Antimicrobial peptides (AMPs) are a diverse group of molecules which play an important role in the innate immune response. Bovine NK-lysins, a type of
AMP, have been predominantly found in the granules of cytotoxic T-lymphocytes and NK-cells. Bovine
NK-lysin-derived
peptides demonstrate antimicrobial activity against various bacterial pathogens, including several involved in
bovine respiratory disease complex (BRDC) in cattle; however, such studies are yet to be performed with one important contributor to the BRDC, Mycoplasma bovis. Therefore, the goal of this study was to assess the antimicrobial activity of bovine
NK-lysin-derived
peptides on M. bovis. Thirty-mer synthetic
peptides corresponding to the functional region helices 2 and 3 of bovine NK-lysins NK1, NK2A, NK2B, and NK2C were evaluated for killing activity on M. bovis isolates. Among four
peptides, NK2A and NK2C showed the highest antimicrobial activity against the M. bovis isolates tested. All four
NK-lysin peptides induced rapid plasma membrane depolarization in M. bovis at two concentrations tested. However, based on
propidium iodide uptake, only NK2A and NK2C appeared capable of causing structural damage to M. bovis plasma membrane. Confocal microscopy, flow cytometry, and transmission electron microscopy further suggested
NK-lysin-induced damage to the plasma membrane. Taken together, the findings in this study suggest that plasma membrane depolarization alone was insufficient to induce lethality, but disruption/permeabilization of the M. bovis plasma membrane was the cause of lethality.