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H. Zhu, R.S. Bandara, E. Hume, F. Stapleton, M.D. Willcox; Ocular Isolates of Pseudomonas aeruginosa Deficient in the las Quorum-Sensing System Are Not Virulent in a Microbial Keratitis Model . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4746.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The Pseudomonas aeruginosa quorum-sensing systems, las and rhl, control the production of numerous virulence factors. Quorum-sensing mutants generated in standard laboratory strains have been demonstrated to be attenuated in virulence during mouse corneal infection. In the present study, the ocular isolates of P. aeruginosa with low quorum-sensing signal molecules and low protease production were examined for their quorum-sensing genes, quorum-sensing controlled phenotypes and their virulence in a scarified mouse model. Methods: Four isolates used in the study were P. aeruginosa strains Paer1 isolated from contact lens-induced acute red eye, Paer2, Paer3 and Paer4 isolated from asymptomatic subjects. Strains 6294 and 6206, isolated from microbial keratitis, were also included as controls. Quorum-sensing genes lasI, lasR, rhlI, rhlR, and quorum-sensing controlled genes lasB (encoding elastase), aprA (encoding alkaline protease) and rhlAB (encoding rhamnolipid) in the strains were determined by using polymerase chain reaction. las system controlled protease production was examined with elastin-Congo red assay and zymography. rhl system controlled rhamnolipid production was evaluated with a plate assay. Induction of P. aeruginosa keratitis was examined in a scarified inbred Balb/c mouse model. Results: All the quorum-sensing genes were detected in P. aeruginosa 6294 and 6206 as expected. Strains Paer1 and Paer3 were lasI and lasR negative. Strains Paer2 and Paer4 were rhlR and rhlAB negative. All strains possessed the other genes examined. Elastase activity was not detected in the Paer isolates although the strains possessed the lasB gene. There was no alkaline protease activity in strains Paer2 and Paer4, however the strains were aprA gene positive. Rhamnolipid was not produced by strains Paer2 and Paer4. Both strains Paer1 and Paer3 were avirulent on scarified mouse corneas. Strains Paer2 and Paer4 induced mouse corneal infection, and the infected eyes showed a similar clinical appearance to the eyes infected by P. aeruginosa 6206. Conclusions: These findings suggest that the deficiency of las or rhl quorum-sensing genes may naturally occur in clinical isolates of P. aeruginosa. las quorum-sensing system seems to play a more important role in development of corneal infection and may become a potential target for developing novel antimicrobial reagents to prevent Pseudomonas keratitis.
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