Author(s): Ligozzi M, Bernini C, Bonora MG, De Fatima M, Zuliani J,
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Abstract A study was conducted to evaluate the new VITEK 2 system (bioMérieux) for identification and antibiotic susceptibility testing of gram-positive cocci. Clinical isolates of Staphylococcus aureus (n = 100), coagulase-negative staphylococci (CNS) (n = 100), Enterococcus spp. (n = 89), Streptococcus agalactiae (n = 29), and Streptococcus pneumoniae (n = 66) were examined with the ID-GPC identification card and with the AST-P515 (for staphylococci), AST-P516 (for enterococci and S. agalactiae) and AST-P506 (for pneumococci) susceptibility cards. The identification comparison methods were the API Staph for staphylococci and the API 20 Strep for streptococci and enterococci; for antimicrobial susceptibility testing, the agar dilution method according to the procedure of the National Committee for Clinical Laboratory Standards (NCCLS) was used. The VITEK 2 system correctly identified to the species level (only one choice or after simple supplementary tests) 99\% of S. aureus, 96.5\% of S. agalactiae, 96.9\% of S. pneumoniae, 92.7\% of Enterococcus faecalis, 91.3\% of Staphylococcus haemolyticus, and 88\% of Staphylococcus epidermidis but was least able to identify Enterococcus faecium (71.4\% correct). More than 90\% of gram-positive cocci were identified within 3 h. According to the NCCLS breakpoints, antimicrobial susceptibility testing with the VITEK 2 system gave 96\% correct category agreement, 0.82\% very major errors, 0.17\% major errors, and 2.7\% minor errors. Antimicrobial susceptibility testing showed category agreement from 94 to 100\% for S. aureus, from 90 to 100\% for CNS, from 91 to 100\% for enterococci, from 96 to 100\% for S. agalactiae, and from 91 to 100\% for S. pneumoniae. Microorganism-antibiotic combinations that gave very major errors were CNS-erythromycin, CNS-oxacillin, enterococci-teicoplanin, and enterococci-high-concentration gentamicin. Major errors were observed for CNS-oxacillin and S. agalactiae-tetracycline combinations. In conclusion the results of this study indicate that the VITEK 2 system represents an accurate and acceptable means for performing identification and antibiotic susceptibility tests with medically relevant gram-positive cocci.
This article was published in J Clin Microbiol
and referenced in Journal of Nanomedicine & Nanotechnology