1651. In vitro synergy test and clinical outcome of antibiotics combination regimens for carbapenem-resistant Acinetobacter baumannii
Abstract
Acinetobacter baumannii is one of the leading etiologic agents of serious hospital-acquired infections. A. baumannii is characterized by a high rate of carbapenem resistance, which often leads to treatment failure and poor outcome. Combination regimens of antibiotics are often used, but their clinical benefit and optimal target are yet unclear.
We selected carbapenem-resistant A. baumannii (CRA) isolates from the patients who received antimicrobial treatment for bloodstream infection (2012–2018) or pneumonia (2019–2020) and survived for ≥5 days. In vitro synergy was tested using checkerboard method and time-kill assay for colistin (COL) and tigecycline (TGC) with the following antibiotics: meropenem (MRO), ampicillin/sulbactam (A/S), minocycline (MIN), ciprofloxacin (CIP), and with each other. Clinical information was collected to compare the patient outcome between those who were treated with combination regimens with in vitro synergy and those who were not.
A total of 72 isolates were selected. When combined with colistin, MRO showed the highest rate of synergy (20.8%), followed by A/S (16.7%), and MIN (13.9%). No antibiotics showed synergy with TGC in >10% of the tested isolates. Most isolates with positive checkerboard test also tested positive with time-kill assay for COL (97.6%), but not for TGC (20.0%). Among 57 patients with monobacterial infection caused by the tested CRA isolates, nine (15.8%) received combination regimens with in vitro synergy. All patients…
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