Effect of ceftriaxone on Pseudomonas aeruginosa and Staphylococcus aureus in broth, serum, and in combination with human polymorphonuclear leukocytes

We investigated the antibacterial activity of ceftriaxone at concentrations of 1/4 X minimum inhibition concentration (MIC), 1 X MIC and 4 X MIC against a serum-resistant Pseudomonas aeruginosa and a serum-resistant STaphylococcus aureus strain in broth, serum, and in combination with leukocytes. Killing effect of ceftriaxone in broth was significantly better than in serum; ceftriaxone improved leukocyte bactericidal activity without serum on P. aeruginosa, but not on S. aureus. The antibacterial activity of ceftriaxone was most effective in combination with leukocytes and serum, achieving a marked bactericidal effect already at subinhibitory ceftriaxone concentrations.