Comparison of two commercial systems (Vitek and MicroScan-WalkAway) for antimicrobial susceptibility testing of Pseudomonas aeruginosa isolates from cystic fibrosis patients

Diagn Microbiol Infect Dis. 2001 Apr;39(4):257-60. doi: 10.1016/s0732-8893(01)00234-6.


Antimicrobial susceptibility testing of cystic fibrosis (CF) isolates of Pseudomonas aeruginosa is difficult because the organisms are often mucoid and slow-growing. This study of 498 CF strains examined the correlation of results derived from two commonly used commercial systems (Vitek, MicroScan-WalkAway) with a reference method for 10 antimicrobials. Correlation to reference results was unacceptably low for all agents and both commercial systems had a high rate of very major (false-susceptible) errors. Although mucoid strains produced a 4.8% greater intermethod error, it was not markedly different than non-mucoid strains for the Vitek System. Overall, these tested commercial systems performed poorly for CF isolates in contrast to earlier reported, high correlations with the reference methods (broth microdilution frozen panels and agar dilution) of the National Committee for Clinical Laboratory Standards, the standardized disk diffusion test, and the Etest (AB BIODISK, Solna, Sweden).

Publication types

  • Comparative Study
  • Evaluation Study
  • Multicenter Study

MeSH terms

  • Aminoglycosides
  • Anti-Bacterial Agents / pharmacology*
  • Culture Media
  • Cystic Fibrosis / microbiology*
  • Drug Resistance, Microbial
  • Fluoroquinolones
  • Humans
  • Lactams
  • Microbial Sensitivity Tests / methods
  • Phenotype
  • Predictive Value of Tests
  • Pseudomonas aeruginosa / drug effects*
  • Pseudomonas aeruginosa / isolation & purification
  • Reagent Kits, Diagnostic / standards
  • Reference Standards


  • Aminoglycosides
  • Anti-Bacterial Agents
  • Culture Media
  • Fluoroquinolones
  • Lactams
  • Reagent Kits, Diagnostic