Biochemical identification of bacteria by replicator methods on agar plates.
Biochemical tests commonly used for the identification of bacteria were adapted to a replicator technique using agar plates. As many as 48 organisms could be tested on one 10 cm square Petri dish. A new indicator, 2-(2,4-dinitrophenylazo)-l-naphthol-3,6-disulphonic acid disodium salt made it possible to investigate Gram-positive as well as Gram-negative organisms. For certain tests, such as citrate, DNAase, gelatin or lipase, a standard method using agar was already available. For others the usual test in liquid medium had to be adapted to solid medium. All such tests were compared with the API 20E system or with a conventional test and the results of the replicator tests showed a high correlation with those of other systems. For Gram-negative rods the corrected error rates (a measure of reproducibility) of 22 tests were 1% or less, for the remaining 9 tests the figure ranged between 1.5% and 4.8%. For Gram-positive cocci the corrected error rates of 21 tests were 1% or less and for the remaining 10 the figure ranged between 2% and 11%. The plates could be kept at 4-6 degrees C for 2 wk without appreciable loss of activity. The duration of incubation affected the results only marginally. This system has considerable advantages. Control organisms can be included in every run. As the cost in time and reagents for individual tests is much reduced, a larger number of tests can be carried out and this provides better identification. As Gram-positive organisms will grow on these media, it would be possible to speciate them in a more detailed fashion than is usually done now.
D000362:Agar; D001419:Bacteria / Q000145:classification; D001431:Bacteriological Techniques; D003470:Culture Media
D003470:Culture Media; D000362:Agar