Antibacterial effects assessment on some livestock pathogens, thermal stability and proposing a probable reason for different levels of activity of thanatin.

There is a continuing need to prevent the increasing use of common antibiotic and find the replacement to combat the drug/antibiotic resistant bacteria such as antimicrobial peptides (AMPs) such as thanatin peptide. In this study, recombinant thanatin peptide was expressed in the HEK293 cell line. Then the antimicrobial properties of this peptide on some poultry and farm animal's pathogen strains were assessed. The thermal-stability of thanatin was predicted in various temperatures through in silico analysis. Afterwards, according to Minimum Inhibitory Concentration (MIC) results, Escherichia coli and Pseudomonas aeruginosa were chosen to test the hypothesis of LptA/LptD-thanatin interaction, computationally. Relative amino acid sequences and crystallography structures were retrieved and missed tertiary structures were predicted. The interaction of thanatin with LptA and LptD of Escherichia coli and Pseudomonas aeruginosa were analyzed subsequently. The antibacterial activity of thanatin peptide was evaluated between 6.25 and 100 μg/mL using minimum inhibitory concentration. Also, the amounts of minimum bactericidal concentrations (MBC) were between 12.5 and 200 μg/mL. The bioinformatics analysis followed by the in vitro assessment, demonstrated that thanatin would be thermally stable in the body temperature of poultry and farm animals. Thanatin could penetrate to the outer membrane domain of LptD in Escherichia coli and it could block the transition path of this protein while the entrance of LptD in Pseudomonas aeruginosa was blocked for thanatin by extra residues in comparison with Escherichia coli LptD. In addition, the quality of interaction, with regard to the number and distance of interactions which leads to higher binding energy for thanatin and LptD of Escherichia coli was much better than Pseudomonas aeruginosa. But the site and quality of interaction for thanatin and LptA was almost the same for Escherichia coli and Pseudomonas aeruginosa. Accordingly, thanatin can prevent the assembly of LptA periplasmic bridge in both pathogens. The antibacterial and thermal stability of the thanatin peptide suggested that thanatin peptide might serve as a natural alternative instead of common antibiotics in the veterinary medicine. The outcome of this in silico study supports the MIC results. Therefore, a probable reason for different level of activity of thanatin against Escherichia coli and Pseudomonas aeruginosa might be the quality of LptA/LptD-thanatin interaction.