Role of Agr Quorum Sensing System in the Pathogenesis of Keratitis Caused by Staphylococcus aureus

1. Takashi Suzuki^1,2
2. Yuichi Ohashi²
3. Michael S Gilmore¹

¹Ophthalmology, Harvard Medical School, Boston, U.S.A.
²Ophthalmology, Ehime University, Graduate School of Medicine, Toon, Japan.

Purpose: Staphylococcus aureus is commensal bacterium of the ocular adnexa such as conjunctiva sac or lid, and often causes keratitis. The Agr quorum sensing system is a central regulator of virulence, and there are four variations on the agr locus. Little is known about the role of agr quorum sensing in establishment of keratitis. This study was designed to investigate the possible contribution of agr quorum sensing system.

Methods: The strains used were S. aureus parental strains (RN6390) and their isogenic S. aureus mutants defective in agr system (RN6390Δagr). To determine the role of agr in destruction of tight junction in vitro, RN6390 or RN6390Δagr (105CFU/ml) were exposed to human cultured corneal epithelial cells (HCEC) for 8 h. Trans epithelial electrical resistance (TER) and immune staining of tight junction protein (Occuldin and ZO-1) was used for evaluation of tight junction damage. Furthermore possession or variation of the agr locus for 5 S. aureus keratitis isolates was determined using PCR and sequencing.

Results: In vitro, the infection with RN6390 resulted in a significantly greater reduction of TER value than that with RN6390Δagr. Immune staining showed that tight junction was profoundly destroyed in HCEC infected with RN6390 but not HCEC infected with RN6390Δagr. All keratitis isolates have agr loci. Three isolates are agr type 2 and two are type 4.

Conclusions: The agr system is central to the loss of tight junctions, and all S. aureus keratitis isolates possess intact loci, indicating its importance in vivo.