A Standardized Disk Method for Antibiotic Susceptibility Testing for Anaerobes; Four Years of Antibiotic Data

Abstract

In vitro antibiotic susceptibility testing of aerobes and facultative bacteria has been a service provided by the clinical laboratory since the 1940’s. However, little effort was made to standardize susceptibility tests until 1966 when investigators at the University of Washington in Seattle developed a technique which became known as the Kirby-Bauer technique. The standardized technique employed Mueller-Hinton agar as the test medium and a single high-content disk with a standard concentration of antimicrobic; adjusting the density of the inoculum before inoculating the plate, and the development of interpretive standards based on growth inhibition zone diameters around the disk. These interpretive standards were developed by determining the relationship between zone diameters and the minimal inhibitory concentrations (MIC) and relating this information to the achievable serum levels of the antibiotic after the usual dose was administered to the patient. The Kirby-Bauer technique has been the generally accepted technique throughout the United States for testing rapidly growing aerobes and facultative bacteria.