Abstract: The method and apparatus for testing the susceptibility of bacteria to antibiotics described in the U.S. Pat. No. 3,832,532 and related patents are adapted for identifying various strains of bacteria by determining the light scatter indices (LSI) for a special group of antimicrobials, which have particularly significant characteristics with respect to identifying the strains of microorganisms, and analyzing them by a computer method, such as a quadratic discriminant function statistical technique, to identify the microorganisms to which the antimicrobials are applied. It has been found that 14 antimicrobial agents provide an extremely reliable identification and it is believed that the identifying group of agents could be reduced without sacrificing too much reliability. The agents preferably should be those which are not in common therapeutic use to avoid errors resulting from strains which have become immune to various therapeutically-utilized antibiotic agents.

Abstract: A flat sandwich composite plate of nested wedge-shaped sheets of highly transparent and gray neutral density filter glasses is enclosed in a frame. A bracket on the frame mounts it on the carriage of an optical instrument which measures the light scattering characteristics of a series of samples traversed on a carriage past a photometering station. A surface of the composite plate has a mat finish which scatters the light passing through it. The density and thickness of the filter glass are arranged to cover a predetermined range of light scatter corresponding to that caused by the range of samples which the optical instrument can accurately measure. An appended flat section of filter glass provides light scatter characteristics corresponding to an auxiliary sample characteristic. The transmittance of the appended section is adjusted by a movable leaf and notched adjusting segments. The mat surface is obtained by frosting a surface of the filter glass by blasting or grinding with 9 micron grit.