Investigating the in vitro synergistic activities of several antibiotic combinationsagainst carbapenem-resistant Acinetobacter baumannii isolates

Combinations of Antibiotics Effective against Extensively- and Pandrug-Resistant Acinetobacter baumannii Patient Isolates

Infections due to drug-resistant Acinetobacter baumannii strains are increasing and cause significant morbidity and mortality, especially in hospitalized and critically ill patients. A. baumannii rapidly develops resistance to numerous antibiotics, and antibiotics traditionally used against this deadly pathogen have been failing in recent years, highlighting the need to identify new treatment strategies. Treatment options that have shown promise include revisiting common antibiotics not typically used against A. baumannii, evaluating new antibiotics recently introduced to market, and identifying combinations of antibiotics that display synergistic interactions. In this study, we characterized the antibiotic susceptibility profiles of extensively (XDR) and pandrug-resistant (PDR) A. baumannii patient isolates. We examined the potency of 22 standard-of-care antibiotics and the newer antibiotics eravacycline, omadacycline, and plazomicin against these strains. Furthermore, we examined combinations of these antibiotics against our collection to identify synergistic effects. We found that this collection is highly resistant to most or all standard-of-care antibiotics, except for minocycline and rifampin. We show that eravacycline and omadacycline are effective against these strains based on minimum inhibitory concentrations. We also identified two highly effective combinations, cefepime and amikacin and cefepime and ampicillin-sulbactam, which exhibited high rates of synergy against this collection. This information is valuable in our battle against highly drug resistant and virtually untreatable A. baumannii infections.

In-vitro evaluation of different antimicrobial combinations with and without colistin against carbapenem-resistant Acinetobacter baumannii clinical isolates

BACKGROUND

Carbapenem-resistant Acinetobacter baumannii (CRAB) infections are one of the most common causes of nosocomial infections and have high mortality rates due to difficulties in treatment. In this study, the in vitro synergistic interactions of the colistin (CT)-meropenem (MEM) combination and patient clinical outcomes were compared in CRAB-infected patients that receive CT-MEM antimicrobial combination therapy. In addition, in vitro synergistic interactions of MEM-ertapenem (ETP), MEM-fosfomycin (FF) and CT-FF antimicrobial combinations were investigated. Finally, the epsilometer (E) test and checkerboard test results were compared and the compatibility of these two tests was evaluated.

METHODS

Twenty-one patients were included in the study. Bacterial identification was performed with MALDI-TOF, and antimicrobial susceptibility was assessed with an automated system. Synergy studies were performed using the E test and checkerboard method.

RESULTS

For the checkerboard method, the synergy rates for CT-MEM, MEM-FF, MEM-ETP and CT-FF were 100%, 52.3%, 23.8% and 28.5%, respectively. In the E test synergy tests, synergistic effects were detected for two isolates each in the CT-MEM and CT-FF combinations. Microbial eradication was achieved in nine (52.9%) of the 17 patients that received CT-MEM combination therapy. The agreement between the E test and the checkerboard test was 6.5%.

CONCLUSIONS

A synergistic effect was found with the checkerboard method for the CT-MEM combination in all isolates in our study, and approximately 70% of the patients benefited from treatment with this combination. In addition, more than half of the isolates showed a synergistic effect for the MEM-FF combination. Combinations of CT-MEM and MEM-FF may be options for the treatment of CRAB infections. However, a comprehensive understanding of the potential of the microorganism to develop resistant mutants under applied exposures, as well as factors that directly affect antimicrobial activity, such as pharmacokinetics/pharmacodynamics, is essential for providing treatment advice. We found a low rate of agreement between the E test method and the checkerboard test method in our study, in contrast to the literature. Comprehensive studies that compare clinical results with methods are needed to determine the ideal synergy test and interpretation method.

Evaluation of synergistic activity of antibiotic combinations in extensive drug-resistant Acinetobacter species using checkerboard assay

Introduction. Acinetobacter is one of the challenging drug-resistant organisms that can endanger patients' lives if not treated properly.Aim. This study was designed to investigate the activity of three synergistic antimicrobial combinations against extensive drug-resistant Acinetobacter isolates; ampicillin/sulbactam plus amikacin, ampicillin/sulbactam plus ciprofloxacin, and meropenem plus amikacin.Methodology. Minimum inhibitory concentrations of 100 XDR-Acinetobacter isolates were determined using the Vitek2 system. The broth micro-dilution method was performed to determine tigecycline MIC. Checkerboard assay was used to evaluate in vitro activity of the three antibiotic combinations.Results. MIC results by the Vitek 2C system revealed that all Acinetobacter isolates were resistant to all tested antibiotics except for colistin against which no resistance was reported. As for tigecycline, all isolates were susceptible. Regarding MIC results of each antibiotic, all isolates were resistant to meropenem and ciprofloxacin. While 95 % of isolates were resistant to both ampicillin/sulbactam and amikacin. The activities of antibiotic combinations by checkerboard assay were as follows: ampicillin/sulbactam plus amikacin was synergic in 52 %, additive 40 % and indifferent in 8 % of isolates, ampicillin/sulbactam plus ciprofloxacin was synergic in 40 %, additive 46 % and indifferent in 14 % of isolates, meropenem/amikacin combination was synergic in 22 %, additive in 49 % of isolates and indifferent in 29 % of isolates. No antagonistic activity was detected against any of the tested antibiotic combinations.Conclusion. Ampicillin/sulbactam plus amikacin showed the highest synergistic activity followed by ampicillin/sulbactam plus ciprofloxacin. This reflects the value of adding aminoglycosides to either of a β-lactam or quinolone. The tested antibiotic combinations are promising treatment options for XDR-Acinetobacter.

In search for a synergistic combination against pandrug-resistant A. baumannii; methodological considerations

PURPOSE

Pending approval of new antimicrobials, synergistic combinations are the only treatment option against pandrug-resistant A. baumannii (PDRAB). Considering the lack of a standardized methodology, the aim of this manuscript is to systematically review the methodology and discuss unique considerations for assessing antimicrobial combinations against PDRAB.

METHODS

Post-hoc analysis of a systematic review (conducted in PubMed and Scopus from inception to April 2021) of studies evaluating antimicrobial combination against A. baumannii, based on antimicrobials that are inactive in vitro alone.

RESULTS

Eighty-four publications were reviewed, using a variety of synergy testing methods, including; gradient-based methods (n = 11), disk-based methods (n = 6), agar dilution (n = 2), checkerboard assay (n = 44), time-kill assay (n = 50), dynamic in vitro PK/PD models (n = 6), semi-mechanistic PK/PD models (n = 5), and in vivo animal models (n = 11). Several variations in definitions of synergy and interpretation of each method were observed and are discussed. Challenges related to testing combinations of antimicrobials that are inactive alone (with regards to concentrations at which the combinations are assessed), as well as other considerations (assessment of stasis vs killing, clinical relevance of re-growth in vitro after initial killing, role of in vitro vs in vivo conditions, challenges of clinical testing of antimicrobial combinations against PDRAB infections) are discussed.

CONCLUSION

This review demonstrates the need for consensus on a standardized methodology and clinically relevant definitions for synergy. Modifications in the methodology and definitions of synergy as well as a roadmap for further development of antimicrobial combinations against PDRAB are proposed.

Systematic Review of Antimicrobial Combination Options for Pandrug-Resistant Acinetobacter baumannii

Antimicrobial combinations are at the moment the only potential treatment option for pandrug-resistant A. baumannii. A systematic review was conducted in PubMed and Scopus for studies reporting the activity of antimicrobial combinations against A. baumannii resistant to all components of the combination. The clinical relevance of synergistic combinations was assessed based on concentrations achieving synergy and PK/PD models. Eighty-four studies were retrieved including 818 eligible isolates. A variety of combinations (n = 141 double, n = 9 triple) were tested, with a variety of methods. Polymyxin-based combinations were the most studied, either as double or triple combinations with cell-wall acting agents (including sulbactam, carbapenems, glycopeptides), rifamycins and fosfomycin. Non-polymyxin combinations were predominantly based on rifampicin, fosfomycin, sulbactam and avibactam. Several combinations were synergistic at clinically relevant concentrations, while triple combinations appeared more active than the double ones. However, no combination was consistently synergistic against all strains tested. Notably, several studies reported synergy but at concentrations unlikely to be clinically relevant, or the concentration that synergy was observed was unclear. Selecting the most appropriate combinations is likely strain-specific and should be guided by in vitro synergy evaluation. Furthermore, there is an urgent need for clinical studies on the efficacy and safety of such combinations.

In-vitro synergistic activity of colistin and meropenem against clinical isolates of carbapenem resistant E.coli and Klebsiella pneumoniae by checkerboard method

CONTEXT

The emergence of drug resistant pathogens pose major threat to hospitalized patients as well as to the community associated with increased mortality and morbidity. The treatment of carbapenem resistant enterobacteriaceae, one of the top WHO priority pathogen remains a global issue. Combination therapy with different classes of antibiotics have been tried with the aim to reduce toxicity, to increase the efficacy of the drugs and to reduce resistance. The in-vitro synergy methods have to be carried out to determine whether the combination of those antibiotics are synergistic, antagonistic or additive.

AIMS

We have performed in-vitro synergy testing by checkerboard method for colistin -meropenem combination to determine whether the combination of the two antibiotics were synergistic or antagonistic.

METHODS AND MATERIAL

All the consecutive twenty five blood isolates of Escherichia coli and twenty five blood isolates of Klebsiella pneumoniae which were showing resistance to carbapenems by either disc diffusion or vitek 2 were collected over a period of 6 months and checkerboard method was performed.

STATISTICAL ANALYSIS USED

The reduction of MIC of colisin on combination with meropenem compared to MIC of colistin alone is analyzed by McNemar's chisquare test with the help of software Stata version 14 and p value < 0.05 is considered as significant.

RESULTS

56% of K. pneumoniae showed synergy and 44% showed additive/indifference results. For E. coli 40% showed synergy and 60% showed additive/indifference. None of the isolates of E. coli and K. pneumoniae showed antagonism. There was more than two fold reduction in MIC of colistin (significant) on combining withmeropenem.

CONCLUSIONS

The study results support the combination therapy to treat infections by multi-drug-resistant Klebsiela pneumoniae and Escherichia coli by in-vitro checkerboard testing method which inturn will be helpful for clinicians for judicious use of antimicrobials.

Global prevalence of colistin resistance in clinical isolates of Acinetobacter baumannii: A systematic review and meta-analysis

INTRODUCTION

Acinetobacter baumannii antimicrobial resistance is a public health concern in developing and developed countries, especially in the hospital setting. Understanding the antibiotic resistance profile can help to provide better guidelines for the prescription of appropriate antibiotics, reduction of antibiotic resistance, and introducing new and effective treatment options.

METHOD

Using the PRISMA guidelines, databases of PubMed, Embase, and Cochrane Library were searched systematically from January 1, 2000, to January 1, 2018. All statistical analyses were carried out via Comprehensive Meta-Analysis Software Version 2.0 (Biostat, Englewood, NJ). Depending on the heterogeneity test, either random or fix effect models were used for determining the pooled prevalence of drug resistance.

RESULT

A total of 150 studies were included from 41 countries of six different WHO regional offices worldwide. The highest and the lowest rate of resistance were observed for cefotaxime (99%, 95% CI: 95-99.9) in Africa and colistin (1.1%, 95% CI: 0.3-4.5) in Western Pacific, respectively. Lebanon (17.5%, 95% CI: 16-19) and China (12%, 95% CI: 3.5-32.5) had the highest and Germany (0.2%, 95% CI: 0-2.5) had the lowest rate of resistance for colistin.

CONCLUSION

Our analysis showed that prevalence and rate of increased colistin resistance in South-East Asia and Eastern Mediterranean countries are higher than other regions of the world. Therefore, the establishment of appropriate antibiotic usage guidelines should be essential in these countries.

Carbapenem-resistant Acinetobacter baumannii and Pseudomonas aeruginosa: characterization of carbapenemase genes and E-test evaluation of colistin-based combinations

Background

Carbapenamase producing Acinetobacter baumannii and Pseudomonas aeruginosa are emerging worldwide limiting the use of carbapenems as effective and safe drugs.

Purpose

To characterize different carbapenemase genes carried by carbapenem-resistant (CR) A. baumannii and P. aeruginosa isolates and to evaluate the in vitro effect of some colistin-based combinations by E-test method in Zagazig University Hospitals ICU isolates.

Methods

CR A. baumannii and P. aeruginosa isolated from the surgical intensive care unit (ICU) were tested for carbapenemase genes by polymerase chain reaction and the effect of colistin/meropenem and colistin/tigecycline combinations was evaluated by E-test.

Results

Genes coding for OXA-23, NDM and GES were detected in 90, 66.7 and 50% of CR A. baumannii, respectively, while genes coding for VIM, GES, NDM and IMP were detected in 50, 40.9, 27.3 and 18.2% of CR P. aeruginosa, respectively. Colistin/tigecycline combination showed synergistic and additive effect in 20% and 60% of A. baumannii isolates, respectively, while colistin/meropenem combination showed synergistic and additive effect in 63.6% and 36.4% of P. aeruginosa, respectively.

Conclusion

Carbapenemase genes carriage accounts for high level carbapenem resistance in our isolates. Colistin/tigecycline and colistin/meropenem combinations can be considered for treatment of severe infections by CR A. baumannii and P. aeruginosa, respectively.

Synergy effect of meropenem-based combinations against Acinetobacter baumannii: a systematic review and meta-analysis

PURPOSE

The main objective of our meta-analysis was to examine the in vitro synergistic effect of meropenem-based combination therapies against Acinetobacter baumannii through a systematic review of the existing literature.

METHODS

An extensive search was performed with no restrictions on date of publication, language, and publication type. Our study evaluated the main conclusions drawn from various studies describing the synergistic activity of combination therapies in vitro.

RESULTS

In this review, 56 published studies were included. Our report included data on 20 types of antibiotics combined with meropenem in 1,228 Acinetobacter baumannii isolates. In time-kill studies, meropenem combined with polymyxin B and rifampicin showed synergy rates of 98.3% (95% CI, 83.7%-100.0%) and 89.4% (95% CI, 57.2%-100.0%), respectively, for Acinetobacter baumannii, modest synergy rates were found for meropenem combined with several antibiotics such as colistin and sulbactam, and no synergy effect was displayed in the combination of meropenem and ciprofloxacin, whereas in checkerboard method, the synergy rates of polymyxin B and rifampicin were 37.0% (95% CI, 0.00%-100.0%) and 56.3% (95% CI, 8.7%-97.8%), respectively.

CONCLUSION

We found that time-kill studies generally identified the greatest synergy, while checkerboard and Etest methods yielded relatively poor synergy rates. Further well-designed in vivo studies should be carried out to confirm these findings.