Determination of In Vitro Activities of Polymyxin B and Rifampin in Combination with Ampicillin/Sulbactam or Cefoperazone/Sulbactam against Multidrug-Resistant <i>Acinetobacter baumannii</i> by the E-test and Checkerboard Methods

Abstract

SUMMARY: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 Ã 0.5; additivity, 0.5 º FICI Ã 1.0, indifference, 1.0 º FICI º 4.0; and antagonism, FICI AE 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 Ã 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 À 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.

Synergistic Antimicrobial Activity of Camellia sinensis and Juglans regia against Multidrug-Resistant Bacteria

“…The FICI results were interpreted as follows: < 0.5 synergy; 0.5 to 1 additive effect; 1–2 indifferent or no effect; and >2 antagonism [19]. Synergistic combinations were further checked using the Etest/agar incorporation assay [20] in which an Etest-strip of each respective antimicrobial agent was placed on MH agar plates containing FIC and 0.5 x FIC of each extract. MH plates containing no antimicrobial agent or extract served as growth control.…”

A meta-analysis of in vitro antibiotic synergy against Acinetobacter baumannii

“…In one of them, one antibiotic has been previously incorporated into the agar plate and the other antibiotic is provided by the strip (Gordon, Png and Wareham, 2010, Wareham and Bean, 2006, Wareham, Gordon and Hornsey, 2011) (This method is referenced in Table 1 as one strip). In another way, the two strips are applied at right angles to each other, intersecting at the MIC of each agent tested (Cetin, Tekeli, Ozseven, Us and Aridogan, 2013, Pankey and Ashcraft, 2009, Tan, Ng, Tan and Huang, 2007, Wareham and Bean, 2006) (This method is referenced in Table 1 as two strips). In the third way, after spreading the bacteria onto agar plates, one strip is placed onto the agar and incubated for one hour.…”

“…Synergy as ∑FIC≤0.5; indifference as 2≥∑FIC>0.5 and antagonism as ∑FIC≥2 (Karaoglan, Zer, Bosnak, Mete and Namiduru, 2013), or 4. Synergy as ∑FIC≤0.5; additive as 1≥∑FIC>0.5; indifference as 4>∑FIC>1 and antagonism as ∑FIC≥4 (Cetin, Tekeli, Ozseven, Us and Aridogan, 2013). …”

“…On the other hand, gradient diffusion methods are easy to perform and, hence, available to routine clinical laboratories; in this way, these methods have been suggested as an alternative and convenient method for synergy testing(Cetin, Tekeli, Ozseven, Us and Aridogan, 2013). It is worth to mention that antibacterial combination methods are not fully standardized, and there is no single clear definition for synergy in the studies included in this review.…”

In vitro assessment of cefoperazone-sulbactam based combination therapy for multidrug-resistant Acinetobacter baumannii isolates in China

“…In addition, β-lactamase inhibitors, including sulbactam and tazobactam, are also effective in treating MDRAB infections (18). Moreover, rifampicin and cefoperazonesulbactam in combination have synergistic effects against A. baumannii infections (19). The aim of the present study was to investigate the efficacy of cefoperazone-sulbactam combined with either tigecycline or rifampicin against clinical isolates of A. baumannii.…”