A set of bacterial strains for evaluation of beta-lactamase-stability of beta-lactam antibiotics.

A set of bacterial strains composed of nine bacterial groups, with each made up of three or four strains, was used to estimate the stability of beta-lactam antibiotics to nine types of beta-lactamases from Gram-negative bacteria. The strains in the same group produced the same kind of enzyme constitutively, but the enzyme activity achieved in the bacterial cell differed with different strains. The difference in antibacterial activity of each antibiotic on the strains of each group, easily measured by a simple plate technique, permits an estimation of its relative stability to each beta-lactamase. This method was applied to thirteen beta-lactam antibiotics including seven new ones.