide vaccine (Pneumovax® 23; PPSV23) or PLY protects against pneumococcal endophthalmitis.MethodsNew Zealand white rabbits were passively immunized with antiserum to PLY, PPSV23, a mixture of PPSV23/PLY, or PBS (mock). Vitreous was infected with a clinical strain of S. pneumoniae. In a separate group of experiments, vancomycin was injected 4 hours post-infection (PI) for each passively immunized group. Severity of infection, bacterial recovery, myeloperoxidase (MPO) activity and percent loss of retinal function were determined.ResultsPassive immunization with each antiserum significantly lowered clinical severity compared to mock immunization (PPSV23 = 9.19, PPSV23/PLY = 10.45, PLY = 8.71, Mock = 16.83; P = 0.0467). A significantly higher bacterial load was recovered from the vitreous of PLY passively immunized rabbits 24 hours PI (7.87 log10 CFU) compared to controls (7.10 log10 CFU; P = 0.0134). Retinas from immunized rabbits were more intact. Vitreous of PLY (2.88 MPO untis/mL) and PPSV23/PLY (2.17) passively immunized rabbits had less MPO activity compared to controls (5.64; P = 0.0480), and both passive immunizations (PLY = 31.34% loss of retinal function, PPSV23/PLY = 27.44%) helped to significantly preserve retinal function compared to controls (64.58%; P = 0.0323). When vancomycin was administered 4 hours PI, all eyes were sterile at 24 hours PI. A significantly lower clinical severity was observed for rabbits administered the combination immunization (5.29) or PPSV23 (5.29) with vancomycin treatment compared to controls (17.68; P = 0.0469).ConclusionsPassive immunization with antisera to these antigens is effective in reducing clinical severity of pneumococcal endophthalmitis in rabbits. Addition of vancomycin to immunization is effective at eliminating the bacteria.
Highlights
Capsule and pneumolysin (PLY) are two major virulence factors of Streptococcus pneumoniae
Two pneumococcal vaccines are currently licensed for use in the United States and are based on the polysaccharide capsule, the 13-valent conjugate vaccine (Prevnar 13W; Pfizer, New York, NY, USA) and the 23-valent polysaccharide vaccine (PneumovaxW 23; PPSV23; Merck, Whitehouse Station, NJ, USA) [17,18,19]
These findings led to the question of whether PPSV23 could protect the eye from damage observed during pneumococcal endophthalmitis
Summary
Capsule and pneumolysin (PLY) are two major virulence factors of Streptococcus pneumoniae. The aim of this study is to determine whether passive immunization with the 23-valent pneumococcal polysaccharide vaccine (PneumovaxW 23; PPSV23) or PLY protects against pneumococcal endophthalmitis. Robbins et al [18] observed 90% protection from blood isolates and 85% protection from colonization of normally sterile sites by S. pneumoniae with these serotypes. Regarding ocular studies, this laboratory previously showed that capsule is important for pneumococcal endophthalmitis [21]. Capsule was determined to be important for infection and retinal damage in this model These findings led to the question of whether PPSV23 could protect the eye from damage observed during pneumococcal endophthalmitis
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