Spectrophotometric Detection of Beta-Lactamase Inhibition by Plant Extracts

Background: Antibiotic-resistant bacteria have been spreading with increasing frequency over the past several decades. The decreasing effectiveness of therapies in treating bacterial resistance, due to the production of beta-lactamase (EC.3.5.2.6), has led to combining beta-lactamase inhibitors with commonly used beta-lactam antibiotics. Phytochemical compounds produced by plants have varied biological properties such as antioxidant, antimicrobial, antidiabetic, anti-inflammatory, anticancer, antihypertensive and others. Polyphenolics, flavonoids, coumarins, alkaloids, tannins, steroids and terpenoids are the main phytochemicals found in plants extracts. This study aims to assess the inhibitory activity of Annona senegalensis Pers., Terminalia superba Engl. & Diels, Ipomoea batatas Lam., and Psidium guajava L. against a Bacillus cereus beta-lactamase and four beta-lactamases extracted from clinical isolates of Escherichia coli. Methods: Beta-lactamase inhibition was measured using a spectrophotometric assay with benzylpenicillin as the substrate, by a modified acidimetric method. Clavulanic acid was used as the standard beta-lactamase inhibitor. Subsequently, the inhibition of the hydrolysis of other commonly used beta-lactam antibiotics was assessed using a UV spectrophotometric method. Results: Among the tested extracts, Ipomoea batatas showed no effect on the beta-lactamases, whereas Terminalia superba and Annona senegalensis exhibited inhibitory activity against all the beta-lactamases. Psidium guajava inhibited two of the five tested enzymes. The highest percentage of inhibition was observed with Terminalia superba on the beta-lactamase of Bacillus cereus, reaching 75.73%. Regarding the combination of beta-lactam antibiotics with plant extracts, the combination of Terminalia superba and ceftriaxone showed the highest inhibition, with a percentage of 64.90%. The combination of Annona senegalensis and ceftazidime was the least effective, with an inhibition rate of only 12.95%. Conclusion: Two of the tested ethanolic plant extracts showed interesting beta-lactamase inhibitory effects and could contribute to the development of more effective therapies against beta-lactamase-producing bacteria by combining natural inhibitors from plants with existing beta-lactam antibiotics.