Disk diffusion bioassays for the detection of antibiotic activity in body fluids: applications for the Pneumonia Etiology Research for Child Health project.

To draw inferences about the putative etiologic agents of severe pneumonia, the Pneumonia Etiology Research for Child Health (PERCH) project must be able to objectively assess antibiotic pretreatment in enrolled participants. This review is focused on the disk diffusion bioassay, a simple laboratory method to assess recent antibiotic treatment. In this method, a sensitive indicator organism is used to detect antimicrobial activity in body fluid specimens that have been inoculated on a filter paper disk and placed on agar growth medium. We reviewed and present several variations on the disk diffusion method as applied to serum or urine, including specimen handling, choice of indicator organism and medium, and incubation steps. Although there are limitations to the disk diffusion method, its low cost, ease of use, and ability to broadly detect antibiotic pretreatment make it an appealing method for epidemiologic studies such as PERCH.