Investigating the biological activity and biofilm inhibition of purified Pichia kudriavzevii killer toxin (PkKt) against pathogenic bacterial as a promising substance for food preservation

Killer toxins (PkKT) produced by yeasts exhibit antimicrobial effects against pathogenic bacteria and fungi. This study aimed to extract, purify, and characterize the killer toxin from Pichia kudriavzevii killer toxin (PkKT) and evaluate its antimicrobial and anti-biofilm potential. PkKT was produced as a killer toxins and was purified through ammonium sulfate precipitation, ion exchange chromatography, and gel filtration. The purified PkKT showed a molecular weight of 36 kDa. Antimicrobial testing revealed significant inhibition against Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa, Klebsiella pneumoniae, Listeria monocytogenes, Acinetobacter baumannii, Escherichia coli, and Candida albicans using well diffusion assays. The minimum inhibitory concentration (MIC) ranged from 16-128 ?g/mL, while the sub-MIC was determined to be 8-64 ?g/mL depending on the pathogen. At sub-MIC levels, PkKT exhibited a 66-89% reduction of biofilm formation in all tested species. S. aureus, S. pyogenes, and A. baumannii showed the highest MIC of 128 and 64 ?g/mL sub-MIC, while E. coli and K. pneumoniae were most susceptible with MIC of 16 ?g/mL and sub-MIC of 8 ?g/mL. In conclusion, the purified PkKT toxin displayed broad-spectrum antimicrobial and anti-biofilm activities against common healthcare-associated pathogens. These findings reveal the potential of PkKT as a therapeutic agent to prevent or treat biofilm-associated infections.