Evaluation of the VITEK 2 System for Identification and Antimicrobial Susceptibility Testing of Medically Relevant Gram-Positive Cocci

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), coagulasenegative 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. agalactiaetetracycline 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.Automation in clinical microbiology is still in a very early stage of development compared with the level of automation that has been achieved in clinical chemistry, hematology, and immunology laboratories.In the last 20 years, a variety of automated systems for the identification and antimicrobial susceptibility testing (AST) of microorganisms has been developed based on automated interpretation of the results of biochemical tests or using microdilution trays following overnight incubation and photometric determination of growth (6,18,20,21). Advances in technology that may provide rapid bacterial identification and AST are now recognized as having both clinical and financial benefits (2).The VITEK system originated in the 1970s as an automated system for identification and AST and has evolved today into the VITEK 2 system, which automatically performs ...

Clinical Evaluation of QMAC-dRAST for Direct and Rapid Antimicrobial Susceptibility Test with Gram-Positive Cocci from Positive Blood Culture Bottles

“…It is noteworthy that the detection of oxacillin-resistant staphylococci with the QMAC-dRAST system was accurate even if one VME was observed in S. aureus, this result agreed with other standard AST reporting for oxacillin-resistance detection, for the agreement rates ranged from 95 to 100% [10,22]. Also, …”

“…However, these previous studies reported that direct AST methods were insufficient to handle Gram-positive bacteria, mainly applicable for Gram-negative organisms [10][11][12]. The QMAC-dRAST (Quantamatrix Inc., Seoul, Republic of Korea) system has been introduced in the clinical microbiology laboratory for expedite treatment of bloodstream infection and antibiotic-resistant strain infections via a direct inoculation of PBC [13].…”

Incidence and Antimicrobial Susceptibility of Enterococcal Infections in Tertiary Care Hospital

“…Cards were automatically filled, sealed, and loaded into the VITEK 2 instrument for incubation and reading. Card type: AST-P628 testing Instrument: 0000148FF364 (8551)card used for Enterococci contained ampicillin, ampicillin-sulbactam, cefuroxime, ciprofloxacin, clindamycin, erythromycin, high-concentration (HC) gentamicin, imipenem, HC kanamycin, levofloxacin, nitrofurantoin, norfloxacin, ofloxacin, quinupristin-dalfopristin, HC streptomycin, teicoplanin, tetracycline, trimethoprim-sulfamethoxazole, and vancomycin [13][14][15].…”

“…The results were interpreted by the ID-GPC database, and final results were obtained automatically. All cards used were automatically discarded into a waste container [13].…”

Identification of Coagulase-Negative Staphylococci by the Bruker MALDI-TOF Biotyper Compared To the Vitek 2 and MIS Gas Liquid Chromatography

“…There is a lack of reports and or studies comparing these systems ability to identify CNS with the Bruker MALDI-TOF BioTyper. Ligozzi et al [20] and Spanu et al [21] respectively reported success rates of identifying CNS with the Vitek 2 to the species level of 86% and 90,5% both these studies noted that the identification of S. hominis was problematic and needed improvement. Funke and Funke-Kissling [22] used the colorimetric based VITEK 2 ID-GP identification card and concluded that the Vitek2 was reliable in identifying staphylococci correctly [22].…”