Lung-directed delivery of a ligand-mediated chimeric lysin has an enhanced ability to eradicate pulmonary and intracellular Staphylococcus aureus.

Background: Bacteriophage lysins have high antimicrobial activities with many advantages as alternatives to antibiotics, however, lysins generally do not exhibit intracellular bactericidal capabilities due to a lack of cell-penetrating properties and/or reduced activity under the intracellular environment. To address this problem, p-ClyC, an engineered chimeric lysin with a lung cell-targeting peptide, was used to kill Staphylococcus aureus (S. aureus) in vitro and in vivo.

Methods: p-ClyC was constructed by fusing ClyC with a lung-directed peptide. Antimicrobial activities of the two lysins (ClyC, p-ClyC) against S. aureus were evaluated in vitro and in a murine lung infection model. The cell internalization of the lysins was explored using laser confocal imaging. The intracellular bactericidal efficacies of the lysins and gentamicin were evaluated using intracellular growth inhibition studies. The risk of generating antimicrobial resistance after the lysin or antibiotics treatment was investigated by deep sequencing, MIC and growth rate monitoring.

Results: The bactericidal activity against pulmonary intracellular S. aureus of p-ClyC was obviously promoted. The treatment with p-ClyC made the surviving intracellular bacteria generate less tendence to resistance in terms of growth rates and minor alleles in genomes than the treatment with gentamicin. In murine lung infection model, the survival rate for the group of p-ClyC was significantly improved, and more pulmonary bacteria were killed by the p-ClyC than those by the ClyC.

Conclusions: The lung-directed peptide-fused ClyC (p-ClyC) is a novel and effective lysin to be against intracellular S. aureus and a potential antimicrobial agent for therapeutics against the pulmonary infections by S. aureus.