Validation of Vitek 2 Nonfermenting Gram-Negative Cards and Vitek 2 Version 4.02 Software for Identification and Antimicrobial Susceptibility Testing of Nonfermenting Gram-Negative Rods from Patients with Cystic Fibrosis

Abstract

Accurate identification and antimicrobial susceptibility testing (AST) of nonfermenters from cystic fibrosis patients are essential for appropriate antimicrobial treatment. This study examined the ability of the newly designed Vitek 2 nonfermenting gram-negative card (NGNC) (new gram-negative identification card; bioMérieux, Marcyl'Ètoile, France) to identify nonfermenting gram-negative rods from cystic fibrosis patients in comparison to reference methods and the accuracy of the new Vitek 2 version 4.02 software for AST compared to the broth microdilution method. Two hundred twenty-four strains for identification and 138 strains for AST were investigated. The Vitek 2 NGNC identified 211 (94.1%) of the nonfermenters correctly. Among morphologically atypical microorganisms, five strains were misidentified and eight strains were determined with low discrimination, requiring additional tests which raised the correct identification rate to 97.8%. Regarding AST, the overall essential agreement of Vitek 2 was 97.6%, and the overall categorical agreement was 92.9%. Minor errors were found in 5.1% of strains, and major and very major errors were found in 1.6% and 0.3% of strains, respectively. In conclusion, the Vitek NGNC appears to be a reliable method for identification of morphologically typical nonfermenters and is an improvement over the API NE system and the Vitek 2 GNC database version 4.01. However, classification in morphologically atypical nonfermenters must be interpreted with care to avoid misidentification. Moreover, the new Vitek 2 version 4.02 software showed good results for AST and is suitable for routine clinical use. More work is needed for the reliable testing of strains whose MICs are close to the breakpoints.Pseudomonas aeruginosa is the most important cause of lung infections in patients with cystic fibrosis (CF) (14). In our hospital, 50% of sputum-producing CF patients are colonized in their lower airways with P. aeruginosa or other nonfermenting bacteria. Accurate identification and antimicrobial susceptibility testing (AST) are essential for appropriate antimicrobial therapy.A variety of automated commercial systems for identification and susceptibility testing of nonfermenting bacteria are available (2,3,12,19,20). They are widely used because of the increasing volumes of clinical specimens processed by clinical laboratories and perceived cost effectiveness. The automated systems decrease the in-laboratory turnaround time and enable a faster targeted antimicrobial therapy. Unfortunately, errors in classification and AST by any test system can have serious implications for the clinical outcome of patients. The most frequently reported errors have involved the inaccurate identification of nonfermenters due to their phenotypic variations and slower growth rates and the inconsistencies between the tested broad-spectrum ␤-lactam antibiotics. Because of the perceived inaccuracies of AST from CF isolates, a consensus conference on CF microbiology recommended the use of the disk diffusion method for ...

Comparison of Meropenem MIC by E Test and VITEK 2 in Resistant Pseudomonas and Acinetobacter Isolates

“…19 Our results are in accordance with the results of a study carried out by Providencia Joyanes et al 20 They reported very major errors for P. aeruginosa in only one strain (1.4%) of A. baumannii, for imipenem and not for meropenem. Otto Krag 21 tested 224 strains of nonfermentative Gram negatives and their conclusion supports our results that VITEK 2 is suitable for routine clinical use as the overall categorical agreement in antibiotic sensitivity testing was 92.9%. Minor errors were found in 5.1% of strains, and major and very major errors were found in 1.6% and 0.3% of strains, respectively in the same study.…”

“…Minor errors were found in 5.1% of strains, and major and very major errors were found in 1.6% and 0.3% of strains, respectively in the same study. 21 Annarita Mazzariol et al 22 demonstrated that VITEK 2 could be used with confidence for identifying resistance to several antimicrobial agents against P. aeruginosa including imipenem.…”

Phoenix 100 versus Vitek 2 in the Identification of Gram-Positive and Gram-Negative Bacteria: a Comprehensive Meta-Analysis

“…Of the 624 abstracts retrieved through the search criteria, 527 articles were excluded from the meta-analysis as irrelevant; these articles included studies assessing the VOL. 49,2011 PHOENIX 100 VERSUS VITEK 2: A META-ANALYSIS 3285 AST performance of Phoenix or Vitek 2, reports evaluating the AutoMicrobic or the first-generation Vitek system, other types of publications employing Phoenix or any of the Vitek versions for the processing of clinical isolates outside the context of an evaluation (e.g., case reports, surveillance studies, etc.) and nonmicrobiological papers.…”

<i>Alcaligenes faecalis</i>: an Unusual Cause of Skin and Soft Tissue Infection

“…In addition, all samples were cultured on Schaedler agar under anaerobic conditions. Identification of the strains was performed using the API 20 NE system (bioM áerieux, Marcy l'Etoile, France) and the Vitek II system (bioM áerieux) in accordance with reported techniques (8). The antibiotic susceptibility study was conducted using susceptibility cards manufactured by Vitek (bioM áerieux), as described previously (8).…”