Serratia marcescens keratitis: strain-specific corneal pathogenesis in rabbits

The purpose of this study was to develop an animal model of Serratia keratitis that is suitable to demonstrate the pathology of specific strains.

Serratia marcescens ocular strains 93-1399-1 and 94-EI-185-2, and an environmental strain (ATCC 14041) were characterized in vitro in terms of their motility, metabolic profiles, ribotypes, and protease production. The strains were then analyzed in the rabbit intrastromal injection model. Slit lamp examination (SLE) and enumeration of bacteria in the cornea was conducted every 6 hours for 30 hours post-infection. In vivo motilities were analyzed by quantification of bacteria in the peripheral and central areas of infected rabbit corneas.

All strains were similar in their metabolic activity and production of extracellular proteases. The ocular isolates were distinct from the environmental strain in their ribotyping patterns and in their motility. Each strain grew logarithmically in the cornea up to 6 hours post-infection. SLE 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 maximum at 18 hours post-infection. Strain-specific differences in pathology were noted from 18 to 30 hours post-infection. Strain 94-EI-185-2 produced iritis but only mild corneal changes. Strain 93-1399-1 produced a severe corneal infiltrate encompassing the entire corneal surface as well as severe conjunctival inflammation and iritis. Strain ATCC 14041 produced a localized, severe, exudative corneal abscess that contained infecting bacteria.

A rabbit model of Serratia keratitis was developed in which bacterial growth kinetics and strain-specific ocular pathologic changes were reproducible.