Rapid identification and detection of β-lactamase-producing Enterobacteriaceae from positive blood cultures by...

Current evidence suggests that early diagnosis of sepsis and timely detection of antimicrobial resistance are crucial to improve mortality rates among patients. The aim of this study was to evaluate a rapid method for the identification of Gram-negative bacteria from positive blood cultures (BCs), combined with the detection of extended spectrum β-lactamases (ESβL) and carbapenemases production, by means of MALDI-TOF/MS analysis.

During the study, all BCs positive for Gram-negative rods were selected. Starting from bacterial pellets obtained directly from BC broths, species identification and hydrolysis assays were achieved through MALDI-TOF/MS (Bruker). In particular, we performed a hydrolysis assays of cefotaxime (CTX) and ertapenem (ERT) for the rapid detection of resistance via ESβL and carbapenemases, respectively. These results were compared with the routine workflow, including BC subcultures and confirmation phenotypic methods. Finally, a comparison of the turnaround-time (TAT) between the two protocols was conducted.

Overall, 185 BCs positive for Enterobacteriaceae were collected. In terms of species identification, we observed a concordance of 95.9% comparing MALDI-TOF/MS results to the subculture-based method. The sensitivity and specificity for CTX hydrolysis assay were 91.1% and 92%, respectively; ERT hydrolysis assay showed a sensitivity of 96.2% and a specificity of 99.2%. The TAT of the proposed MALDI TOF/MS-based protocol was significantly lower compared with the routine workflow (P <  0.0001).

The proposed protocol can provide reliable bacterial identification and data concerning β-lactam resistance in only 3 hours, positively improving management of patients in terms of antimicrobial stewardship.