Differential Expression of the System by Antimicrobial Peptide LL-37 in Commensal and Clinical Isolates.

The three-component system senses and responds to cationic antimicrobial peptides (CAMPs), which induces the expression of the operon and the genes and , modifying the surface net charge in , resulting in the repulsion of CAMPs. The system has been only studied in the 1457 strain, and there are no studies of prevalence and level of expression of in commensal and clinical isolates. From 60 isolates, those selected from commensal healthy skin (n = 20), commensal healthy conjunctive (n = 10), and clinical ocular infection (n = 30) presented the , and genes in their genomes. Constitutive expression of , and genes was determined by RT-qPCR in all isolates. It was found that expression of , and was 3.3-5.9-fold higher in commensal isolates stimulated with LL-37 (15 µg/mL) than in clinical isolates. Similarly, expression of the operon and the genes , and was 8-10-fold higher in commensal isolates than in clinical. However, LL-37 did not increase the addition of lysine in the phospholipids of the cytoplasmic membrane in any of the isolates. Mutations in the loop region, , and their promoter sequence were not found. These results demonstrated that system is essential in all isolates for its constitutive expression; however, LL-37 caused an increase of expression in commensal isolates, suggesting that isolates do not respond in the same way to the presence of LL-37.