The most widely used method for routine antibiotic susceptibility testing of
clinical isolates of bacteria is the paper-disc method. This has the advantage of
simplicity, but to obtain reliable results considerable care is required both in the
standardization of the procedure and in the interpretation of the zones of inhibition.
A new susceptibility test method is described in this report which retains the simplicity
of the paper-disc method but which enables organisms to be tested directly for
susceptibility to known concentrations of antibiotic in agar. Organisms may be
tested against a single concentration of antibiotic or, altematively, a range of concentrations
may be used to determine the minimal inhibitory concentration. The
method utilizes stable pre-prepared materials and is not appreciably more time consuming
than the conventional disc method.