Evaluation of the RapID ANA II and API ZYM systems for identification of Actinomyces species from clinical specimens

Abstract

Classification and identification of fermentative actinomycetes are labor-intensive and problematic. In this study, we evaluated the applicability and reliability of the RapID ANA II system (Innovative Diagnostic Systems, Inc., Atlanta, Ga.) and the discriminatory value of the API ZYM system (Societes Analytab Products Inc., La Balme Les Grottes, France) in the identification of Actinomyces-like bacteria by using conventional methods as a reference. Eighty-five strains, including 71 isolates from mixed anaerobic infections and 14 reference strains, were tested. The RapID ANA II system correctly identified all Actinomyces odontolyticus strains and 65% of Actinomyces israelii strains. All Arcanobacterium haemolyticum strains were misidentified as Actinomyces pyogenes. The most common isolates in the study were Actinomyces meyeri-like organisms, 84% of which, however, were aerotolerant. The identification of these aerotolerant strains thus remains unresolved and warrants further studies. New characteristics and changes to the conventional API ZYM enzyme profiles are suggested. The API ZYM enzyme profiles of A. odontolyticus and A. israelii were very similar, the only discriminating enzyme being alpha-fucosidase. In differentiation between A. pyogenes and Arcanobacterium haemolyticum, the production of beta-glucuronidase by the former and the production of acid phosphatase by the latter are suggested as new helpful characteristics for use in clinical laboratories. In summary, the RapID ANA II and API ZYM systems can be used as rapid preliminary methods in the identification of Actinomyces species but accurate identification requires supplementary conventional tests and gas-liquid chromatography.