Comparative antibacterial efficacy of cationic antimicrobial peptide- bactenecin and green synthesized silver nanoparticles against multidrug resistant bacteria

Emerging antimicrobial resistance (AMR) against common foodborne pathogens, has been observed in an increasing trend recently. The situation becomes grave when multi-drug resistance is reported toward the antibiotics of front-line therapy. Therefore, novel alternate therapeutics such as cationic antimicrobial peptides (AMPs), nanoparticles, etc., have attracted considerable attention to combat AMR. This study evaluated the in vivo antimicrobial efficacy of previously characterized bactenecin and green synthesized silver nanoparticles (AgNPs) against multidrug-resistant field isolates of Listeria monocytogenes and Staphylococcus aureus originating from poultry meat. To assess the in vivo antimicrobial efficacy, the Galleria mellonella (Wax moth) larval model is used as a substitute for traditional murine in vivo models which have ethical, financial, and logistical limitations. The micro broth dilution method was used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of bactenecin and AgNPs against both pathogens. The AgNPs and bactenecin showed 64 and 128 μM MBC against MDR-L. monocytogenes and MDR-S. aureus, respectively. Further, to assess the in vivo antimicrobial efficacy of these therapeutic candidates against both bacteria, an LD50 assessment, survival rate, bacterial count, melanization rate, hemocyte enumeration, and cytotoxicity assays were carried out in the G. mellonella larvae model. Overall, the infected G. mellonella larvae treated with either bactenecin or AgNPs revealed an improved survival rate, immunomodulatory effect, and reduced bacterial counts thus leading to a lesser degree of bacterial-induced cytotoxicity. However, the current study demonstrated that AgNPs was more efficacious in terms of MBC value, inducing hemocyte count and providing a steady decline in bacterial-induced cytotoxicity as compared to bactenecin, whereas, bactenecin exhibited a better survival rate in MDR-L. monocytogenes infected larvae. To conclude, the results suggest that both bactenecin and AgNPs as alternate therapeutic candidates showed an effective antimicrobial effect on MDR-L. monocytogenes and MDR-S. aureus of poultry origin. However, further investigation of these therapeutic candidates against the targeted pathogens in appropriate animal models is recommended before its application in the target host.