Combined antibacterial activity of amoxicillin with clavulanic acid against ampicillin-resistant strains

Abstract

Strains of bacteria resistant to .beta.-lactam antibiotics are increasing in number and are becoming troublesome in clinical medicine. The in vitro antibacterial activity of amoxicillin combined with clavulanic acid was determined on selected ampicillin-resistant clinical isolates. Synergistic effects were produced by amoxicillin with clavulanic acid against ampicillin-resistant strains of Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, P. vulgaris and Bacteroides fragilis. Inhibition of the .beta.-lactamases produced by the ampicillin-resistant strains was confirmed, especially against the penicillinases mediated by the R factor and the cephalosporinases produced by P. vulgaris and B. fragilis. The inhibitory effect of clavulanic acid against .beta.-lactamases was irreversible because of the high affinity of clavulanic acid to the enzymes.