Accuracy and reproducibility of a four-hour method for anaerobe identification

Abstract

In this study, we evaluated the ability of a 4-h enzyme assay kit system, the RapID ANA method (Innovative Diagnostic Systems, Inc., Atlanta, Ga.) to accurately and reproducibly identify a spectrum of clinically significant anaerobic bacteria in two separate institutions. Additional tests were performed as required. Of a total of 188 organisms tested at Hershey Medical Center (HMC), 86.2% were correctly identified to species level without additional tests, 5.9% required extra tests for correct identification, and 8.0% were misidentified. Of 53 strains tested at Johns Hopkins Hospital (JHH), 52.8% were correctly identified without extra tests, 28.3% required extra tests for correct identification, and 18.9% were misidentified. Of 21 organisms tested at both institutions, those tested at JHH required additional tests for correct identification in 38.1% of cases, compared with 9.5% at HMC. Misidentification rates were identical (9.5%) in both centers. Of strains tested at HMC only, 86.8% were correctly identified without extra tests, 5.4% were identified with additional tests, and 7.8% were misidentified: corresponding data for JHH were 53.1, 21.9, and 25.0%, respectively. Of 53 strains tested in triplicate at JHH, 56.7% yielded the same result on each occasion, 37.7% were identical in two of three tests, and 5.7% gave different results on each of three occasions. Discrepancies between identification rates at HMC and JHH may be explained by differences in species tested (more commonly encountered species were tested at HMC) and interpretation of reactions by the two different readers. The RapID ANA method has the potential for rapid identification of clinically isolated anaerobes; however, accuracy and reproducibility may vary as a function of the specific laboratory setting.

Evaluation of the RapID-ANA system for identification of anaerobic bacteria of veterinary origin

“…Previously published evaluations of the RapID-ANA system have reported that some of the color reactions were difficult to interpret, thereby giving equivocal results (2,11). We also found that the clarity of the reactions varied with tests and the reactivity of a specific organism.…”

“…to minimize variability due to personnel. Appelbaum and co-workers (2) reported test discrepancies when 21 strains were tested separately by two laboratories and a lack of reproducibility in triplicate tests at the same laboratory. They attributed these errors to either product deficiencies or problems in interpretation of test reactions.…”

“…RapID-ANA system. The RapID-ANA system is a qualitative micromethod for anaerobe identification that has previously been described in detail (2,11). Inoculation, 4 h of incubation in a 35°C air incubator, and interpretation of the RapID-ANA tests were performed according to the instructions of the manufacturer.…”

“…Six Fusobacterium russii strains were tested. One strain was correctly identified at the genus level, while five strains were incorrectly identified as Bacteroides capillosus (2), Bacteroides ureolyticus, C. clostridiiforme, or Bacteroides sp. (2).…”

“…The accuracy and reproducibility of the RapID-ANA system (Innovative Diagnostic Systems, Inc., Atlanta, Ga.) for the identification of anaerobes of human origin has been evaluated (2,11). However, the usefulness of the RapID-ANA method for the identification of clinically significant anaerobes of veterinary origin has not been established.…”