In vitro activity of apramycin (EBL-1003) in combination with colistin, meropenem, minocycline or sulbactam against XDR/PDR Acinetobacter baumannii isolates from Greece.

OBJECTIVES: To evaluate the in vitro activity of the combination of apramycin with colistin, meropenem, minocycline or sulbactam, against some well-characterized XDR Acinetobacter baumannii clinical isolates from Greece, to understand how apramycin can be best incorporated into clinical practice and optimize effectiveness. METHODS: In vitro interactions of apramycin (0.5×, 1× and 2× the MIC value) with colistin (2†mg/L), meropenem (30†mg/L), minocycline (3.5†mg/L) or sulbactam (24†mg/L) were tested using time-kill methodology. Twenty-one clinical A. baumannii isolates were chosen, exhibiting apramycin MICs of 4-16†mg/L, which were at or below the apramycin preliminary epidemiological cut-off value of 16†mg/L. These isolates were selected for a range of colistin (4-32†mg/L), meropenem (16-256†mg/L), minocycline (8-32†mg/L) and sulbactam (8-32†mg/L) MICs across the resistant range. Synergy was defined as a ≥2†log10†cfu/mL reduction compared with the most active agent. RESULTS: The combination of apramycin with colistin, meropenem, minocycline or sulbactam was synergistic, at least at one of the concentrations of apramycin (0.5×, 1× or 2× MIC), against 83.3%, 90.5%, 90.9% or 92.3% of the tested isolates, respectively. Apramycin alone was bactericidal at 24†h against 9.5% and 33.3% of the tested isolates at concentrations equal to 1× and 2× MIC, while the combination of apramycin at 2× MIC with colistin, meropenem or sulbactam was bactericidal against all isolates tested (100%). The apramycin 2× MIC/minocycline combination had bactericidal activity against 90.9% of the tested isolates. CONCLUSIONS: Apramycin combinations may have potential as a treatment option for XDR/pandrug-resistant (PDR) A. baumannii infections and warrant validation in the clinical setting, when this new aminoglycoside is available for clinical use.