In vitro studies with mecillinam on Escherichia coli and Pseudomonas aeruginosa.

The ability of a beta-lactam antibiotic to inhibit the growth of Gram-negative bacteria depends on three main properties: ting sites in the bacterial cell; the ability to penetrate through the outer layers of the bacterial envelope to these sites; and the ability to resist destruction by beta-lactamases that may be encountered on the way to the target. This article describes the properties of mecillinam with respect to the last two of these properties. Although able to hydrolyse mecillinam under some conditions, the beta-lactamases present in many Gram-negative species are unlikely to be very effective at protecting the bacteria in vivo because of their relatively low affinity for this penicillin and the good penetrative properties of the antibiotic.