Enzymatic reactions of Clostridium difficile in aerobic and anaerobic environments with the RapID-ANA II identification system.

The RapID-ANA II anaerobic identification system (Innovative Diagnostic Systems, Inc., Atlanta, Ga.) was used to determine whether the incubation environment affects enzyme detection. Twenty strains of Clostridium difficile were tested in aerobic, anaerobic, and low-CO2 anaerobic incubation environments. The percentages of enzymes detected in reactions with the following substrates were noted in the three incubation environments: phenylalanine-beta-naphthylamide, aerobic, 0%; anaerobic, 35%; low-CO2 anaerobic, 35%; arginine-beta-naphthylamide, aerobic, 5%; anaerobic, 55%; low-CO2 anaerobic, 75%; pyrrolidonyl-beta-naphthylamide, aerobic, 5%; anaerobic, 65%; low-CO2 anaerobic, 65%. When the aerobic incubation environment was compared with either the anaerobic or the low-CO2 anaerobic incubation environments, the results were statistically different with respect to enzyme detection in reactions with the substrates listed above. The results for the anaerobic and low-CO2 anaerobic environments were not statistically different. The study was repeated twice. Statistical comparisons between the three environments were consistent with the results presented above, with the following exceptions. The aerobic and the anaerobic environments were not different in a reaction with phenylalanine-beta-naphthylamide in one of the runs, and there was no significant difference between the three environments in a reaction with arginine-beta-naphthylamide in another run. These results suggest that some of the enzymes used in the identification of clinical anaerobes appear to be inactive in an environment containing oxygen.