A new Kunitz trypsin inhibitor from Erythrina poeppigiana exhibits antimicrobial and antibiofilm properties against bacteria.

Erythrina poeppigiana belongs to Fabaceae family (subfamily Papillionoideae) and is commonly found in tropical and subtropical regions in Brazil. Herein, we described the purification and characterization of a new Kunitz-type inhibitor, obtained from E. poeppigiana seeds (EpTI). EpTI is composed by three isoforms of identical amino-terminal sequences with a molecular weight ranging from 17 to 20 kDa. The physicochemical features showed by EpTI are common to Kunitz inhibitors, including the dissociation constant (13.1 nM), stability against thermal (37-100 °C) and pH (2-10) ranging, and the presence of disulfide bonds stabilizing its reactive site. Furthermore, we investigated the antimicrobial, anti-adhesion, and anti-biofilm properties of EpTI against Gram-positive and negative bacteria. The inhibitor showed antimicrobial activity with a minimum inhibitory concentration (MIC, 5-10 µM) and minimum bactericidal concentration (MBC) of 10 µM for Enterobacter aerogenes, Enterobacter cloacae, Klebsiella pneumoniae, Staphylococcus aureus, and Staphylococcus haemolyticus. The combination of EpTI with ciprofloxacin showed a marked synergistic effect, reducing the antibiotic concentration by 150%. The increase in crystal violet uptake for S. aureus and K. pneumoniae strains was approximately 30% and 50%, respectively, suggesting that the bacteria plasma membrane is targeted by EpTI. Treatment with EpTI at 1x and 10 x MIC significantly reduced the biofilm formation and prompted the disruption of a mature biofilm. At MIC/2, EpTI decreased the bacterial adhesion to polystyrene surface within 2 h. Finally, EpTI showed low toxicity in animal model Galleria mellonella. Given its antimicrobial and anti-biofilm properties, the EpTI sequence might be used to design novel drug prototypes.