Assessment of enzyme detection tests useful in identification of campylobacteria

Twenty-one type or other reference strains, each representing a different Campylobacter, Helicobacter, or Arcobacter taxon, and a reference strain of Staphylococcus aureus were used to assess the reproducibility of nine enzyme detection tests used in the identification of campylobacters. For five of the tests (alkaline phosphatase, DNase, and H2S production, indoxyl acetate hydrolysis, and nitrate reduction), more than one procedure was employed to determine the most suitable method. Alkaline phosphatase test results were better defined and more reproducible if read after 1 h of incubation. Detection of DNase was fully reproducible with each method (except with Helicobacter pylori), but reactions were generally weaker than those of other DNase-producing organisms. Both procedures for determining H2S production were irreproducible for the same strains. The reproducibility of indoxyl acetate hydrolysis was improved by using disks impregnated with 25 microliters of substrate. Reduction of nitrate was best determined by Cook's plate method. Results for the other tests examined (catalase, oxidase, and urease production and hippurate hydrolysis) were both pertinent and fully reproducible for all strains.