The Post Antibiotic Effect
The standard method for measuring in vitro antimicrobial activity is by determining the minimum inhibitory and bactericidal concentration (MIC and MBC). In these tests exposure of bacteria to a constant concentration of drug can differ significantly from the in vivo situation in which bacteria are usually exposed to fluctuating drug concentrations. The suppression of microbial growth that persists alter antimicrobial exposure has been ob- served since the early days of antimi- crobial chemotherapy. For example, studies in the 1940s demonstrated that staphylococci did not resume normal growth for I to 3 hr following only a 5 to 30 min exposure to penicillin G (1). However, it was not until the mid-1970s that persistent suppression of bacterial growth was studied with antimicrobial agents developed after penicillin and with gram-negative ba- cilli. Over the past 15 yr, persistent suppression of bacterial growth has been observed with a wide variety of bacteria and yeasts (2). We have used the term postantibiotic effect (PAE) to describe this phenomenon, since it emphasizes that the effect results from previous antimicrobial exposure.