Effect of Salicylic Acid on the Membrane Proteome and Virulence of Pseudomonas aeruginosa.

PURPOSE This study aimed to determine the effect of salicylic acid on the membrane proteome, sensitivity to antibiotics, and production of microbial keratitis by Pseudomonas aeruginosa. METHODS P. aeruginosa 6294 was grown in the presence or absence of 30 mM salicylic acid. Bacterial membrane proteins were extracted in carbonate buffer, separated using two-dimensional gel electrophoresis and identified by mass spectrometry. The minimum inhibitory concentration (MIC) of various antibiotics was determined using P. aeruginosa 6294 grown in presence or absence of salicylic acid. The scratch mouse model of microbial keratitis was used to determine whether treatment with 30 mM salicylic acid could improve the outcome of infection. RESULTS Growth in salicylic acid altered the membrane proteome of P. aeruginosa 6294. Eighteen proteins, including OprF, OprD, MexA, OprG, PilQ, and flagellin-type A protein, were downregulated, six proteins, including OprM and OprB, were upregulated, and nine proteins were unaffected by growth in salicylic acid. Growth in salicylic acid slightly increased the resistance to carbapenem antibiotics but did not affect MICs of the other antibiotics tested. Salicylic acid treatment significantly reduced the clinical score of eyes and bacterial load in eyes during microbial keratitis but had no effect on numbers of infiltrating neutrophils. CONCLUSION Salicylic acid altered the membrane proteins of P. aeruginosa, slightly increased the resistance of the bacterium to carbapenem antibiotics only, and was able to reduce the pathogenicity associated with P. aeruginosa infection of mouse corneas. Salicylic acid may be useful as an antimicrobial agent in the treatment of Pseudomonas keratitis.