2005 OMIG, Abstract 8

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CRC is Involved in Biofilm Formation and Corneal Virulence of Pseudomonas aeruginosa (PA14) in Corneal Infection of C57B/6 Mice

Michael E. Zegans^1,2, Dan MacEachran¹, George A. O'Toole¹

¹Department of Microbiology and Immunology ²Department of Surgery (Immunology) Dartmouth Medical School, Hanover, NH

Purpose: The catabolite repression control gene (crc) regulates in catabolite repression allowing for preferential utilization of different carbon sources by Pseudomonas aeruginosa (PA). Mutations of this gene are known to reduce biofilm formation under certain conditions. Based on our earlier work, we investigated whether these mutant strains would have altered virulence in a scratch model of bacterial keratitis in mice.

Methods: A corneal scratch model of bacterial keratitis was employed using C57B/6 mice and an inoculum of 10⁵ colony forming units (cfu). Infections were evaluated by grading the corneal appearance and by determination of cm recovered from eyes at 4 and 48 hrs.

Results: A dramatic reduction of virulence was noted for the crc mutant. The mean stromal opacity score at day 2 was 2.75 for wild type PA14 and 0.25 for the crc mutant. Likewise, the mean cfu count for corneas inoculated with the crc mutant was 1.05 x l0⁴ cfu/ml at 4 hours after inoculation, but dropped to 550 cfu/ml at 48 hours. However, corneas inoculated with wild type PA14 had a cm count of 8.25 x 10³ cfu/ml at 4 hours and increased to 5.0 x 10⁵ at 48 hours.

Conclusions: A knock out of the crc gene results in a dramatic decrease in biofilm formation and corneal virulence. This association between crc and corneal virulence has not previously been described. An understanding of carbon source utilization by PA may reveal opportunities to alter the virulence of PA.

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