RAPID AND ECONOMICAL METHOD FOR SPECIES IDENTIFICATION OF CLINICALLY SIGNIFICANT COAGULASE-NEGATIVE STAPHYLOCOCCI

Four methods for the species identification of coagulase-negative stap hylococci in the medical microbiology laboratory were compared with 44 4 consecutive isolates. The methods included (i) the reference method based on growth tests, (ii) API ID 32 Staph (bioMerieux), (iii) Staph- Zym (Rosco), and (iv) a rapid 4-h method developed in our laboratory ( UZA method). The last method is based on the detection within 4 h of e nzymatic activity of heavy bacterial suspensions in three substrate so lutions (nongrowth tests). For 16.5% of the isolates some supplementar y growth tests read after 24 h had to be added to the enzyme data for satisfactory identification. The reference method failed to identify f our isolates. Of the 440 isolates identified by the reference method, API ID 32 Staph, Staph-Zym, and the UZA method correctly identified 41 9 (95.2%), 429 (97.5%), and 430 (97.7%) and misidentified 8 (1.8%), 4 (0.9%), and 1 (0.2%), respectively. Staphylococcus epidermidis, S. hae molyticus, S. lugdunensis, S. schleiferi, and S. capitis were identifi ed with an accuracy of 98 to 100% by all the systems tested. S. capiti s subsp. ureolyticus was not recognized by the API ID 32 system becaus e the biochemical profiles for it are not yet included in the correspo nding database. Whereas API ID 32 identified all 13 S. warnerii isolat es, both Staph-Zym and the UZA method missed 2 of these. S. hominis wa s identified with the least accuracy by the API ID 32 system (26 of 39 isolates), whereas the UZA and Staph-Zym methods identified 36 of the isolates belonging to this species. The UZA method did not identify a ny of the S. cohnii, S. xylosus, S. lentus, and S. sciuri strains, sin ce it included no discriminatory tests for these species, because they are extremely rarely found in humans. Of all 440 isolates tested, the UZA method failed to identify 9 and misidentified 1 other. Eighty-one percent of the isolates were identified within 4 h and 97.7% were ide ntified after 24 h, at considerably less expense than by the API ID 32 Staph and Staph-Zym methods.