Rapid determination of antibiotic susceptibility by a disc diffusion test for urgent clinical situations.

Employing the PDM method, disc diffusion antibiotic susceptibility tests were read after 4 and 8 h and compared to traditional readings after 18 h. Four hours of incubation was not found suitable. After 8 h of incubation, all the 74 strains tested showed visible growth and more than 75% of the readings fell in the same sensitivity groups. Nearly all the discrepancies observed could be classified as minor, and reading the plates after 8 h of incubation should be considered as a valuable alternative when the clinical need for rapid information is obvious.