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.

Objective: 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.

Conclusions: 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.