Direct determination of carbapenem-resistant Enterobacteriaceae and Pseudomonas aeruginosa from positive blood cultures using laser scattering technology.

Delays in appropriate antimicrobial treatment contribute to increased mortality of septic patients. We aimed to develop a methodology for detection of carbapenem resistance in Gram-negative bacteria directly from positive blood cultures (BCs). Initially, meropenem-resistant Enterobacteriaceae (n = 13) and Pseudomonas aeruginosa (n = 32) isolates as well as the same numbers of meropenem-susceptible isolates were used to establish the detection of carbapenem resistance from agar cultures. Growth-based phenotypic detection of meropenem resistance was performed by a laser scattering (LS) method using a BacterioScan™216R instrument. A subset of the strain collection consisting of meropenem-susceptible and -resistant isolates (each comprising seven P. aeruginosa and three Klebsiella pneumoniae) was used for determination of carbapenem resistance directly from positive BCs. Lysis/centrifugation and filtration/dilution methods were investigated for processing of positive BCs. Four different statistical approaches to discriminate between susceptible and resistant bacteria in real-time were applied and were compared regarding their sensitivity and specificity. After 3 h and 4 h of incubation, respectively, detection of carbapenem resistance in Enterobacteriaceae (sensitivity, 100%; specificity, 100%) and P. aeruginosa (sensitivity, 100%; specificity, ≥90%) agar cultures was attainable. Detection of carbapenem resistance directly from positive BCs was achievable with 100% sensitivity and 100% specificity after 4 h and 5 h, respectively, applying lysis/centrifugation and filtration/dilution methods. In conclusion, LS technology combined with lysis/centrifugation and appropriate statistical real-time analyses represents a promising option for rapid detection of carbapenem resistance in Gram-negative rods directly from positive BCs.