title: Determination of in vitro activities of polymyxin B and rifampin in combination with ampicillin/sulbactam or cefoperazone/sulbactam against multidrug-resistant Acinetobacter baumannii by the E-test and checkerboard methods.
abstract: The aim of this study was to investigate the in vitro activities of polymyxin B (PB) and rifampin (RIF) in combination with ampicillin/sulbactam (AS) or cefoperazone/sulbactam (CS) against 20 multidrug-resistant Acinetobacter baumannii (MDR-AB) isolates by the checkerboard and E-test methods. Fractional inhibitory concentration index (FICI) values were defined as synergy, FICI ≤ 0.5; additivity, 0.5 < FICI ≤ 1.0, indifference, 1.0 < FICI < 4.0; and antagonism, FICI ≥ 4. Synergistic interaction was detected only for the RIF + AS and RIF + CS combinations. While the most frequently detected interaction type for PB + AS or PB + CS combinations was indifference, some showed antagonistic interactions. The detection rate of synergy was significantly higher by the checkerboard than by the E-test method, and the detection rate of indifference was significantly higher by the E-test than by the checkerboard method for RIF + AS combination (P ≤ 0.0001). In addition, no statistically significant difference was detected between the checkerboard and E-test methods for the detection rates of interaction types for any of the other combinations (P > 0.05), except for PB + CS combination for the detection of additivity (P = 0.018). Owing to the high percentage of synergistic interactions between RIF and AS, we considered this combination as an effective therapeutic option for MDR-AB infections.
authors.affiliation: Department of Microbiology and Clinical Microbiology, Medical Faculty of Suleyman Demirel University.
authors.forename: Emel Sesli
authors.initials: ES
authors.lastname: Cetin
authors.forename: Alper
authors.initials: A
authors.lastname: Tekeli
authors.forename: Ayşe Gul
authors.initials: AG
authors.lastname: Ozseven
authors.forename: Ebru
authors.initials: E
authors.lastname: Us
authors.forename: Buket Cicioglu
authors.initials: BC
authors.lastname: Aridogan
mesh_terms: D000151:Acinetobacter Infections / Q000382:microbiology; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods*; D011112:Polymyxin B / Q000494:pharmacology*; D012293:Rifampin / Q000494:pharmacology*; D047090:beta-Lactams / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D011112:Polymyxin B; D012293:Rifampin