The SapA Protein Is Involved in Resistance to Antimicrobial Peptide PR-39 and Virulence of .

Antimicrobial peptides are essential to the innate immune defense of the mammal against bacterial infection. However, pathogenic bacteria have evolved multiple strategies to resist and evade antimicrobial peptides, which is vital to bacterial survival and colonization in hosts. PR-39 is a linear porcine antimicrobial peptide containing 39 amino acid residues with a high proline content. Resistance to antimicrobial peptide PR-39 has been observed in . However, little is known about the factors required for this resistance. In the present study, PR-39 exposure increased the expression of the gene in . The gene, which encodes a putative peptide transport periplasmic protein, was deleted from this bacterium. The Δ mutant showed increased sensitivity to PR-39 compared to the wild-type MD12 and complemented PΔ strains. However, the Δ mutant did not exhibit any alterations in outer membrane integrity. Scanning electron microscopy showed that the Δ mutant displayed morphological defects, as indicated by a deformed and sunken shape after PR-39 treatment. In addition, disruption of the SapA protein led to reduced colonization and attenuated virulence of in the BALB/c mouse model. Collectively, these data suggest that SapA acts as one mechanism for to counteract PR-39-mediated killing. To the best of our knowledge, this is the first study to show a mechanism underlying antimicrobial peptide resistance in .