Detection of carbapenemase activity using VITEK MS: interplay of carbapenemase type and period of incubation

Recently, the carbapenemase activity of Gram-negative bacilli has been detected by matrix-assisted laser desorption ionizationtime of flight (MALDI-TOF) MS (Burckhardt & Zimmermann, 2011; Carvalhaes et al., 2013). This method relies on the modification of the mass spectrum profile of the carbapenem molecule by carbapenemases (Burckhardt & Zimmermann, 2011). Most studies have evaluated ertapenem hydrolysis by testing the Microflex LT instrument (Bruker Daltonics) (Carvalhaes et al., 2013). To the best of our knowledge, only one recently published study evaluated the detection of carbapenemase activity by using the VITEK MS instrument (bioMérieux) (Knox et al., 2014). The authors reported a lack of sensitivity (87 %) by testing imipenem as substrate. Recently, we assessed the performance of VITEK MS for detection of carbapenemase activity by testing a wellcharacterized collection of carbapenemaseproducing strains against ertapenem activity. In addition, as carbapenem hydrolysis may depend on many factors, especially carbapenemase type and time required for complete b-lactam hydrolysis (Carvalhaes et al., 2013), the interplay amongst different classes of carbapenemases and period of incubation required for carbapenemase detection by VITEK MS were also addressed in the present study.