# P-1305. Evaluation of In Vitro Synergistic Activity of Antimicrobial Combinations against Carbapenem-Resistant Acinetobacter baumannii

## TL;DR

This study tests antibiotic combinations against drug-resistant Acinetobacter baumannii and finds that some combinations are highly effective in stopping bacterial growth in lab tests.

## Contribution

The study evaluates multiple antimicrobial combinations for synergy against CRAB using in vitro methods, providing evidence for potential treatment strategies.

## Key findings

- Polymyxin B + Sulbactam and Polymyxin B + Meropenem + Sulbactam showed 100% synergy against CRAB isolates.
- Sulbactam + Tigecycline and Sulbactam + Polymyxin B were highly effective with 98.33% synergy.
- Sulbactam + Avibactam was the least effective combination with only 65% synergy.

## Abstract

Carbapenem-resistant Acinetobacter baumannii (CRAB) presents a significant healthcare concern owing to restricted treatment alternatives and elevated mortality rates. This study assesses the in vitro synergistic effects of antimicrobial combinations to determine appropriate treatment alternatives.Table 1In Vitro Synergistic Activity of Antimicrobial Combinations

In Vitro Synergistic Activity of Antimicrobial Combinations

Sixty non-duplicate CRAB isolates were identified and tested using the VITEK 2 system. Resistance mechanisms were determined via PCR for blaNDM and blaOXA-48. Synergistic activity of Polymyxin B (PB) + Sulbactam (SUL), Tigecycline (TGC) + SUL, Minocycline (MIN) + SUL, Sulbactam + Avibactam (SUL-AVI), and PB + Meropenem (MEM) + SUL was assessed using the Broth Disk Elution (BDE) method.

A total of 60 clinical isolates were tested for in vitro synergy using different antibiotic combinations. Effectiveness was defined as no bacterial growth (-) in the presence of a drug combination. The most effective combinations were SUL+PB and SUL+PB+MEM, showing 100% synergy (no bacterial growth). SUL+TGC and SUL+PB were highly effective (98.33%, CI: 95.09%-101.57%), followed by SUL+MIN (91.67%, CI: 84.67%-98.66%). SUL+AVI was the least effective (65%, CI: 52.93%-77.07%) [Table 1]. Chi-square analysis showed no significant difference between SUL+TGC, SUL+PB, and SUL+PB+MEM (p > 0.05). Advanced pairwise Z-tests also found no statistically significant differences among combinations (all p-values > 0.05).

Polymyxin B-based regimens, particularly in combination with Meropenem and Sulbactum, appear highly promising for use in critically ill patients where rapid, broad-spectrum activity is paramount.

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