Serratia marcescens keratitis: Strain-specific corneal pathogenesis in rabbits

Purpose. The purpose of this study was to develop an animal model of Serrat ia keratitis that is suitable to demonstrate the pathology of specific stra ins. Methods. Serratia marcescens ocular strains 93-1399-1 and 94-EI-185-2, and an environmental strain (ATCC 14041) were characterized in vitro in terms o f their motility, metabolic profiles, ribotypes, and protease production. T he strains were then analyzed in the rabbit intrastromal injection model. S lit lamp examination (SLE) and enumeration of bacteria in the cornea was co nducted every 6 hours for 30 hours postinfection. In vivo motilities were a nalyzed by quantification of bacteria in the peripheral and central areas o f infected rabbit corneas. Results. All strains were similar in their metabolic activity and productio n of extracellular proteases. The ocular isolates were distinct from the en vironmental strain in their ribotyping patterns and in their motility. Each strain grew logarithmically in the cornea up to 6 hours post-infection. SL E scores increased from 0 to 30 hours post-infection for strains ATCC 14041 and 93-1399-1, while the SLE score of strain 94-EI-185-2 reached its maxim um at 18 hours post-infection. Strain-specific differences in pathology wer e noted from 18 to 30 hours post-infection. Strain 94-EI-185-2 produced iri tis but only mild corneal changes. Strain 93-1399-1 produced a severe corne al infiltrate encompassing the entire corneal surface as well as severe con junctival inflammation and iritis. Strain ATCC 14041 produced a localized, severe, exudative corneal abscess that contained infecting bacteria. Conclusions. A rabbit model of Serratia keratitis was developed in which ba cterial growth kinetics and strain-specific ocular pathologic changes were reproducible.