BAY-Y 3118 is potent against Haemophilhs influenzae, Moraxela catarrhalis, Acinetobacter baumannii, Xanthomonas maltophiia, gram-positive cocci , and anaerobes; MICs for 50%o of the strains (MIC ₅₀ s) and MIC ₉₀ s are ≤0.015 and ≤0.015, ≤0.015 and ≤0.015, 0.03 and 2, 0.25 and 0.5, 0.06 and 1, and 0.12 and 0.25 μg/mL, respectively. The cellular concentration-to-extracellular concentration ratio of BAY-Y 3118 is higher than 6.3 at extracellular concentrations ranging from 2 to 100 mg/L. The uptake of BAY-Y 3118 is rapid, reversible and nonsaturable. The intracellular penetration of BAY-Y 3118 is significantly affected by environmental temperature and cell viability. BAY-Y 3118 reaches high intracellular concentrations within human polymorphonuclear leukocytes (PMNs) and remains active intracellularly. All strains of L. monocytogenes and other Listeria spp. are highly susceptible; the MICs for these organisms ranges from 0.062 to 0.25 μg/mL. BAY-Y 3118 is rapidly bactericidal in vitro , with a postantibiotic effect occurring for 3 h after removal of the antibiotic. L. monocytogenes is eliminated from infected L929 cells treated with BAY-Y 3118, suggesting a bactericidal effect on the listeriae in these cells.

Immunocompetent mice are rapidly cured by treatment with 4 mg every 12 h. Concomitantly, the levels of interleukin 6 and gamma interferon in mouse sera decline rapidly. In immunocompetent mice, treatment with 2 mg of BAY-Y 3118 every 12 h results in a greater initial reduction in the listerial counts in the organs than treatment with 2 mg of ampicillin every 12 h. BAY-Y 3118 completely eliminates L. monocytogenes from the livers and spleens of chronically infected nude mice.