Vitek MICs as first-line phenotypic screening method for carbapenemase-producing Pseudomonas aeruginosa

To define sensitivity and specificity of Vitek® 2 MICs as phenotypic screening method for carbapenemase-producing Pseudomonas aeruginosa. Materials & methods: We determined Vitek® 2 MICs of antipseudomonal antimicrobials in 130 unrelated carbapenemase-producing P. aeruginosa and 129 carbapenemase-negative P. aeruginosa isolates within a Dutch carbapenemase-surveillance database. We calculated test characteristics of single and combined antimicrobial MICs for carbapenemase production. Results: Vitek® 2 MIC above epidemiological cutoff of both imipenem and tobramycin or ciprofloxacin and tobramycin displayed a sensitivity of 96.2% and specificity of 89.6% for carbapenemase production in P. aeruginosa. Conclusion: Vitek® 2 MIC> epidemiological cut-off values seem sensitive and specific as a phenotypic screening strategy for carbapenemase-producing P. aeruginosa. Combining imipenem and tobramycin or ciprofloxacin and tobramycin performed best as a screening strategy for defining which P. aeruginosa isolates should undergo confirmatory tests for carbapenemase production.