Antimicrobial activity of the rationally modified peptide KK12 and its evaluation in a cooked chicken challenge model inoculated with Salmonella enterica serovar Typhimurium

A peptide from black soldier fly larvae, KGNSELEEAKKK, was subjected to structural modifications through cationic and hydrophobic residues. The modified peptide KWWSKLKKFWKK (KK12), which had a net charge of +6 and 41.67% hydrophobic residues with tryptophan substitution, was the most potent peptide against salmonellosis-involving serotypes, particularly Salmonella Typhimurium TISTR 292, with a minimum inhibitory concentration (MIC) value of 2 µM as indicated by a microdilution assay. Scanning electron microscopy and transmission electron microscopy showed morphological changes and membrane disintegration in the KK12-treated cells, accompanied by DNA leakage as monitored at 260 nm. Synchrotron-based Fourier-transform infrared spectroscopy indicated that KK12 induced modifications of intracellular targets. KK12 showed a hemolytic rate of < 5% up to 16 µM and maintained comparable viability of Vero and HepG2 cell lines relative to untreated controls at concentrations up to 36 and 18 µM, which was approximately 8, 18 and 9 times, respectively, higher than its MIC, implying its safety for food and pharmaceutical applications. KK12 reduced the bacterial count on chicken meat surface inoculated with S . Typhimurium TISTR 292 with the maximum reduction of 1.09 log colony forming units (CFU) observed at 1.6 nmol (2.71 µg). These results indicated that KK12 could be a potential candidate for Salmonella control.