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

Abstract Background 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 Methods 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. Results 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). Conclusion 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. Disclosures All Authors: No reported disclosures