Rapid and economical method for species identification of clinically significant coagulase-negative staphylococci

Abstract

Four methods for the species identification of coagulase-negative staphylococci in the medical microbiology laboratory were compared with 444 consecutive isolates. The methods included (i) the reference method based on growth tests, (ii) API ID 32 Staph (bioMérieux), (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 enzymatic activity of heavy bacterial suspensions in three substrate solutions (nongrowth tests). For 16.5% of the isolates some supplementary growth tests read after 24 h had to be added to the enzyme data for satisfactory identification. The reference method failed to identify four isolates. Of the 440 isolates identified by the reference method, API ID 32 Staph, Staph-Zym, and the UZA method correctly identified 419 (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. haemolyticus, S. lugdunensis, S. schleiferi, and S. capitis were identified with an accuracy of 98 to 100% by all the systems tested. S. capitis subsp. ureolyticus was not recognized by the API ID 32 system because the biochemical profiles for it are not yet included in the corresponding database. Whereas API ID 32 identified all 13 S. warneri isolates, both Staph-Zym and the UZA method missed 2 of these. S. hominis was 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 any of the S. cohnii, S. xylosus, S. lentus, and S. sciuri strains, since 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 identified after 24 h, at considerably less expense than by the API ID 32 Staph and Staph-Zym methods.

Comparison of a commercialized phenotyping system, antimicrobial susceptibility testing, and tuf gene sequence-based genotyping for species-level identification of coagulase-negative staphylococci isolated from cases of bovine mastitis

“…Zym™ and the need for supplementary tests in relation to reference strains (Watts and 220 Washburn, 1991; Ieven et al, 1995;Burriel and Scott, 1997). We used the same S. 221 chromogenes reference strain as Burriel and Scott (1997), and in both studies Staph-Zym™ 222 was unable to give a name (No match) to that strain.…”

Cytidine deamination assay to differentiate Staphylococcus aureus from other staphylococci

“…In the second identification step all the 249 staphylococci were identified with the ID 32 One of the 16 clumping factor-negative S. aureus isolates gave negative reaction with the kit, and two of them gave nonspecific agglutinations. Gram-positive cocci with unpigmented colonies with morphology compatible with that of staphylococci and which were catalase-positive but clumping factor-negative were further identified to the species level using the ID 32 Staph system (Ieven et al 1995).…”

Glyceraldehyde-3-Phosphate Dehydrogenase-Encoding Gene as a Useful Taxonomic Tool for Staphylococcus spp

“…However, phenotypic methods did not allow a correct CI-2 identification. It is known that S. hominis, which is one of the most common species after S. epidermidis and S. haemolyticus, is usually identified with a low accuracy by the API ID32 system (10,11,27).…”

“…Several methods of identifying Staphylococcus spp. have been proposed, including those that detect traditional phenotypic properties, which are available in miniaturized form for automation and convenience (2,10,21,34), and gas-liquid chromatography analysis of cellular fatty acids (31). However, many isolates are still poorly identified by these methods, and supplementary test are often required for a complete identification.…”