Summary: This study investigated the ability of anaerobic periodontal bacteria to inactivate and resist killing by antimicrobial peptides through production of extracellular proteases. Antibacterial activities of peptides were assessed in a double-layer agarose diffusion assay, and MICs and MBCs were determined in broth microdilution assays. Culture supernates of and spp. inactivated mastoparan, magainin II and cecropin B whilst Gram-positive oral supragingival bacteria had no effect. Inactivation was prevented by protease inhibitors and was unaffected by 45% human serum. Purified proteases from the periodontopathogen inactivated peptides [cecropin B, brevinin, CAMEL (cecropin A 1–7 + melittin 2–9), mastoparan] as would be predicted from the amino acid sequences of the peptides and the known bond specificities of these Arg-x and Lys-x enzymes. MALDI-TOF MS revealed that inactivation of cecropin B by protease was due to specific cleavage of the molecule. Inactivation of cecropin B by proteases took 10–15 min. Paradoxically, MICs of cecropin B against and were low, while was resistant, suggesting that production of proteases alone is insufficient to protect and from the action of antimicrobial peptides. Thus, antimicrobial peptides could be developed as therapeutic agents targeted against specific periodontal pathogens.


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