Survival of Serratia marcescens in the Presence of Complement
Hume, E. B. H.
Willcox, M. D. P.
- Publisher: Microbial Ecology in Health and Disease
Microbial Ecology in Health and Disease
Serratia marcescens has been isolated from a variety of ocular infections and/or infammation. In order to survive in the eye, strains must be able to resist host defence systems. Complement has been shown to have an increased concentration and to be active during sleep. Not only is the complement system involved in host defence, but its activation can also produce in ammation. The aim of the present study was to examine the ability of ocular isolates of S. marcescens to withstand complement attack, activate complement and to examine the mechanisms used for evasion of this host defence system. The majority of isolates tested (4/6) were resistant to complement attack. These isolates were able to activate both complement pathways, as detected by enzyme-linked immunosorbent assays (ELISA) and western blotting assays. Components detected included C4, Factor B, C3 and C5. Possible mechanisms of resistance were elucidated including quantity of lipopolysaccharide (LPS) on the cell surface, ability to bind lactoferrin, types of complement components deposited onto the surfaces of strains, and the amount and location of C3 bound on the surface, as determined by transmission electron microscopy. Complement-resistant strains generated iC3b, bound more lactoferrin (1.7±0.6 for resistant cells compared with 0.4±0.2 for complement-sensitive cells, relative values), and had larger amounts of extractable endotoxin (216.8±88.8 µg/ml for resistant strains and 36.0±48.4 µg/ml for sensitive strains). Although there was no direct correlation between the ability to resist and activate complement and the isolation of strains from symptomatic or asymptomatic eyes, the resistance of strains to complement may allow these strains to remain in the eye and the activation of complement may contribute to the in ammatory response seen during infection or ocular infammation.Keywords: Serratia marcescens, complement, host defence, tear ?film.