Structure-activity relationships of tetracyclines. I. Inhibition of cell division and protein and nucleic acid syntheses in Escherichia coli W

Evaluation of an indanyl ester of carbenicillin

Cultures of tetracycline-treated Staphylococcus aureus exhibited monophasic steady-state growth curves similar to that observed for tetracycline-treated Escherichia coli. Apparent growth rate constants of the respective drug-treated cultures showed the same formal dependence on drug concentration, which was linear at a low concentration but asymptotically approached zero at higher concentration levels and implied the saturation of a limited number of receptor sites engaged in microbial protein synthesis. The relative potency of tetracycline action of S. aureus/E. coli was 6.50:1 at 37.5°C and pH 7.05. This is attributed to relative differences in drug permeation and/or binding affinity for biophase receptors in the respective organisms. It is concluded from kinetic dependencies of growth inhibition of the cultures that tetracycline has the same mode of action on S. aureus and E. coli. It is bacteriostatic at concentrations below the minimal inhibitory concentration level but bactericidal at the higher concentration levels.

Microbial kinetics and dependencies of individual and combined antibiotic inhibitors of protein biosynthesis

The generation rate constants for the steady-state growth of antibiotic-inhibited Escherichia coli have the same formal dependency on concentration for deoxylincomycin, lincomycin (phase I), erythromycin, clindamycin, and U24729A. They may be kinetically classified as a group A, in which the first three compounds comprise a subgroup A(1) and the latter two a subgroup A(2). Generation rate constants initially decrease linearly with concentration but asymptotically approach zero at higher concentrations. With tetracycline or chloramphenicol, the generation rate decreases linearly with all concentrations, and these compounds may be kinetically classified as group B. Combining an antibiotic from group A with one from group B gives a response equal to that obtained with equivalent amounts of each antibiotic alone, and there are no significant effects from the order of antibiotic addition. However, combinations of an A(1) with an A(2) antibiotic are antagonistic, and there are significant effects from the order of addition. The dependencies of generation rate constants in the presence of these antibiotics can be rationalized by a receptor site model that considers varying degrees of the rate of drug transfer and drug inactivation in the organism.