Identification of Legionella pneumophila with commercially available immunofluorescence test.

The Table shows results obtained with 24 strains of ONPG negative H influenzae. Us- ing the heavy inoculum, results were identi- cal for tube and API-IOS strips, except for one strain that was positive for ornithine de- carboxylase in the tube but negative on the strip (strain 8).The Table clearly shows the inadequacy of the smaller inoculum.The numbers of positive tube tests for urease, or- nithine decarboxylase, and indole formation were 18, 11, and 16, respectively, for the heavy inoculum compared with 16, 1, and 12 for the smaller inoculum.Inoculum size seems to be especially critical for detection of ornithine decarboxylase.A series of replicate tests showed that reproducible results could be obtained with either tube or API- lOS strips with the heavy inoculum, but all three tests gave variable results with smaller inocula.A series of viable counts performed on inocula prepared according to the API recommendations gave values ranging from 1 3 x 10i to 30 x 10 colony forming units, depending on colony size.We found that a minimum inoculum size of 1-25 x 106 colony forming units is required for reliable detection of urease and indole formation and 1-25 x 10 for omithine decarboxylase production.