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. 2025 Oct;113(2):116888.
doi: 10.1016/j.diagmicrobio.2025.116888. Epub 2025 May 10.

In vitro activity of amikacin combined with meropenem, colistin and ceftazidime/avibactam against genetically distinct multidrug-resistant K. pneumoniae, A. baumannii and S. marcescens isolates using three methods

Saidy Vásconez Noguera  1 , Marina Farrel Côrtes  2 , Ana Paula Marchi  2 , Joyce Vanessa Fonseca  2 , Flavia Rossi  3 , Cláudia Maria Dantas de Maio Carrilho  4 , Anna Sara Levin  5 , Silvia Figueiredo Costa  6 , Lauro Vieira Perdigão Neto  2
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In vitro activity of amikacin combined with meropenem, colistin and ceftazidime/avibactam against genetically distinct multidrug-resistant K. pneumoniae, A. baumannii and S. marcescens isolates using three methods

Saidy Vásconez Noguera et al. Diagn Microbiol Infect Dis. 2025 Oct.

Abstract

Purpose: To evaluate in vitro efficacy of amikacin combined with meropenem, colistin, and ceftazidime/avibactam against diverse multidrug-resistant isolates of K. pneumoniae (n = 40), A. baumannii (n = 20), and S. marcescens (n = 12), using three methods.

Methods: Antimicrobial combinations were tested via Epsilometer strip crossing, disk approximation, and time-kill assays.

Results: Amikacin combined with colistin and ceftazidime/avibactam showed synergy in 70,0 % (28/40) and 75,0 % (9/12) of K. pneumoniae and S. marcescens isolates. Meropenem showed limited activity in 25,0 % (5/20) of A. baumannii isolates. Minor errors were observed in <50,0 % of isolates, notably with a 25,0 % error rate for amikacin and colistin using disk approximation. Presence of aminoglycoside-modifying enzyme (AMEs) and blaOXA-23 genes in A. baumannii, and AMEs and ESBL genes in Enterobacterales showed low synergy.

Conclusion: Amikacin combined with colistin and ceftazidime/avibactam showed promise against Enterobacterales MDR infections but limited efficacy against Acinetobacter, influenced by resistance genes. E-test can be useful for routine laboratory.

Keywords: Disk approximation; Epsilometer test; Gram-negative; In vitro synergy; Multidrug-resistant; Time-kill.

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Conflict of interest statement

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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