Examination of model enzyme and penetration systems in relation to antibacterial activity.

Recent work has shown that the activity of cephalosporins in inhibiting exocellular DD-peptidases from Streptomyces R61 and Actinomadura R39 are, at best, only poorly related to minimum inhibitory concentrations against pathogenic isolates. Taking into account the rate at which cephalosporins diffuse through porin channels, such as exist in certain Gram-negative organisms, does not help in establishing a relationship between MIC data and the kinetic data on the model enzymes. Most published cell wall permeability studies, the porin ones being a principal exception, have not examined long enough series of structurally related compounds to establish property-activity relationships.