Potential Inhibitory Effect of the Peptide Melittin Purified from Apis mellifera Venom on CTX-M-Type Extended-Spectrum β-Lactamases of Escherichia coli

Background. Extended-spectrum β-lactamases (ESBLs) hydrolyze nearly all β-lactam antibiotics, affecting one of the most important groups of antimicrobials used in Gram-negative infections. Among them, CTX-M is the most widespread type of ESBL. This study aimed to evaluate the hydrolytic activity of CTX-M-type ESBLs following exposure to the antimicrobial peptide Melittin. Methods. Melittin was purified from Apis mellifera venom through ultrafiltration and characterized by SDS-PAGE. The minimum inhibitory concentration (MIC) of Melittin against ESBL-producing E. coli was determined by the broth microdilution method. The inhibition of ESBL’s hydrolytic activity following exposure to sub-MIC doses of Melittin was quantified using a kinetic assay based on hydrolyzed nitrocefin. Additionally, the effect of Melittin on the expression of the bla_CTX-M gene was evaluated via RT-PCR. Results. The peptide fraction of Apitoxin smaller than 10 kDa exhibited a protein band corresponding to Melittin, devoid of higher molecular weight proteins. The MIC of Melittin ranged from 50 to 80 µg/mL. Exposure to Melittin at sub-MIC doses significantly inhibited ESBL hydrolytic activity, reducing it by up to 67%. However, the transcription of the bla_CTX-M gene in the presence of Melittin revealed no significant changes. Conclusions. Melittin is able to inhibit ESBL’s hydrolytic activity but not bla_CTX-M transcription possibly indicating an effect at the translational or post-translational level.