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S. N. Green, M. E. Sanders, S. A. Robinson, M. E. Marquart; A Comparison of Capsular and Non-Typeable Pneumococcal Clinical Isolates in a Rabbit Conjunctivitis Model. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4728.
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Non-typeable pneumococci have emerged as recent causes of outbreaksof S. pneumoniae conjunctivitis. The purpose of this study wasto determine if a non-typeable clinical conjunctivitis isolatewas more virulent than a capsular isolate in a rabbit modelof conjunctivitis.
Six strains of pneumococci isolated from patients with conjunctivitiswere serotyped by multiplex PCR. New Zealand white rabbits weremaintained according to the ARVO Statement for the Use of Animalsin Ophthalmic and Vision Research. Rabbits were subsequentlyinfected via the ocular conjunctiva with 106 of one of the non-typeableisolates (n = 6) or the serotype 10a isolate (n = 6). Conjunctivaefrom each experimental group and from uninfected conjunctivaewere examined at 24 h post-infection by two examiners.
Five of the conjunctivitis isolates were characterized as non-typeable(non-capsular) and 1 was characterized as serotype 10a. Grossanalysis of conjunctivae infected with the non-typeable strain(Image 1) showed mild chemosis and moderate injection, whereasconjunctivae infected with the serotype 10a (Image 2) strainshowed marked chemosis and profound injection. Clinical scoresfor serotype 10a and the non-typeable strain were 2.8783 ±1.2502 and 1.4833 ± 0.2295, respectively (P = 0.2982).
These findings show that non-typeable pneumococci are not significantlymore virulent than capsular pneumococci in causing bacterialconjunctivitis. Factors other than the ability to establishconjunctivitis may be involved in the prevalence of non-typeablepneumococci as causes of conjunctivitis.
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