A Simple Method for Determining Bacterial Susceptibility to Aminoglycosides

A method is described of determining the susceptibility of enterobacteria to four amino-glycosides by means of an antibiotic diffusion method. The results are expressed as the minimal inhibitory concentration (MIC) of antibiotic and were compared with those obtained by a method that involved titration in agar plates and the use of a multi-point in-oculator. A statistical analysis showed that the diffusion method gave accurate reproducible results.

The antibiotic can be incorporated into paper disks, paper strips or agar ditches and the calculation converting the measured zones of inhibition to MIC values is easily performed. The appropriate equation is derived from another-obtained from observations on a single strain of known sensitivity-describing the diffusion of the antibiotic from the reservoir.