Comparison of Minitek and conventional methods for the biochemical characterization of oral streptococci

Fifty-six strains of viridans streptococci were tested in the Minitek system (BBL Microbiology Systems, Cockeysville, Md.), and the results were compared with those obtained by conventional methods. An overall agreement of 98.9% was obtained when the Minitek tests were performed as follows. (i) All disks were incubated anaerobically for 48 h except for esculin and arginine, which required 5 to 7 days. (ii) The arginine disks were overlaid with 0.1 ml of sterile mineral oil even though incubated anaerobically. (iii) The Voges-Proskauer tests were performed under aerobic and anaerobic conditions. (iv) All tests for carbohydrate fermentation except for raffinose and salicin were read after the addition of 2 to 3 drops of 0.025% phenol red (pH 7.2). Of all the tests performed, only the fermentation of starch resulted in such poor agreement as to be considered unreliable. Results for inulin (unavailable in the Minitek system) were obtained by conventional methods.