Evaluation of VITEK 2 rapid identification and susceptibility testing system against gram-negative clinical isolates

A total of 281 strains of miscellaneous members of the family Enterobacteriaceae, Pseudomonas aeruginosa, and other gram-negative bacteria were evaluated by use of identification tests with the VITEK 2 system (bioMérieux) and an API identification system (bioMérieux). A total of 237 (95%) strains were correctly identified to the species level. Only six (2.1%) strains were misidentified, and eight (2.8%) strains were not identified. Among 14 strains with discrepant identifications, 8 (57.1%) strains were nonfermenters. The susceptibilities of 228 strains to 11 antibiotics including amikacin, netilmicin, tobramycin, gentamicin, ciprofloxacin, imipenem, meropenem, ceftazidime, cefepime, piperacillin, and piperacillin in combination with tazobactam were tested with the VITEK 2 AST-No. 12 card and by the broth microdilution (MB) method, according to NCCLS guidelines, as a reference. For the 2,508 organism-antibiotic combinations, the rates at which duplicate MICs correlated within +/-1 dilution ranged from 84.2 to 95.6%. Only 13 (0.5%) and 10 (0.4%) of the susceptibility tests gave major errors (resistant with the VITEK 2 system but sensitive by the MB method) and very major errors (sensitive with the VITEK 2 system but resistant by the MB method), respectively. Both VITEK 2 ID-GNB (an identification system) and VITEK 2 AST-No. 12 (a susceptibility testing system) card systems gave rapid, reliable, and highly reproducible results.     

Evaluation of the VITEK 2 system for rapid identification of yeasts and yeast-like organisms

The new VITEK 2 system is a fully automated system dedicated to the identification and susceptibility testing of microorganisms. In conjunction with the VITEK ID-YST card the VITEK 2 system allows the identification of clinically important yeasts and yeast-like organisms in 15 h due to a sensitive fluorescence-based technology. The ID-YST card consists of 47 biochemical reactions. The database comprises 51 taxa, including newly described species. In this study we evaluated the reliability of the VITEK ID-YST card for the identification of yeasts and yeast-like organisms encountered in a clinical microbiology laboratory. A total of 241 strains representing 21 species were studied. The strains were isolated from clinical samples within a period of 60 days prior to the identification. The tests were performed using 24-h to 55-h subcultures on Sabouraud-gentamicin-chloramphenicol agar. Each strain was tested in parallel using the ID 32C strip as a comparison method combined with microscopic morphology and an agglutination test for C. krusei. Overall, 222 strains (92.1%) were unequivocally identified including 11 isolates (4.6%) identified with low discrimination resolved by simple additional tests. Ten strains (4. 1%) for which results were given with low discrimination could not be unequivocally identified with supplemental tests, 4 strains (1. 7%) were misidentified and 5 strains (2.1%) could not be identified. In conclusion, we found that the VITEK 2 system is a rapid and accurate method for the identification of medically important yeasts and yeast-like organisms.     

Accuracy of the VITEK 2 system to detect glycopeptide resistance in enterococci

We evaluated the accuracy of the VITEK 2 fully automated system to detect and identify glycopeptide-resistant enterococci (GRE) compared to a reference agar dilution method. The sensitivity of vancomycin susceptibility testing with VITEK 2 for the detection of vanA, vanB, and vanC1 strains was 100%. The sensitivity of vancomycin susceptibility testing of vanC2 strains was 77%. The sensitivity of teicoplanin susceptibility testing of vanA strains was 90%. Of 80 vanC enterococci, 78 (98%) were correctly identified by VITEK 2 as Enterococcus gallinarum/Enterococcus casseliflavus. Since the identification and susceptibility data are produced within 3 and 8 h, respectively, VITEK 2 appears a fast and reliable method for detection of GRE in microbiology laboratories.     

Microbiological evaluation of the new VITEK 2 Neisseria-Haemophilus identification card

VITEK 2 is an automated identification system for diverse bacterial and fungal species. A new card (the Neisseria-Haemophilus [NH] card) for the identification of Neisseria spp., Haemophilus spp., and other fastidious gram-negative or gram-variable microorganisms has been developed, but its performance in a routine clinical laboratory has not yet been evaluated. In this study, a total of 188 bacterial strains belonging to the genera Actinobacillus, Campylobacter, Capnocytophaga, Cardiobacterium, Eikenella, Gardnerella, Haemophilus, Kingella, Moraxella, and Neisseria were investigated. The NH card was able to identify 171 strains (91%) correctly without the need for extra tests; one strain (0.5%) was misidentified, and five strains (2.7%) could not be classified. Eleven strains (5.8%) were identified with a low level of discrimination, and simple additional tests were required to increase the correct-identification rate to 96.8%. The results were available within 6 h. Based on these results, the new VITEK 2 NH card appears to be a good method for the identification of diverse groups of fastidious organisms, which would otherwise require testing with multiple systems. However, more work is needed to evaluate the performance of VITEK 2 with regard to Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, and Kingella bacteria because of the insufficient number of strains tested in this study. Moreover, further reduction of the detection time would be desirable.     

Evaluation of the VITEK 2 system for identification and antimicrobial susceptibility testing of medically relevant gram-positive cocci

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.     

Multicenter evaluation of the new VITEK 2 advanced colorimetric yeast identification card

The performance of the new VITEK 2 Advanced Colorimetry yeast identification (YST) card for use with the VITEK 2 system (bioMérieux, Inc., Hazelwood, MO) was compared to that of the API 20C AUX (API) system (bioMérieux SA, Marcy-l'Etoile, France) in a multicenter evaluation. A total of 12 quality control, 64 challenge, and 623 clinical yeast isolates were used in the study. Comparisons of species identification, platform reliability, and substrate reproducibility were made between YST and API, with API considered the reference standard. Quality control testing to assess system and substrate reproducibility matched expected results >/=95% of the time. The YST card correctly identified 100% of the challenge strains, which covered the species range of the manufacturer's performance claims. Using clinical isolates, the YST card correctly identified 98.5%, with 1.0% of isolates incorrectly identified and 0.5% unidentified. Among clinical isolates, the YST card generated fewer low-discrimination results (18.9%) than did API (30.0%). The time to identification with YST was 18 h, compared to 48 to 72 h with API. The colorimetric YST card used with the VITEK 2 provides a highly automated, objective yeast identification method with excellent performance and reproducibility. We found this system useful for timely and accurate identification of significant yeast species in the clinical microbiology laboratory.     

Evaluation of the colorimetric VITEK 2 card for identification of gram-negative nonfermentative rods: comparison to 16S rRNA gene sequencing

Ninety strains of a collection of well-identified clinical isolates of gram-negative nonfermentative rods collected over a period of 5 years were evaluated using the new colorimetric VITEK 2 card. The VITEK 2 colorimetric system identified 53 (59%) of the isolates to the species level and 9 (10%) to the genus level; 28 (31%) isolates were misidentified. An algorithm combining the colorimetric VITEK 2 card and 16S rRNA gene sequencing for adequate identification of gram-negative nonfermentative rods was developed. According to this algorithm, any identification by the colorimetric VITEK 2 card other than Achromobacter xylosoxidans, Acinetobacter sp., Burkholderia cepacia complex, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia should be subjected to 16S rRNA gene sequencing when accurate identification of nonfermentative rods is of concern.     

Accuracy and reproducibility of the AutoMicrobic System Gram-Negative General Susceptibility-Plus Card for testing selected challenge organisms.

A total of 180 selected strains of gram-negative bacilli were tested for susceptibility to nine antibiotics by the prototype General Susceptibility Card and reference broth microdilution MIC method, and 112 of 180 were tested by the modified Gram-Negative General Susceptibility-Plus Card (Vitek Systems, Inc., Hazelwood, Mo.). When category calls--susceptible, intermediate, and resistant for the prototype card and very susceptible, moderately susceptible, and resistant for the modified card--were identical or compatible (very susceptible by one method and moderately susceptible by the other), the methods were considered in qualitative or categorical agreement. The overall categorical agreement improved from 83% for the prototype card to 91.5% for the modified card, and the frequency of major and very major disagreements was reduced from 7.5 to 1%, respectively. Overall agreement between the modified card and reference method for both category calls and MICs (+/- 2 dilutions) was 90%. Of the results, 67% were identical, 22% were more susceptible with the modified card, and 11% were more resistant. Reproducibility of identical or compatible category calls and MICs obtained from three trials was 94.5%. The poorest accuracy and reproducibility were observed when testing Pseudomonas aeruginosa. The study suggests that the modified card can rapidly and efficiently perform susceptibility tests with an acceptable level of accuracy and reproducibility provided that the system is appropriately used for testing strains of the family Enterobacteriaceae with preset criteria for excluding organism-antibiotic combinations. The evaluation also indicates dramatic improvement in the technical performance of the modified card compared with its earlier prototype.     

醋酸钙-鲍曼不动杆菌复合体的精确鉴定与药敏分析

目的精确鉴定醋酸钙-鲍曼不动杆菌复合体菌株;检测菌株对氨基糖苷类抗生素和碳青霉烯类抗生素的敏感性。方法运用自动化分析仪VITEK 2试卡法对临床分离不动杆菌进行菌种鉴定,对鉴定为醋酸钙-鲍曼不动杆菌复合体的菌株进一步经16S rRNA序列分析确证其准确种属。分别用自动化分析仪VITEK 2和微稀释法测定精确鉴定后的醋酸钙-鲍曼不动杆菌复合体菌株对阿米卡星、庆大霉素、妥布霉素、亚胺培南和厄他培南五种抗生素的敏感性,分析药敏实验结果。结果共进行了232株不动杆菌的VITEK 2鉴定,其中195株鉴定为醋酸钙-鲍曼不动杆菌复合体。对195株醋酸钙-鲍曼不动杆菌复合体菌株进一步用16S rRNA序列分析确证其准确种属,结果显示173株为鲍曼不动杆菌,22株为醋酸钙不动杆菌。对173株鲍曼不动杆菌及22株醋酸钙不动杆菌分别用VITEK 2和微稀释法进行阿米卡星、庆大霉素、妥布霉素、亚胺培南和厄他培南五种抗生素的药敏检测。微稀释法药敏结果显示,受试鲍曼不动杆菌对三种氨基糖苷类抗生素均呈现高水平耐药,而对两种碳青霉烯类抗生素敏感度较高;受试醋酸钙不动杆菌对五种抗生素均呈现较高敏感度。与微稀释法药敏检测结果相比,VITEK 2试卡法药敏结果中受试鲍曼不动杆菌和醋酸钙不动杆菌对各抗生素的药敏检测结果均出现了不同程度的误差,鲍曼不动杆菌药敏检测结果中阿米卡星符合率最低,严重错误率高达34.10%;醋酸钙不动杆菌药敏检测结果中厄他培南符合率最低,重大错误率高达40.91%。结论 VITEK 2在不动杆菌种属鉴定中存在局限性,辅以16S rRNA序列分析,方可精确鉴定醋酸钙-鲍曼不动杆菌复合体。鲍曼不动杆菌对氨基糖苷类抗生素耐药现状严重。用VITEK 2进行鲍曼不动杆菌和醋酸钙不动杆菌对氨基糖苷类和碳青霉烯类的药敏测定时存在不同程度的误差,建议辅以微稀释法。     

Evaluation of a new system, VITEK 2, for identification and antimicrobial susceptibility testing of enterococci

We evaluated the new automated VITEK 2 system (bioMérieux) for the identification and antimicrobial susceptibility testing of enterococci. The results obtained with the VITEK 2 system were compared to those obtained by reference methods: standard identification by the scheme of Facklam and Sahm [R. R. Facklam and D. F. Sahm, p. 308-314, in P. R. Murray et al., ed., Manual of Clinical Microbiology, 6th ed., 1995] and with the API 20 STREP system and, for antimicrobial susceptibility testing, broth microdilution and agar dilution methods by the procedures of the National Committee for Clinical Laboratory Standards. The presence of vanA and vanB genes was determined by PCR. A total of 150 clinical isolates were studied, corresponding to 60 Enterococcus faecalis, 55 Enterococcus faecium, 26 Enterococcus gallinarum, 5 Enterococcus avium, 2 Enterococcus durans, and 2 Enterococcus raffinosus isolates. Among those isolates, 131 (87%) were correctly identified to the species level with the VITEK 2 system. Approximately half of the misidentifications were for E. faecium with low-level resistance to vancomycin, identified as E. gallinarum or E. casseliflavus; however, a motility test solved the discrepancies and increased the agreement to 94%. Among the strains studied, 66% were vancomycin resistant (57 VanA, 16 VanB, and 26 VanC strains), 23% were ampicillin resistant (MICs, >/=16 microgram/ml), 31% were high-level gentamicin resistant, and 45% were high-level streptomycin resistant. Percentages of agreement for susceptibility and resistance to ampicillin, vancomycin, and teicoplanin and for high-level gentamicin resistance and high-level streptomycin resistance were 93, 95, 97, 97, and 96%, respectively. The accuracy of identification and antimicrobial susceptibility testing of enterococci with the VITEK 2 system, together with the significant reduction in handling time, will have a positive impact on the work flow of the clinical microbiology laboratory.     

Comparative evaluation of Vitek 2 identification and susceptibility testing of Gram-negative rods directly and isolated from BacT/ALERT-positive blood culture bottles

The performance of Vitek 2 was evaluated for the identification and susceptibility testing of Gram-negative bacilli directly from positive blood cultures bottles. Direct inoculation of the positive blood cultures with the Vitek cards ID-GN and AST-NO58 was compared with the standard inoculation method based on the sub-culture of the positive blood culture to agar. A total of 142 blood cultures were included in the study; of those, 119 were from patients’ clinical samples, while 23 were artificially prepared with strains showing different mechanisms of resistance. A total of 136 (95.8%) strains were correctly identified to the species level, only 2 (1.4%) were mis-identified and 4 (2.8%) were not identified. Susceptibility results were available for all isolates tested against 17 antibiotics, thus, resulting in a total of 2,414 isolate/anti-microbial combinations. The error rate was 2.8% (67/2,414) overall; 0.6% (14/2,414) very major errors, 0.1% (3/2,414) major errors and 2.1% (50/2,414) minor errors. The direct method detected 88.5% (22/25) of the strains producing extended-spectrum beta-lactamases (ESBLs). The susceptibility agreement among the added strains with ESBL, AMPc hyperproduction, resistance to ceftazidime, carbapenems and cefepime was very high. Direct identification and susceptibility testing gave rapid and reliable results, reducing by 24 h the turnaround time of the microbiology laboratory.     

Analysis of the comparative workflow and performance characteristics of the VITEK 2 and Phoenix systems

The VITEK 2 (bioMérieux, Marcy L'Etoile, France) and the Phoenix systems (BD Diagnostic Systems, Sparks, Md.) are automated instruments for rapid organism identification and susceptibility testing. We evaluated the workflow, the time to result, and the performance of identification and susceptibility testing of both instruments. A total of 307 fresh clinical isolates were tested: 141 Enterobacteriaceae, 22 nonfermenters, 93 Staphylococcus spp., and 51 Enterococcus spp. Manipulation time was measured in batches, each with seven isolates, for a total of 39 batches. The mean (+/- standard deviation [SD]) manipulation time per batch was 20.9 +/- 1.8 min for Phoenix and 10.6 +/- 1.0 min for VITEK 2 (P < 0.001). Mean (+/-SD) time to result for all bacterial groups was 727 +/- 162 min for Phoenix and 506 +/- 120 min for VITEK 2 (P < 0.001). Concerning identification, Phoenix and VITEK 2 yielded the same results for nonfermenters (100%), staphylococci (97%), and enterococci (100%). For 140 Enterobacteriaceae strains evaluated, 135 (96%) were correctly identified by Phoenix and 137 (98%) by VITEK 2 (P = 0.72). The overall category agreement for all isolates was 97.0% for both instruments. The minor error rate, major error rate, and very major error rate for all bacterial isolates tested were 3.0, 0.3, and 0.6 and 2.8, 0.2, and 1.7 for Phoenix and VITEK 2, respectively (P values of 0.76, 0.75, and 0.09). The VITEK 2 system required less manual manipulation time and less time than the Phoenix system to yield results.     

Performance of the new VITEK 2 GP card for identification of medically relevant gram-positive cocci in a routine clinical laboratory

The VITEK 2 gram-positive (GP) identification card (bioMerieux, Marcy l'Etoile, France) has been redesigned to achieve greater accuracy in the identification of gram-positive cocci. A total of 43 biochemical tests, including 17 enzymatic tests, are present in the card and interpreted in a kinetic mode, for up to 8 h. The VITEK 2 database, used in conjunction with the GP identification card, allows the identification of 115 different taxa. A total of 364 strains of GP cocci (217 Streptococcaceae strains and 147 Micrococcaceae strains) belonging to 31 taxa were tested with the new VITEK 2 GP identification card. Of the 364 strains, 105 were taken from routine primary plating media. A total of 344 strains (94.5%) were correctly identified to the species level and 17 strains (4.7%) were identified with low discrimination, requiring additional tests, whereas 1 strain (0.3%) was incorrectly identified and 2 strains (0.5%) remained unidentified. Within 7 h of the start of incubation, more than 90% of all strains were identified. Of the 105 primary cultures, 97% were correctly identified to the species level, 2% were identified with low discrimination, and 1% remained unidentified. Identification performance data were independent of each of the three plating media used. It is concluded that the new VITEK 2 GP identification card provides reliable results for the identification of GP cocci under routine laboratory conditions.     

Potential Impact of the VITEK 2 System and the Advanced Expert System on the Clinical Laboratory of a University-Based Hospital

A study was designed to assess the impact of the VITEK 2 automated system and the Advanced Expert System (AES) on the clinical laboratory of a typical university-based hospital. A total of 259 consecutive, nonduplicate isolates of Enterobacteriaceae members, Pseudomonas aeruginosa, and Staphylococcus aureus were collected and tested by the VITEK 2 system for identification and antimicrobial susceptibility testing, and the results were analyzed by the AES. The results were also analyzed by a human expert and compared to the AES analyses. Among the 259 isolates included in this study, 245 (94.6%) were definitively identified by VITEK 2, requiring little input from laboratory staff. For 194 (74.9%) isolates, no inconsistencies between the identification of the strain and the antimicrobial susceptibility determined by VITEK 2 were detected by the AES. Thus, no input from laboratory staff was required for these strains. The AES suggested one or more corrections to results obtained with 65 strains to remove inconsistencies. The human expert thought that most of these corrections were appropriate and that some resulted from a failure of the VITEK 2 system to detect certain forms of resistance. Antimicrobial phenotypes assigned to the strains by the AES for beta-lactams, aminoglycosides, quinolones, macrolides, tetracyclines, and glycopeptides were similar to those assigned by the human expert for 95.7 to 100% of strains. These results indicate that the VITEK 2 system and AES can provide accurate information in tests for most of the clinical isolates examined and remove the need for human analysis of results for many. Certain problems were identified in the study that should be remediable with further work on the software supporting the AES.     

Evaluation of the new VITEK 2 card for identification of clinically relevant gram-negative rods

The VITEK 2 card for gram-negative bacteria (bioMérieux,Marcy-l'Etoile, France) has been redesigned to improve the identification of fermenting and nonfermenting bacilli. Forty-seven biochemical tests, including 19 enzymatic tests, are present in the new card and interpreted in a kinetic mode. Final identification results are available within 10 h. The database allows the identification of 159 different taxa. Six hundred fifty-five gram-negative rods (GNR; 511 fermenters and 144 nonfermenters), representing 54 taxa, were tested. Strains were taken from fresh routine primary isolation plates (n = 157), from stored routine plates (n = 301), and from stock cultures (n = 197). Six hundred thirty-seven strains (97.3%) were correctly identified to the species level, 14 strains (2.1%) gave low discrimination results requiring additional tests, and 4 strains (0.6%) gave discordant results; not a single strain remained unidentified. Nearly 92% of all isolates were correctly identified within 7 h of incubation. The robustness of the system was demonstrated by the fact that strains were grown on four different agar media before testing. The system may also have the potential to be applied directly to primary isolation plates, since in this instance 96.2% of 157 GNR were correctly identified and 3.8% gave low discrimination results. The new VITEK 2 card for gram-negative bacteria seems to be a promising new tool for routine, rapid identification of GNR.     

Evaluation of the VITEK 2 AST-N111 card for detection of extended-spectrum beta-lactamases (ESBLs) in <Emphasis Type="Italic">Escherichia coli,Klebsiella pneumoniae,</Emphasis> and <Emphasis Type="Italic">Klebsiella oxytoca</Emphasis> compared to ESBL Etests and combination disk methods

The VITEK 2 AST-N111 card was evaluated for detection of extended-spectrum beta-lactamases (ESBLs) by testing 51 ESBL positive and 50 ESBL negative isolates of E. coli, K. pneumoniae, and K. oxytoca. The occurrence of beta-lactamase genes was confirmed by PCR and sequencing. The advanced expert system (AES) of the VITEK 2 system achieved sensitivity and specificity values of 100% and 96.0%, respectively. The ESBL test of the VITEK 2 AST-N111 card showed a sensitivity of 92.1% and a specificity of 90.0%. Contradictory results obtained with the two VITEK 2 tools could be clarified by combination disk tests in nine of 11 isolates. The combined use of AES and ESBL tests of the AST-N111 card in association with combination disk tests in case of contradictory results seems to be a reliable method for ESBL detection.     

Multicenter comparison of the VITEK 2 yeast susceptibility test with the CLSI broth microdilution reference method for testing fluconazole against Candida spp

A fully automated commercial antifungal susceptibility test system (VITEK 2 yeast susceptibility test; bioMerieux, Inc., Hazelwood, Mo.) was compared in three different laboratories with Clinical and Laboratory Standards Institute (CLSI) reference broth microdilution (BMD) method by testing two quality control strains and a total of 426 isolates of Candida spp. (103 to 135 clinical isolates in each laboratory plus 80 challenge isolates in one laboratory) against fluconazole. Reference BMD MIC endpoints were established after 24 and 48 h of incubation. VITEK 2 endpoints were determined spectrophotometrically after 10 to 26 h of incubation (mean, 13 h). Excellent essential agreement (within two dilutions) between the VITEK 2 and the 24- and 48-h BMD MICs was observed. The overall agreement values were 97.9 and 93.7%, respectively. Both intra- and interlaboratory agreement was 100%. The overall categorical agreement between VITEK 2 and BMD was 97.2% at the 24-h BMD time point and 88.3% at the 48-h BMD time point. Decreased categorical agreement at 48 h was attributed to trailing growth observed with Candida glabrata. The VITEK 2 system reliably detected fluconazole resistance among Candida spp. and demonstrated excellent quantitative and qualitative agreement with the reference BMD method.     

Validation of VITEK 2 version 4.01 software for detection, identification, and classification of glycopeptide-resistant enterococci

We evaluated the ability of the new VITEK 2 version 4.01 software to identify and detect glycopeptide-resistant enterococci compared to that of the reference broth microdilution method and to classify them into the vanA, vanB, vanC1, and vanC2 genotypes. Moreover, the accuracy of antimicrobial susceptibility testing with agents with improved potencies against glycopeptide-resistant enterococci was determined. A total of 121 enterococci were investigated. The new VITEK 2 software was able to identify 114 (94.2%) enterococcal strains correctly to the species level and to classify 119 (98.3%) enterococci correctly to the glycopeptide resistance genotype level. One Enterococcus casseliflavus strain and six Enterococcus faecium vanA strains with low-level resistance to vancomycin were identified with low discrimination, requiring additional tests. One of the vanA strains was misclassified as the vanB type, and one glycopeptide-susceptible E. facium wild type was misclassified as the vanA type. The overall essential agreements for antimicrobial susceptibility testing results were 94.2% for vancomycin, 95.9% for teicoplanin, 100% for quinupristin-dalfopristin and moxifloxacin, and 97.5% for linezolid. The rates of minor errors were 9% for teicoplanin and 5% for the other antibiotic agents. The identification and susceptibility data were produced within 4 h to 6 h 30 min and 8 h 15 min to 12 h 15 min. In conclusion, use of VITEK 2 version 4.01 software appears to be a reliable method for the identification and detection of glycopeptide-resistant enterococci as well as an improvement over the use of the former VITEK 2 database. However, a significant reduction in the detection time would be desirable.     

Multicenter comparison of the VITEK 2 antifungal susceptibility test with the CLSI broth microdilution reference method for testing amphotericin B, flucytosine, and voriconazole against Candida spp

A fully automated commercial antifungal susceptibility test system (VITEK 2; bioMérieux, Inc., Hazelwood, MO) was compared in three different laboratories with the Clinical and Laboratory Standards Institute (formerly the NCCLS) reference broth microdilution method (BMD) by testing 2 quality control strains, 10 reproducibility strains, and 426 isolates of Candida spp. against amphotericin B, flucytosine, and voriconazole. Reference BMD MIC endpoints were established after 24 and 48 h of incubation. VITEK 2 system MIC endpoints were determined spectrophotometrically after 9.1 to 27.1 h of incubation (mean, 12 to 14 h). Excellent essential agreement (within 2 dilutions) between the VITEK 2 system and the 24- and 48-h BMD MICs was observed for all three antifungal agents: amphotericin B, 99.1% and 97%, respectively; flucytosine, 99.1% and 98.8%, respectively; and voriconazole, 96.7% and 96%, respectively. Both intra- and interlaboratory agreements were >98% for all three drugs. The overall categorical agreements between the VITEK 2 system and BMD for flucytosine and voriconazole were 98.1 to 98.6% at the 24-h BMD time point and 96.9 to 97.4% at the 48-h BMD time point. The VITEK 2 system reliably detected flucytosine and voriconazole resistance among Candida spp. and demonstrated excellent quantitative and qualitative agreement with the reference BMD method.     

Evaluation of VITEK 2 for analysis of Enterobacteriaceae using the Advanced Expert System (AES) versus interpretive susceptibility guidelines used at Dynacare Kasper Medical Laboratories, Edmonton, Alberta

Objective  To evaluate the applicability and adaptability of the bioMérieux VITEK 2 Advanced Expert System (AES) to the customized interpretive susceptibility guidelines used at Dynacare Kasper Medical Laboratories (DKML).
Methods  Three hundred isolates of Enterobacteriaceae (not more than 30% Escherichia coli ) were tested on the VITEK 2 system and the API 20E for identification. Susceptibility testing for these isolates was performed on the VITEK 2 system and the Pasco broth microdilution panels. Minimal inhibitory concentrations (MICs) and interpreted results according to the AES and DKML antimicrobial susceptibility guidelines were compared.
Results  Of 300 isolates tested for susceptibility, 13 did not give AES interpretations. Of the remaining 287 isolates, interpretations between AES and DKML guidelines were compared for 10 antibiotics. The overall correlation between the AES and DKML interpretations was 96.2%.
Conclusion  This study demonstrated the benefits and limitations of the bioMérieux AES. Automated knowledge-based systems provide a useful laboratory tool for the interpretation of susceptibility results.