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A. R. Caballero, D. W. Stroman, J. G. Bartell, C. L. Balzli, R. J. O'Callaghan; Genetic Analysis of a New Staphylococcus aureus Isolate that Exhibits Exquisite Virulence in the Rabbit Cornea, Conjunctiva and Anterior Chamber. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5112.
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S. aureus is a leading cause of ocular infections including keratitis, conjunctivitis, and endophthalmitis. The study of these conditions have been handicapped by the lack of animal models in which S. aureus grows on the corneal surface, in the conjunctiva, or in the anterior chamber. We have isolated a strain of S. aureus that grows and causes severe pathology in each of these three sites in rabbits. To determine what makes this strain unique, we have conducted metabolic and genetic analysis and compared the results with similar data from other laboratory and clinical strains of S. aureus.
S. aureus strain UMCR1, a conjunctival isolate, was tested for sensitivity to 28 antibiotics. Its nutritional requirements were analyzed in 96 separate tests. Concentrated culture supernatant was analyzed for protease activity by gelatin zymography. Its relatedness to other S. aureus strains was determined by ribotyping. Whole genome mapping was used to compare its genome to 34 other strains.
S. aureus strain UMCR1 was shown to be sensitive to all tested antibiotics except sulphamethoxazole. Its metabolic requirements were similar to the other S. aureus strains tested in 94 of 96 tests. UMCR1 did not secrete any protease with gelatinase activity. Ribotyping comparison against 39 strains of S. aureus resulted in ribogroup similarities ranging from 91 to 99 per cent. UMCR1 was found by whole genome mapping analysis to be closely related to two S. aureus strains, including MW2, a highly virulent community acquired MRSA strain. UMCR1 has a 51.7 Kb insert at position 351,874, that is not found in the 14 S. aureus isolates whose genome have been fully sequenced (including MW2).
S. aureus UMCR1 is a highly virulent organism in animal models of ocular infection. The genomic organization of this isolate is most similar to S. aureus MW2. These two isolates form a unique cluster within the clade formed by the 14 fully sequenced S. aureus strains, suggesting that UMCR1 could be a member of a newly emerging subset of virulent S. aureus.
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