Evaluation of the VITEK 2 Advanced Expert System performance for predicting resistance mechanisms in Enterobacterales acquired from a hospital-based screening program.

There is limited literature examining the accuracy of the VITEK 2 Advanced Expert System (AES) in characterisation of ß-lactamase resistance patterns. We present a prospective single centre study to better ascertain the performance characteristics of this program. The VITEK 2 AES interpretation was compared to established laboratory phenotypic methods. The overall sensitivity for detection of broad-spectrum ß-lactamase by the AES was 95%, with a specificity of 78%. One or more discrepancies were noted in 36% of samples, with the majority of these (87/100) due to incorrect 'overcall' of a resistance mechanism. AES characterisation of AmpC resistance mechanisms was excellent. In contrast, the AES had poor specificity in classifying extended spectrum ß-lactamases (ESBLs). As a screening aid, the AES can be a valuable tool. However, optimal use requires an adequate working knowledge of resistance mechanisms in order to correctly interpret and accept the result output.

Performance of the VITEK®2 advanced expert system™ for the validation of antimicrobial susceptibility testing results.

Time to reporting antimicrobial susceptibility testing (AST) results to physicians plays an essential role in antibiotic stewardship programs. Expert software has been developed for facilitating the microbiologists' AST review process. The reliability of the VITEK®2 Advanced Expert™ software to effectively alert the microbiologist in detection of atypical and inconsistent AST results was assessed at the Labor Berlin-Charité Vivantes services. The results demonstrated a confidence rate of 99.3% in reporting fully consistent AST results to physicians.

Discussion on the Problems of Vitek 2 Compact Advanced Expert System to Identify Carbapenemase Phenotypes in Isolates of Enterobacteriaceae / 现代检验医学杂志

Objective To explore the accuracy of Vitek 2 compact advanced expert system (AES) in indicating and analyze the carbapenemases-resisting Enterobacteriaceae phenotypes,and further investigate the methods to make up the AES.Methods 28 Enterobacteriaceae strains with Imipenem-Nonsusceptible by Vitek 2 compact,but AES suggested all production of carbapenemases were isolated.And imipenem susceptibility was determined by the disk diffusion method.Modified Hodge test (MHT) and the metallo-β-1actamase was detected by the double disk synergy method.Resistance genes were detected by the PCR amplification.Results ESBLs gene was amplified from all 28 selected strains,16 of which was detected KPC gene,and no strain of metallo-β-1actamases-producing bacteria.With carbapenemase gene detection as the gold standard,the accuracy of AES was 57.1％.Disc diffusion method detection accuracy rate of imipenem was 100％,and for 100％ of MHT accuracy.PCR amplification,MHT and the disk diffusion displayed the same result in detecting carbapenemases,but different with AES (x2 =10.08,P＜0.05).Conclusion The indications of the presence of carbapenemases using AES was not completely correct with a certain false-positive,and it is necessary to take other methods,such as disk diffusion or MHT methods,and improve the reliability of medicine-sensitivity tests.

Evaluation on the performance of MicroScan WalkAway in detecting carbapenem-resistant Enterobacteriaceae / 中国感染与化疗杂志

Objective To investigate the performance of MicroScan WalkAway 96 Plus (MSW) system in detection of carbapenem-resistant Enterobacteriaceae (CRE).Methods A total of 81 stock CRE strains were used in this study. Bacterial identification and antimicrobial susceptibility test were performed by MSW system. Beta-lactamases genes blaKPC,blaIMP,blaVIM, blaOXA-48 and blaNDM were amplified by PCR and subjected to sequencing analysis. Disk diffusion method and PCR were used as gold standard to evaluate the performance and reliability of MSW system in identifying carbapenem-resistant and carbapenemase-producing Enterobacteriaceae.Results Overall, 69.1 % (56/81) of the Enterobacteriaceae strains were identified as CRE by the MSW system. The results of PCR showed that 48 strains were carbapenemase-producing Enterobacteriaceae. When carbapenemase-producing Enterobacteriaceae strains were identified by the instrument using an advanced expert system, the sensitivity was 93.8 % and specificity was 42.4 %. The positive predictive value was 70.3 %, the negative predictive value was 82.4 % and the predictive accuracy value was 72.8 %.Conclusions The MicroScan WalkAway 96 Plus system has shown good performance in detection of CRE.

Performance and reliability of VITEK 2-Compact GN13 method and its Advanced Expert System validation for testing imipenem susceptibility of Klebsiella pneumoniae / 中国感染与化疗杂志

Objective To evaluate the performance of VITEK 2-Compact GN13 methods for testing imipenem susceptibility of Klebsiella pneumoniae and assess the reliability of its Advanced Expert System (AES).Methods A retrospective study was conducted with a total of 157K. pneumoniae strains, which were isolated from blood and intra-abdominal infections in the First Affiliated Hospital of Nanchang University from 2014 to 2015. Thein vitro minimum inhibitory concentration (MIC) values of imipenem were determined by disc diffusion, VITEK 2-Compact GN13 and broth microdilution methods, respectively. Categorical agreement (CA) rates of disc diffusion and VITEK 2-Compact GN13 methods were determined using broth microdilution as reference method. The genes encoding ESBLs and carbapenemase were screened by PCR and sequencing analysis. The phenotypic confirmatory tests such as modified Hodge test, PCR and DNA sequencing were used to confirm the resistance mechanism and evaluate the reliability of AES in interpreting the imipenem susceptibility of K. pneumoniae.Results Among the 157 isolates, 64 and 8 were identified as resistant and intermediate strains by broth microdilution method, respectively; 52 and 10 were tested as resistant and intermediate strains by disc diffusion method, respectively; 54 and 13 were determined as resistant and intermediate strains by VITEK 2-Compact GN13 method, respectively, while 70 and 3 were judged as resistant and intermediate strains by VITEK 2-Compact GN13 method plus AES validation. The CA of disc diffusion and VITEK 2-Compact GN13 methods compared with broth microdilution method were all higher than 90 %. However, the major error (ME) rate was 3.8 % and very major error (VME) rates were all 0.6 % in imipenem susceptibility testing by VITEK 2-Compact GN13 and disc diffusion. The imipenem susceptibility of 16 strains were modified by the AES, which eliminated 0.6 % VME, but increased major error by 1.3 % and minor error by 1.9 %. Phenotypic confirmatory tests showed that 75 % (12/16) of these strains were validated as producers of both ESBLs and carbapenemase, which was consistent with the result of AES validation. PCR and DNA sequencing analysis proved that 62.5 % (10/16) of these strains produce IMP-4/KPC-2 /NDM-1 and ESBLs.Conclusions Both disc diffusion and VITEK 2-Compact GN13 methods can be used for testing the imipenem susceptibility of K. pneumoniae isolates with reliable and accurate results. Attention should be paid to the possibility of ME and VME when testing imipenem susceptibility. The VME can be avoided by the AES mechanism. However, AES intervention will increase ME and minor error, which may be associated with decreased expression of carbapenemase.