# Salvage Therapy Against Infections of MDR Acinetobacter baumannii Achieved by Synergistic Effect of Colistin-Containing Therapies—Preliminary Study

## TL;DR

This study explores combining colistin with other antibiotics to treat infections caused by drug-resistant Acinetobacter baumannii, showing promising synergistic effects.

## Contribution

The study identifies synergistic and additive antibiotic combinations with colistin for treating multi-drug-resistant A. baumannii.

## Key findings

- Colistin combined with ampicillin/sulbactam showed synergistic activity against two MDR A. baumannii strains.
- Combining colistin with carbapenems, aminoglycosides, or tigecycline resulted in additive effects.
- Synergistic combinations reduced antibiotic MICs by 8- to 128-fold, potentially lowering colistin toxicity.

## Abstract

Infections caused by multi-drug-resistant Acinetobacter baumannii are a global threat. The World Health Organization has recognized carbapenem-resistant A. baumannii as critical pathogens for which further research and development of effective drugs are needed. The aim of this study was to identify antibiotic combinations with possible potential for additive or synergistic action with colistin, and thus to find new therapeutic possibilities for the treatment of infections caused by multi-drug-resistant A. baumannii. The research involved the two multi-drug-resistant A. baumannii strains isolated from hospitalized patients. In this study, six antibiotics were chosen to combine with colistin: amikacin, gentamicin, ampicillin/sulbactam, tigecycline, imipenem, and meropenem. For both strains, the synergistic activity of colistin and ampicillin/sulbactam was demonstrated, and additive activity for ABA25, colistin, and meropenem or imipenem. The MICs of antibiotics that showed synergism with colistin were reduced by 8- to 128-fold. Additive interactions have been shown in colistin combination with carbapenems, aminoglycosides, and tigecycline. The results prove the synergistic effect of the tested antibiotics, which may be helpful in the selection of potentially effective multi-drug therapies and their application in clinical practice, which may involve reducing the doses of colistin in therapy and its toxicity.