Multidrug-resistant Acinetobacter Baumannii Infections Research Articles

Multidrug resistance among Acinetobacter baumannii isolates from Iran: changes in antimicrobial susceptibility patterns and genotypic profile.

Widespread multidrug-resistant Acinetobacter baumannii (MDR-AB) strains have limited therapeutic options for treating intensive care unit (ICU) patients with MDR-AB infection in Iran. We aimed to evaluate MDR-AB diversity and antimicrobial susceptibility in Tehran (Iran) to address the need for feasible and effective control approaches against severe MDR-AB infections. We used amplified fragment length polymorphism (AFLP) and minimum inhibitory concentration (MIC) determinations to compare genotypic diversity and susceptibility patterns of 100 MDR-AB isolates from ICU patients in two medical centers in Tehran (Iran), from 2006 to 2011. Within 5 years, drastic genotypic changes occurred among MDR-AB isolates, and resistance to antimicrobials increased 0-30%. In 2011, 6-100% of isolates were resistant to every agent tested. All isolates remained susceptible to either minocycline or tobramycin, however, MIC50 concentrations against these agents increased. Novel international clone (IC) variants (not IC I-III types) comprised 36% MDR-AB isolates in 2011. The MDR-AB population in Tehran is rapidly changing toward growing resistance to various antimicrobials, including colistin and tigecycline. Although increasing resistance to last-resort antimicrobials is alarming, simultaneous susceptibility of all MDR-AB isolates to some conventional antibiotics highlights the merits of investigating their synergistic activity against extended-spectrum and pandrug resistant A. baumannii. Integrating the novel Iranian MDR-AB IC variants into epidemiologic clonal and susceptibility profile databases can help global efforts toward the control of MDR-AB pandemic.

Clinical evaluation of tigecycline in the treatment of nosocomial infection in a hospital in Taiwan.

Clinical information on tigecycline use in serious nosocomial infections is limited, and the efficacy is uncertain. The aim of this retrospective study was to assess the utilization pattern and the effectiveness of tigecycline in a tertiary medical center in Taiwan. A retrospective study of the clinical and microbiological outcome of all patients treated with tigecycline for at least 72 hours over a 2-year period was conducted in a 730-bed teaching hospital. Data from 133 patients with 149 cases of nosocomial infection were analyzed in this assessment. The mean APACHE II score at the initiation of tigecycline therapy was 22.5 ± 8.8, and the mean duration of treatment was 11.4 ± 5.6 days. Pneumonia was the most frequently diagnosed clinical indication for tigecycline use (113 cases, 76%). An overall positive clinical outcome was observed in 75 cases (50%). Multidrug-resistant Acinetobacter baumannii (MDRAB) is the most common organism for tigecycline therapy (n = 59), with a positive clinical outcome of 38% in tigecycline monotherapy, 66% in dualtherapy, and 17% in triple-therapy (p = 0.031). The most commonly used combining agents with tigecycline to treat MDRAB infections were intravenous colistin, inhaled colistin, and cepoferazone/sulbactam, with positive clinical outcome rates of 53%, 100%, and 80%, respectively. Admission to intensive care unit was identified as a predictive factor for negative clinical outcome. Our pneumonia-dominated study population demonstrated a lower clinical improvement rate of tigecycline compared to previous published data. Tigecycline monotherapy is not recommended for MDRAB infection, but colistin or cephoperazone/ sulbactam combined with tigecycline seemed to yield a good clinical outcome for MDRAB infection.

A review of intravenous minocycline for treatment of multidrug-resistant Acinetobacter infections.

Options for treatment of multidrug-resistant (MDR) Acinetobacter baumannii infections are extremely limited. Minocycline intravenous is active against many MDR strains of Acinetobacter, and Clinical and Laboratory Standards Institute breakpoints exist to guide interpretation of minocycline susceptibility results with Acinetobacter. In addition, minocycline intravenous holds a US Food and Drug Administration indication for treatment of infections caused by Acinetobacter. There is an accumulating amount of literature reporting successful use of minocycline intravenous for treatment of serious MDR Acinetobacter infections, particularly for nosocomial pneumonia. These results, coupled with the generally favorable tolerability of minocycline intravenous, support its use as a viable therapeutic option for treatment of MDR Acinetobacter infections.

Multidrug-resistant Acinetobacter baumannii infection among neonates in a neonatal intensive care unit at a medical center in central Taiwan.

Few studies have focused on multidrug-resistant Acinetobacter baumannii (MDRAB) infection in neonates. The aim of this study was to investigate risk factors for mortality in neonates with MDRAB infection. This retrospective case-series study was conducted at the Children's Hospital of China Medical University, Taichung, Taiwan. All patients hospitalized between January 2010 and December 2013 in the neonatal intensive care unit (NICU) with MDRAB infections were reviewed. A total of 67 isolates from 59 neonatal patients were positive for MDRAB. Of the 67 isolates, 38 were from blood (56.72%), 16 from sputum (23.88%), seven from pus (10.45%), three from ascites (4.48%), two from cerebrospinal fluid (2.99%), and one from pleural fluid (1.49%). There were five episodes of MDRAB clusters consisting of 28 cases during the study period. The mortality rate due to MDRAB sepsis was 20.34% (12/59). The statistically significant risk factors for mortality due to MDRAB infection were being infected with MDRAB within 7 days of admission to the NICU, use of umbilical vein catheters, absolute neutrophil count < 1500/mm(3), platelet count < 100,000/mm(3), and a delay in initiating adequate antibiotic treatment. MDRAB infection is responsible for a high mortality rate among neonates in the NICU, especially in those who have neutropenia or thrombocytopenia. Infection control and appropriateness of the initial antimicrobial agent with colistin play an important role in reducing mortality.

In vivo activity of daptomycin/colistin combination therapy in a Galleria mellonella model of Acinetobacter baumannii infection

Antimicrobial treatment of multidrug-resistant Acinetobacter baumannii (MDR-AB) infections continues to pose significant challenges. With limited options, clinicians have been pushed towards using unorthodox combinations of licensed antibiotics. Although daptomycin/colistin combination appears to be a promising treatment option based on in vitro data, further preclinical work is needed. In this study, the A. baumannii–Galleria mellonella system was employed to study the in vivo efficacy of this combination in order to determine whether it should be explored further for the treatment of MDR-AB infections. The antimicrobial activity of colistin alone and in combination with daptomycin was assessed versus an A. baumannii type strain (ATCC 19606) and a MDR-AB clinical strain (GN2231) isolated in Anhui, China. Synergy studies were performed using the microtitre plate chequerboard assay and time–kill methodology. The in vivo activity of daptomycin/colistin combination was assessed using a G. mellonella larvae model. The combination of daptomycin and colistin was bactericidal against both strains tested. In chequerboard assays, daptomycin was highly active against A. baumannii when combined with colistin [fractional inhibitory concentration index (FICI) of <0.5]. Treatment of G. mellonella larvae infected with lethal doses of A. baumannii resulted in significantly enhanced survival rates when daptomycin was given with colistin compared with colistin treatment alone (P<0.05). This work suggests that daptomycin/colistin combination is highly active against A. baumannii both in vitro and in a simple invertebrate model of infection.

Analysis of risk factors of multi-drug resistant acinetobacter baumannii infection in patients with sepsis

Objective To investigate the clinical characteristics and risk factors of multi-drug resistant (MDR) acinetobacter baumannii (Ab) infection in patients with sepsis in ICU.Methods Retrospectively analyzed clinical data of 856 cases of sepsis admitted in ICU of our hospital from July 2009 to March 2013,who were divided into MDR Ab related sepsis group (179 cases) and non-MDR Ab related sepsis group (control group,677 cases).Mortality rate,hospitalization expenses,organ function injury level and risk factors of death were compared between two groups.Results Mortality rate,48 hours mortality rate and hospitalization cost of MDR Ab related sepsis group were higher than those of control group (P ＜ 0.05).Septic shock,acute kidney injury and bone marrow suppression more likely occurred in MDR Ab related sepsis group (P ＜ 0.05).APACHE Ⅱ score ＞ 25,septic shock and multiple organ dysfunction syndrome (MODS) within 24 h were risk factors of death in MDR Ab related sepsis group (P ＜ 0.05).Conclusions Patients with MDR Ab related sepsis have worse prognosis and spend more in related treatment.It is important to detect risk factors of death and implement targeting treatment early. Key words: Acinetobacter baumannii; Sepsis; Intensive care unit; Risk factors

ABSTRACT 431

Background and aims: Colistin is active against most multidrug-resistant, aerobic Gram-negative bacteria. Aims: The aim of this study is to document the clinical characteristics and outcomes of use of colistin in pediatric patients at a pediatric intensive care unit for the treatment of Ventilator Associated Pneumonia caused by Multi-Drug Resistant Acinetobacter Baumannii. Methods: We reviewed the medical and laboratory records of 5 critically ill children who were treated with colistin for 10 courses between January 2013 and December 2013 at the Pediatric Intensive Care Unit. Results: The median dosage of colistin was 4 mg/kg/d (ranging from 3 to 5 mg/kg/d, IQR 1) and duration of colistin therapy was changing from 10 days to 34 days. Thirty colistin treatment episodes (79%) had a good or partial clinical response and 8 (21%) had a poor clinical response. There was no evidence of neurotoxicity or nephrotoxicity in this study. All episodes responded colistin therapy however 2 patients died due to the septic shock which was not attributable to Multi-Drug Resistant Acinetobacter Baumannii infections. Conclusions: This small cohort study suggests that colistin is well tolerated and efficacious in severe nosocomial Ventilator Associated Pneumonia caused by Acinetobacter Baumannii.

Erratum to: Clinical outcomes of tigecycline alone or in combination with other antimicrobial agents for the treatment of patients with healthcare-associated multidrug-resistant Acinetobacter baumannii infections

Erratum to: Clinical outcomes of tigecycline alone or in combination with other antimicrobial agents for the treatment of patients with healthcare-associated multidrug-resistant Acinetobacter baumannii infections

Synergistic efficacy of meropenem and rifampicin in a murine model of sepsis caused by multidrug-resistant Acinetobacter baumannii

Multidrug-resistant Acinetobacter baumannii becomes an increasing challenge due to the overuse of antibiotics. Combination therapies are considered as effective options to overcome this matter. The present study was to investigate the synergistic activity of meropenem combined with other antibiotics in vitro and in vivo. Checkerboard assay and time-kill assay were performed to study the combination effects in vitro. For the animal model, a murine sepsis model injected with inoculums intraperitoneally was used. Susceptibility test showed that all the twelve strains in this study were resistant to most of the antibiotics except rifampicin. In combination, meropenem plus rifampicin exhibited synergistic activity against six of twelve strains. In the sepsis model, meropenem monotherapy had no therapeutic effect in this model while it can enhance the activity of rifampicin in both survival rate and bacterial clearance from blood. Moreover, combination therapy significantly reduced plasma IL-6 levels compared with rifampicin monotherapy. Pharmacokinetic analysis of rifampicin was also performed in this study. These data above showed that there was synergistic activity between meropenem and rifampicin against multidrug-resistant Acinetobacter baumannii both in vitro and for experimental model of sepsis. It suggested that combining meropenem with rifampicin may be appropriate in treating multidrug-resistant Acinetobacter baumannii infections.

Effects of Carbapenem consumption on the prevalence of Acinetobacter infection in intensive care unit patients

BackgroundThe consumption of carbapenems has increased worldwide, together with the increase in resistant gram negative bacilli. Subsequently, the prevalence of carbapenem-resistant Acinetobacter infections has increased rapidly and become a significant problem particularly in intensive care unit patients. The aim of the present study was to evaluate the changes in the prevalence of Acinetobacter infection by restricting the consumption of carbapenems in intensive care unit patients.MethodsThis study was conducted between May 1, 2011 and February 28, 2013. The amount of carbapenem consumption and the number of patients with multi-drug resistant Acinetobacter baumannii (MDRAB) isolates during the study period were retrospectively obtained from the records of the patients, who were hospitalized in the intensive care unit. The study period was divided into two periods named as: Carbapenem non-restricted period (CNRP) and carbapenem-restricted period (CRP). During CNRP, no restrictions were made on the use of carbapenems. During CRP, the use of carbapenems was not allowed if there was an alternative to carbapenems. Primary Endpoint: MDRAB infection after ICU admission. The definition of nosocomial infections related to Acinetobacter spp. was based on the criteria of the Center for Disease Control (CDC). The correlation between the amount of carbapenem consumption and the number of infections with MDRAB strains between the two periods were evaluated.ResultsDuring the study period, a total of 1822 patients’ (1053 patients in CNRP and 769 patients in CRP) records were evaluated retrospectively. A total of 10.82 defined daily dose (DDD/100 ICU days) of anti-pseudomonal carbapenem were used in CNRP, and this figure decreased to 6.95 DDD/100 ICU days in CRP. In the 8-month CNRP, 42 (3.98%) MDRAB-related nosocomial infections were detected, and 14 (1.82%) infections were detected in CRP (p = 0.012).ConclusionThe prevalence of MDRAB strains isolated in the CNRP was 2.24-fold higher than the prevalence in the CRP. The prevalence of Acinetobacter infections can be reduced by taking strict isolation measures as well as by implementing good antibiotics usage policy.

Multidrug-resistant Acinetobacter baumannii infection in intensive care unit patients in a hospital with building construction: is there an association?

BackgroundAcinetobacter baumannii (A. baumannii) has emerged globally as a significant pathogen in hospitals. It is also present in soil and water. In a previous study, we discovered that the A. baumannii class 2 integron occurred most frequently. Here, we determined whether the A. baumannii class 2 integron is in the soil around our hospital, and if the soil is the cause for increasing numbers of A. baumannii infections in our intensive care unit (ICU) patients.MethodsThis cross-sectional prospective study was conducted in two ICUs at Loghman-Hakim Hospital, Tehran, Iran, from November 2012 to March 2013. Patient, soil, and hospital environment samples were collected. All isolates were identified using standard bacteriologic and biochemical methods. The phenotypes and genotypes were characterized. The standard disc diffusion method was utilized to test antimicrobial susceptibility. Integron identification was performed by multiplex polymerase chain reaction.ResultsA total of 42 A. baumannii clinical strains were isolated, all from patient samples; 65% of the isolated species were classified as class 2 integrons. The strains were 100% resistant to piperacillin, piperacillin-tazobactam, ceftazidime, ceftriaxone, cotrimoxazole, cefepime, ceropenem, and cefotaxime. However, all of the strains were sensitive to polymyxin B. A. baumannii was detected around the lip of one patient.ConclusionsFurther research is necessary to establish a relationship between A. baumannii and soil, (especially in regards to its bioremediation), as well as to determine its importance in nosocomial infections and outbreaks in the ICU.

Transmission electron microscopic morphological study and flow cytometric viability assessment of Acinetobacter baumannii susceptible to Musca domestica cecropin.

Multidrug-resistant (MDR) Acinetobacter baumannii infections are difficult to treat owing to the extremely limited armamentarium. Expectations about antimicrobial peptides' use as new powerful antibacterial agents have been raised on the basis of their unique mechanism of action. Musca domestica cecropin (Mdc), a novel antimicrobial peptide from the larvae of Housefly (Musca domestica), has potently active against Gram-positive and Gram-negative bacteria standard strain. Here we evaluated the antibacterial activity of Mdc against clinical isolates of MDR-A. baumannii and elucidate the related antibacterial mechanisms. The minimal inhibitory concentration (MIC) of Mdc was 4 μg/mL. Bactericidal kinetics of Mdc revealed rapid killing of A. baumannii (30 min). Flow cytometry using viability stain demonstrated that Mdc causes A. baumannii membrane permeabilization in a concentration- and time-dependent process, which correlates with the bactericidal action. Moreover, transmission electron microscopic (TEM) examination showed that Mdc is capable of disrupting the membrane of bacterial cells, resulting in efflux of essential cytoplasmic components. Overall, Mdc could be a promising antibacterial agent for MDR-A. baumannii infections.

Multidrug-resistant Acinetobacter baumannii infection in the intensive care unit.

We read the report entitled Multidrug-resistant Acinetobacter baumannii infection in intensive care unit patients in a hospital with building construction: is there an association? [1] with great interest. In this report, Kamalbeik et al. [1] concluded that further research is necessary to establish a relationship between A. baumannii and soil, (especially in regards to its bioremediation). In fact, there have been many reports of A. baumannii within hospitals in many settings worldwide [1,2,3]. Outbreaks in intensive care units are important considerations and should be a focus of postoperative infection control [1,4]. The source of an infectious outbreak in the intensive care unit is usually unexpected and may include uncommon sources such as contaminated medical apparatus [4]. The role of the anesthesiologist is to promote good clinical practice according to infection control principles. Routine surveillance for possible contamination of medical apparatuses is also suggested.

Antimicrobial Blue Light Therapy for Multidrug-Resistant Acinetobacter baumannii Infection in a Mouse Burn Model: Implications for Prophylaxis and Treatment of Combat-related Wound Infections

In this study, we investigated the utility of antimicrobial blue light therapy for multidrug-resistant Acinetobacter baumannii infection in a mouse burn model. A bioluminescent clinical isolate of multidrug-resistant A. baumannii was obtained. The susceptibility of A. baumannii to blue light (415 nm)-inactivation was compared in vitro to that of human keratinocytes. Repeated cycles of sublethal inactivation of bacterial by blue light were performed to investigate the potential resistance development of A. baumannii to blue light. A mouse model of third degree burn infected with A. baumannii was developed. A single exposure of blue light was initiated 30 minutes after bacterial inoculation to inactivate A. baumannii in mouse burns. It was found that the multidrug-resistant A. baumannii strain was significantly more susceptible than keratinocytes to blue light inactivation. Transmission electron microscopy revealed blue light-induced ultrastructural damage in A. baumannii cells. Fluorescence spectroscopy suggested that endogenous porphyrins exist in A. baumannii cells. Blue light at an exposure of 55.8 J/cm(2) significantly reduced the bacterial burden in mouse burns. No resistance development to blue light inactivation was observed in A. baumannii after 10 cycles of sublethal inactivation of bacteria. No significant DNA damage was detected in mouse skin by means of a skin TUNEL assay after a blue light exposure of 195 J/cm(2).

Risk factors for acquisition of multidrug-resistant Acinetobacter baumannii among cancer patients

Data regarding multidrug-resistant (MDR) Acinetobacter baumannii infections among cancer patients are limited. We conducted a case-control study to investigate the risk factors for acquisition of MDR A baumannii and the outcomes among cancer patients. Cases were inpatients with malignancy who had MDR A baumannii from any cultures between 2008 and 2011. Controls were inpatients with malignancy but no MDR A baumannii. A total of 31 case patients were matched with 62 control patients. Hematologic malignancy (P = .036), need for dialysis (P = .01), admission for other reasons except elective surgery (P = .03), transfer from other health care facilities (P = .02), prolonged intensive care unit stay (P = .004), mechanical ventilation (P < .001), pressor use (P = .001), tube feeding (P < .001), transfusion (P = .009), and prior antimicrobial use (P < .001) were identified as significant risk factors in univariate analysis. Need for dialysis (odds ratio [OR], 18.23; P = .04) and prolonged intensive care unit stay (OR, 19.28; P = .01) remained significant in multivariate analysis. Lengths of stay were 28 days for the case patients and 10 days for the control patients (P = .001). The 90-day mortality rates were 41.9% and 29.0%, respectively (P = .20). Acquisition of MDR A baumannii among cancer patients appears to be associated with general nosocomial infection risk factors rather than underlying malignancies.

Emergence of Rifampicin, Tigecycline, and Colistin-ResistantAcinetobacter baumanniiin Iran; Spreading of MDR Strains of Novel International Clone Variants

Multidrug-resistant Acinetobacter baumannii infections are serious challenges for clinicians because of A. baumannii propensity to acquire resistance to a wide spectrum of antimicrobial agents. In this study, 91 A. baumannii isolates from patients in tertiary intensive care units of three university hospitals in the north, central, and south of Iran were selected and tested for susceptibility to 22 antimicrobials; amplified restriction fragment polymorphism and multiplex polymerase chain reaction methods were used to determine genetic relationships and International Clone (IC) of A. baumannii isolates, respectively. Twenty-four genotypes were identified in A. baumannii isolates. About 91.2% of isolates categorized into 4 distinct clusters; one was more heterogeneous and observed across the three locations. A considerable number of the isolates (27.5%) belonged to the novel IC variant, sequence group 7 (SG7), which was geographically widespread in three locations. The drug resistance pattern showed that 14.2%, 20%, and 77% of the A. baumannii isolates were resistant to colistin, tigecycline, and rifampicin, respectively. Nine percent of isolates (8) showed simultaneous resistance to colistin, rifampicin, and tigecycline. Interestingly, all of them were susceptible to ampicillin-sulbactam and/or tobramycin. According to our results, SG7 could be considered as a pan-Iranian clone.

Clinical outcomes of tigecycline alone or in combination with other antimicrobial agents for the treatment of patients with healthcare-associated multidrug-resistant Acinetobacter baumannii infections

Tigecycline (TG) has been shown to be active in vitro against Acinetobacter baumannii, although data on the clinical efficacy of TG alone or in combination for the treatment of infections due to multidrug-resistant A. baumannii (MDRAB) remain limited. The purpose of this study was to investigate the clinical outcomes of patients with healthcare-associated infections (HAIs) caused by MDRAB who were treated with imipenem/cilastatin and sulbactam, and TG alone or in combination with other antibiotics. A total of 386 patients with HAIs caused by MDRAB were retrospectively analyzed and grouped into TG and non-TG groups, depending on whether they received TG treatment. Of the 266 patients in the TG group, 108 were treated with TG alone and 158 were treated with TG in combination with ceftazidime, ceftriaxone, piperacillin/tazobactam, or a carbapenem. All 120 patients in the non-TG group were treated with imipenem/cilastatin and sulbactam. The primary outcome measure was 30-day mortality after TG treatment and the secondary outcome was clinical outcome. There were no significant differences in survival rates between the two groups. However, the rate of unfavorable outcome was significantly lower (p < 0.05) among patients in the TG group than among patients in the non-TG group. The most significant predictor of unfavorable outcome was sepsis, whereas TG treatment and microbial eradication were the most significant predictors of favorable outcomes. Our study represents the largest study of patients with MDRAB infection treated with TG and expands our understanding of the role of TG therapy alone or in combination with other agents for the treatment of HAI caused by MDRAB.

Treating multidrug-resistant Acinetobacter baumannii infection by blocking its virulence factors

Acinetobacter baumannii is one of the most prevalent causes of severe hospital-acquired infections, such as ventilator-associated pneumonia, bacteremia and meningitis, among others, with a high rat...

Erradicación de un brote nosocomial de infecciones por Acinetobacter baumannii multirresistente tras el ajuste de cargas de trabajo y refuerzo de precauciones específicas

IntroductionDuring 2009, an outbreak of multidrug-resistant Acinetobacter baumannii (MDR A. baumannii) infections was detected in a 27-bed intensive care unit, resulting in 25 cases being infected. MethodsA matched case-control study was conducted to identify risk factors for infection. The colonization pressure, or the proportion of other patients colonized by MDR A. baumannii, was estimated. TISS-28 and Omega scores of each patient were calculated to evaluate nursing work requirements. Conditional logistic regression analyses were carried out. ResultsBreakdowns in hand washing and glove use were observed. Infected patients (cases) were more likely than paired controls to have had longer exposure to invasive devices and antimicrobial treatment. The independent risk factors identified by the multivariate analysis were, mechanical ventilation [odds ratio (OR)=1.03; 95% confidence interval (CI), 1.01-1.05; P=.01], and exposure to an infected or colonized patient [OR=1.7; 95%CI, 1.1-2.6; P=.02). A combined infection control strategy was implemented, including strict compliance with isolation precautions, grouping of patients, reinforcing cleaning and disinfection of surfaces, and a decrease in work load. Subsequently, a sharp reduction in the incidence MDR A. baumannii infections was shown. Therapeutic activity scores were significantly higher for cases than for controls. ConclusionThe results suggest patient-to-patient transmission of MDR A. baumannii. Reinforcement of specific procedures and work load adjustment were essential to eradicate this outbreak.

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

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.