In vitro activity of a polyhexanide–betaine solution against high-risk clones of multidrug-resistant nosocomial pathogens

To determine the in vitro activity of a polyhexanide–betaine solution against collection strains and multidrug-resistant (MDR) nosocomial isolates, including high-risk clones.We studied of 8 ATCC and 21 MDR clinical strains of Staphylococcus aureus, Enterococcus faecium, Enterococcus faecalis, Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa, including the multiresistant high-risk clones. The MICs and MBCs of a 0.1% polyhexanide–0.1% betaine solution were determined by microdilution. For each species, strains with the highest MICs were selected for further experiments.The dilution–neutralization test (PrEN 12054) was performed by incubating bacterial inocula of 106CFU/mL for 1min with undiluted 0.1% polyhexanide–betaine solution. The CFUs were counted after neutralization.Growth curves and time-kill curves at concentrations of 0.25, 1, 4, and 8×MIC, were performed. MICs of recovered strains were determined when regrowth was observed in time-kill studies after 24h of incubation.Strains with reduced susceptibility were selected by serial passage on plates with increasing concentrations of polyhexanide–betaine, and MICs were determined.Polyhexanide–betaine MIC range was 0.5–8mg/L. MBCs equalled or were 1 dilution higher than MICs. The dilution–neutralization method showed total inoculum clearance of all strains. In time-kill curves, no regrowth was observed at 4×MIC, except for S. aureus (8×MIC). Increased MICs were not observed in time-kill curves, or after serial passages after exposure to polyhexanide–betaine.Polyhexanide–betaine presented bactericidal activity against all MDR clinical isolates tested, including high-risk clones, at significantly lower concentrations and time of activity than those commercially used.