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2004
OMIG, Abstract 6
OMIG
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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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