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Posters
November 2001
CONTACT LENS INDUCED PERIPHERAL ULCERATION
(CLPU) MAY BE PRODUCED BY ALPHA TOXIN DEFICIENT MUTANT OF S AUREUS
AND ITS PARENT STRAIN.
P.Z.J. Wu, E. Hume, A. Thakur, F. Stapleton, M.D.P. Willcox
Cooperative Research Centre for Eye Research and Technology, University
of New South Wales, Australia.
Purpose:
S. aureus has been suggested to be
responsible for CLPU. However, the pathogenesis of CLPU
is not well understood. An animal model of CLPU has been
produced in rabbits. The aim of this experiment is to examine
the difference of the pathogenicity of an alpha-toxin-deficient
mutant and its parent strain, and the role of alpha-toxin
in the production of CLPU.
Method:
S. aureus NCTC 8325-4 and
its alpha-toxin-deficient mutant DU 1090 were examined for
their abilities to produce proteolytic enzymes and hyaluronidase
on agar plates with the corresponding substrates. The production
of elastase was tested spectrophotometrically using concog-red
elastin. Alpha-toxin and beta-toxin production were tested
by measuring the bacteria's abilities to cause hemolysis on
rabbit and sheep blood respectively. The bacterial strains
were then used on rabbits with an artificial corneal epithelial
defect, and corneal lesions were produced when the rabbits
were allowed to wear contact lens coated with each strain
of S. aureus on either eye of the same rabbit. The clinical
pictures, bacteriological cultures and histology of the corneal
ulceration on both eyes were examined and compared.
Results:
Both strains of S. aureus
were found to be able to produce caisinase, gelatinase, hyaluronidase
elastase and beta-toxin to the same extent. S. aureus DU1090
caused weak hemolysis to the rabbit red blood cells, while
S. aureus 8325-4 causing strong hemolysis, which reflected
their difference in alpha-toxin production. Both S. aureus
strains may cause corneal ulceration in contact lens wearing
eyes. In general, corneal ulceration observed in the eyes
wearing DU1090 lens were milder than those seen in the eyes
wearing S. aureus 8325-4 coated lenses. S. aureus 8325-4 may
cause serious infectious keratitis in the rabbit eyes under
the condition in which only CLPU-like lesions were observed
with DU1090.
Conclusions:
The enzyme production
profile of S. aureus DU 1019 was the same as its parent
strain (S. aureus 8325-4). S. aureus strains may produce
CLPU-like lesions regardless the presence of alpha-toxin,
but the corneal lesions caused by alpha-toxin deficient
S. aureus were much milder. S. aureus 8325-4 may cause serious
infectious keratitis.
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