GRADIENT PLATE BIOASSAY FOR TYROTHRICIN AND ITS APPLICATION TO DENTIFRICES.
A bioassay for tyrothricin, based on a procedure used by Szybalski in bacterial resistance studies, was developed. Replacement of the tube dilution assay with this procedure represented economy in time and equipment, with a resultant increase in productivity. The procedure involved preparation of special agar plates which provided graded concentrations of tyrothricin along a horizontal axis. A culture dish was inclined, and a base layer of agar, without antibiotic, was poured to cover the bottom of the dish and allowed to harden. A second layer of agar, containing 1 ppm of tyrothricin, was poured and allowed to harden with the dish in a level position. Diffusion of the antibiotic from the top layer into the bottom layer yielded a concentration gradient. A third thin layer of agar seeded with Streptococcus faecalis was poured on the surface. After incubation, a bacterial growth front, representing the minimal effective concentration (MEC), developed. The MEC is expressed as distance (in millimeters) from the edge of the plate. Unknowns were directly related to a standard preparation for calculation of tyrothricin concentration.
D000362:Agar; D000900:Anti-Bacterial Agents; D000904:Antibiotics, Antitubercular; D001681:Biological Assay; D003802:Dentifrices; D013293:Enterococcus faecalis; D012106:Research; D014449:Tyrothricin
D000900:Anti-Bacterial Agents; D000904:Antibiotics, Antitubercular; D003802:Dentifrices; D014449:Tyrothricin; D000362:Agar
ANTIBIOTICS; BIOLOGICAL ASSAY; DENTIFRICES; EXPERIMENTAL LAB STUDY; STREPTOCOCCUS FAECALIS