Rapid susceptibility testing of multi-drug resistant Escherichia coli and Klebsiella by glucose metabolization monitoring

: Background The increasing number of multi-drug resistant (MDR) bacteria provides enormous challenges for choosing an appropriate antibiotic therapy in the early phase of sepsis. While bacterial identification has been greatly accelerated by the introduction of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), the antibiotic susceptibility testing (AST) remains time-consuming. Here, we present a rapid susceptibility testing method for testing Gram-negative bacteria, exemplarily validated for Escherichia coli and Klebsiella spp. Methods Gram-negative isolates (E. coli and Klebsiella spp.) were either taken as single colonies from agar plates (n=136) or directly extracted and identified from positive blood cultures (n=42) using MALDI-TOF MS. Bacteria were incubated in glucose-supplemented Luria broths (LBs) each containing one antibiotic (ceftazidime, piperacillin, imipenem and ciprofloxacin), routinely used to classify Gram-negative bacteria in Germany. To determine susceptibility the dynamics of glucose utilization in bacterial suspensions were quantitatively measured in the presence or absence of antibiotics designated liquid-AST (L-AST). Results The L-AST can be run on clinical-chemistry analyzers and integrated into laboratory routines. It yields critical resistance information within 90-150 min downstream of a MS-based identification. The results showed a high concordance with routine susceptibility testing, with less than 1% very major errors (VME) and 3.51% major errors (ME) for 178 assessed isolates. Analysis of turnaround time (TAT) for 42 clinical samples indicated that L-AST results could be obtained 34 h earlier than the routine results. Conclusions As exemplified for E. coli and Klebsiella spp., L-AST provides substantial acceleration of susceptibility testing following MALDI-TOF MS identification. The assay is a simple and low-cost method that can be integrated into clinical laboratory to allow for 24/7 AST. This approach could improve antibiotic therapy.