Fosfomycin enhanced the killing of tobramycin against P. aeruginosa ATCC 27853 (a) and S. aureus ATCC 29213 (b), relative to the component weights of fosfomycin and tobramycin. The fosfomycin enantiomer CY-230 and tobramycin combination did not demonstrate enhanced killing relative to its components against P. aeruginosa (c). Time-kill curves were conducted in CAMHB supplemented with 2 g/liter of PGM. Antibiotics were tested at the following concentrations: fosfomycin, 12.8 μg/ml, plus tobramycin, 3.2 μg/ml (open squares); fosfomycin, 12.8 μg/ml (closed circles); tobramycin, 3.2 μg/ml (closed triangles); fosfomycin enantiomer Cy-230, 12.8 μg/ml, plus tobramycin, 3.2 μg/ml (open triangles); and cy-230, 12.8 μg/ml (open circles). Closed squares, no drug; dotted line, bactericidal killing.