Growth kinetics of respiratory pathogens after short exposures to ampicillin and erythromycin in vitro

The phenomenon of persistent suppression of bacterial growth (post-antibiotic effect, PAE) after short drug exposures was studied using ampicillin and erythromycin against Staphylococcus aureus , streptococci and Haemophilùs influenzae . A PAE of up to 4 and 6.7 h could be demonstrated for ampicillin and erythromycin, respectively. The PAE depended on the drug concentration and the duration of the drug exposure. Organisms in the PAE-phase were less susceptible to the bactericidal activity of ampicillin. The PAE was still demonstrated when the test culture had been stored on ice for 24 h. The PAE induced by erythromycin in vitro was also shown to persist in leukopenic mice. In normal mice PAE-phase organisms were more readily killed than non-exposed control organisms.