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Evaluation of the new WalkAway plus automated microbiology system for identification and antimicrobial susceptibility testing of Gram-negative bacilli in routine practice

Abstract number: P1866

Armand-Lefèvre L., Moreau C., Perrot M., Andremont A., Muller-Serieys C.

The WalkAway® plus (Siemens) is an automated system designed for identification (ID) and antimicrobial susceptibility testing (AST) of clinically significant human bacterial pathogens.

Objectives: We have evaluated performance of the new WalkAway® plus instrument for ID and AST of clinical Enterobacteriaceae (Eb) and non fermentative Gram-negative bacilli (Nfb) isolated in a bacteriology laboratory.

Methods: The MicroScan® Neg Fermenteur Combo Type 47 and Neg Non fermenteur Combo Type 48 panels were tested for Eb and Nfb, respectively. ID results were compared to those of conventional biochemical ID systems: API 20E (Eb) and API 20NE (Nfb) (bioMérieux, La Balme les Grottes). AST category results (S, I, R) were compared to those of the standard disk diffusion method after expertise using SIR software (I2A), and according to CA-SFM guidelines. Discrepant results were retested in duplicate. ID discrepancies were resolved by 16S rRNA sequencing. AST discordant results (I or R instead of S results and vice-versa), were resolved by MIC determination (E-test, AB biodisk).

Results: A total of 331 Eb (144 E. coli, 58 Klebsiella spp, 45 Proteus spp, 44 Enterobacter spp, 16 Citrobacter spp, 13 S. marcescens, 11 others) and 105 Nfb (84 P. aeruginosa, 8 A. baumannii, 4 S. maltophilia, 9 others), recovered from routine cultures, were tested. The percentages of concordant ID at the species levels were 97.6% (323/331) and 96.2% (101/105) for Eb and Nfb, respectively. The rate of categorical complete agreement for AST of Eb ranged from 90.6 to 99.4% for b-lactams, from 95.5 to 97.3% for aminoglycosides, 98.8% for fluoroquinolones and from 97.7 to 99.1% for other antibiotics. The lowest value (90.6%) was for the genus Proteus and aminoglycosides. Overexpression of penicillinases in E. coli caused a low concordance rate (90.6%) for the combination of amoxicillin and clavulanic acid, using the WalkAway® plus system. Among 18 ESBLs producing isolates, 4 were not detected (all were from the genus Enterobacter). Complete agreement for AST of P. aeruginosa ranged from 95.2 to 100% for b-lactams, to 95.2% for aminoglycosides and 98.8% for ciprofloxacin.

Conclusion: The new WalkAway® plus instrument is a reliable microbiology automated system for ID and AST of Enterobacteriaceae and non fermentative Gram-negative bacilli commonly isolated in a clinical laboratory.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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