Decreased bactericidal activity during the period of the postantibiotic effect.

Standard and clinical strains of Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae were subjected to continuous exposure to beta-lactams and aminoglycosides during the postantibiotic effect phase induced by rifampicin or erythromycin (for S. aureus). A significant inhibition of bactericidal activity by these agents during the PAE period was observed. The degree of inhibition was dependent both on the class of antimicrobial agent (beta-lactams > aminoglycosides) and the microorganism (Gram-negative bacilli > S. aureus).