Evaluation of antibiotic synergy against Acinetobacter baumannii: a comparison with Etest, time-kill, and checkerboard methods

• Published in: Diagnostic microbiology and infectious disease Vol. 38; no. 1; pp. 43 - 50
• Main Authors: Bonapace, Charles R, White, Roger L, Friedrich, Lawrence V, Bosso, John A
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.09.2000; Elsevier
• Subjects: Acinetobacter - drug effects; Acinetobacter Infections - drug therapy; Anti-Bacterial Agents - pharmacology; Anti-Infective Agents - pharmacology; Antibacterial agents; Antibiotics. Antiinfectious agents. Antiparasitic agents; Biological and medical sciences; Cefepime; Cephalosporins - pharmacology; Drug Synergism; Drug Therapy, Combination - pharmacology; Fluoroquinolones; Humans; Medical sciences; Microbial Sensitivity Tests; Naphthyridines - pharmacology; Penicillins - pharmacology; Pharmacology. Drug treatments; Piperacillin - pharmacology; Reproducibility of Results; Tobramycin - pharmacology; Drug combination; Cefepime; β-Lactams; Neisseriaceae; In vitro; Synergism; Biological activity; Penicillin derivatives; Acinetobacter baumannii; Antibiotic; Cephalosporin derivatives; Piperacillin; Bacteria; Micrococcales; Tobramycin; Antibacterial agent; Clinical isolate
• ISSN: 0732-8893; 1879-0070
• DOI: 10.1016/S0732-8893(00)00163-2

Acinetobacter baumannii is becoming increasingly resistant to antibiotics, often requiring combination therapy. Numerous methods exist to detect the presence of in vitro synergy with the time-kill and checkerboard tests being widely used. The Epsilometer test (E test) is a new method that is less labor intensive, but has not been evaluated using a wide range of antimicrobials and organisms. We assessed synergy using the time-kill and checkerboard tests and compared the results to the E test method using 10 clinical isolates of A. baumannii. Antimicrobial combinations evaluated consisted of trovafloxacin or tobramycin in combination with cefepime or piperacillin. Synergy was detected with all combinations by either the checkerboard or time-kill method. Synergy was not detected by the Etest method. The agreement between the time-kill test and Etest method was 72% (range 42–97%); for the time-kill and checkerboard tests, agreement was 51% (range 30–67%). The Etest method appears promising although further testing should be performed with additional antimicrobial agents and organisms.