The Papain Inhibitor (SPI) of Streptomyces mobaraensis Inhibits Bacterial Cysteine Proteases and Is an Antagonist of Bacterial Growth

A novel papain inhibitory protein (SPI) fromStreptomyces mobaraensiswas studied to measure its inhibitory effect on bacterial cysteine protease activity (Staphylococcus aureusSspB) and culture supernatants (Porphyromonas gingivalis,Bacillus anthracis). Further, growth ofBacillus anthracis,Staphylococcus aureus,Pseudomonas aeruginosa, andVibrio choleraewas completely inhibited by 10 μM SPI. At this concentration of SPI, no cytotoxicity was observed. We conclude that SPI inhibits bacterial virulence factors and has the potential to become a novel therapeutic treatment against a range of unrelated pathogenic bacteria.