Abstract: Growth inhibition assays for both microorganisms and mammalian cells are performed by incubating the microorganisms or cells in a growth medium in the presence of resazurin and a suspected growth inhibiting agent. By observing a color change accompanied by the reduction of resazurin to resorfurin, continued cell viability can be determined. The present invention reduces system errors by inhibiting the autoreduction of resazurin by the growth media by incorporating suitable redox stabilizing agents in the medium. In a preferred embodiment the poising agent is potassium ferrocyanide, ferric salt or ferricinium and the medium is maintained at a potential from about +0.3 volts to about +0.45 volts. A second poising agent can be used to inhibit the reduction of resorfin to dihydroresorfin. Preferred second poising agents are methylene blue, toluidine blue, azure I and gallocyanide in amounts to maintain the potential of the growth medium above -0.1 volts.

Abstract: A microprocessor based apparatus and method for recording antimicrobic susceptibility data and biotype data. Manual data entry means in the form of two separate arrays of switches are provided for entering susceptibility data from microdilution test panels and a biochemical identification panels. An LED array is provided in a test panel housing on the front panel of the instrument cabinet in which the system is housed for feedback of data entry under microprocessor control. A microprocessor system records the entered well coordinated data for the microdilution test panel wells and the biochemical identification panel wells and converts the entered data into a printout of the minimum inhibitory concentration (MIC) of antimicrobics in the MIC test panel and a probable identification of the unknown microorganism. A multicopy form is provided for the printout from a printer functioning under microprocessor control.