Impact of rapid pathogen identification of gram-negative anaerobic bacteria from blood cultures on antimicrobial stewardship

Anaerobic bacteria are an important but understudied cause of bacteremia. The objective of this study was to evaluate the impact of using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to rapidly identify obligate anaerobic gram-negative bacteria directly from positive blood culture broth (PBCB) samples. This retrospective pre- and post-intervention study included patients with blood cultures positive for anaerobic gram-negative organisms, comparing outcomes before and after the implementation of a direct-from-PBCB MALDI-TOF MS workflow. The primary outcome was the time from Gram stain to organism identification. A secondary outcome was the time to first antibiotic modification (escalation or de-escalation). In monomicrobial anaerobic bloodstream infections, the median (interquartile range [IQR]) time from Gram stain to pathogen identification was significantly reduced in the post-intervention group compared to the pre-intervention group (15.0 hours [IQR: 7.8-47.8] vs 45.3 hours [IQR: 41.5-49.3]; <i>P</i> < 0.001). Similarly, the median (IQR) time to the first antibiotic de-escalation was significantly shorter following implementation of directly-from-PBCB MALDI-TOF MS (21.1 hours [IQR: 7.9-51.6] vs 52.0 hours [IQR: 24.0-64.5]; <i>P</i> = 0.014). This study demonstrates that the rapid identification of gram-negative obligate anaerobes from PBCB can help to significantly expedite antibiotic therapy de-escalation.IMPORTANCEObligate anaerobic gram-negative organisms are a significant but understudied cause of bloodstream infections. This study demonstrates that rapid identification of anaerobic gram-negative bacteria directly-from-positive blood culture broth by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry can substantially reduce the time to both pathogen identification and antibiotic optimization in monomicrobial bloodstream infections. Faster diagnostic turnaround supports more timely and targeted therapy, with important implications for antimicrobial stewardship and patient outcomes.