Abstract

The phenotypic study of the clinical strain Escherichia coli K18 showed that it is resistant to penicillin and amoxicillin-clavulanate, but susceptible to the combination of piperacillin-tazobactam and the cephalosporins 3rd generation and meropenem. The isolated β-lactamase, using ion-exchange chromatography on resin Mono-Q, gave a yield of 56%, a purification factor equal to 5.9, a molecular weight of approximately 24 KDa and a pI of 5.2. Clavulanic acid, tazobactam and sulbactam were competitive inhibitors with K_I and IC₅₀ far beyond the values of those of TEM-1. 13 molecules of different flavonoÏŠds, three phenolic acids (cafeic acid, ellagic acid and gallic acid) are tested for their ability to inhibit β-lactamase. The type of inhibition and K_Iare determined and the relationship between the structure and activity was established. The results showed that fisetin, flavone, quercetin, catechin and gossypin are non-competitive inhibitors. Myricetin, quercitrin, naringenin, morin, kaempferol and rutin are non-competitive inhibitors. The K_I of the most flavonoÏŠds tested are above 100 μM, which are 200 folds less effective than clavulanic acid (K_I = 0.5 µM). We can conclude that the position of OH in the structures of molecules has a major influence.

Key words: β-lactamase, Escherichia coli, β-lactam, clavulanic acid, flavonoids, phenolic acids.