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2004 OMIG, Abstract 6

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Corneal Virulence of Non-Capsular Streptococcus pneumoniae
ME Marquart, JM Reed, RJ O'Callaghan, DO Girgis, CC McCormick, AR Caballero. Department of Microbiology,
Immunology, and Parasitology, Louisiana State University, New Orleans, Louisiana

Purpose: Determine the corneal virulence of non-capsular S. pneumoniae relative to a capsular strain in a rabbit keratitis model, and compare corneal virulence to a mouse model of peritonitis.
Methods: Mice were infected intraperitoneally with 105 colony-forming units (CFU) of Avery's strain (capsular type 2) or strain R6 (a non-capsular derivative of type 2), and mortality was monitored daily. Additionally, 105CFU of each strain was injected into rabbit corneas. Bacterial loads in rabbit corneas (log CFU per cornea) were determined at 20 or 48 hours post-infection. Slit lamp examination (SLE) of rabbit eyes was performed at 24, 36, and 48 hours post-infection. Pneumolysin production was determined by measuring the hemolysis of rabbit erythrocytes mediated by dilutions of supernatants of each strain grown for 48 hours at 37°C in Todd Hewitt broth.
Results: 100% mortality was observed in mice infected intraperitoneally with the capsular strain by 2 days post-infection, whereas all mice infected with the non-capsular strain survived for 21 days. In contrast, the non-capsular strain caused the same pathologic effects in the rabbit cornea as the capsular strain at 24, 36, and 48 hours post-infection (p >0.158). Mean bacterial log CFU ± SEM recovered at 20 hours post-infection were 7.07 ± 0.09 for the capsular and 6.53 ± 0.12 for the non-capsular strain (p = 0.001). Bacteria recovered from the corneas at 48 hours post-infection were 6.70 ± 0.35 and 1.81 ± 0.46 for the capsular and non-capsular strains, respectively (p < 0.001). The pneumolysin titer of each strain was found to be comparable; partial hemolysis was observed to a titer of 8.
Conclusions: The non-capsular strain was avirulent in the mouse peritoneum, as expected. However, in the rabbit cornea, the S. pneumoniae non-capsular strain was as virulent as the capsular strain.

Disclosure code: N

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