Influence of subinhibitory concentrations of ceftriaxone on opsonization and killing of Pseudomonas aeruginosa by human neutrophils.

Ceftriaxone, a 2-aminothiazolyl cephalosporin does not alter human neutrophil (PMN) bactericidal function. However, low concentrations of ceftriaxone induce some bacterial strains to be more sensitive to PMN killing. We have studied the effect of a subinhibitory concentration of ceftriaxone (10 mg/l) on Pseudomonas aeruginosa (MIC greater than 128 mg/l). After an overnight exposure to this concentration of ceftriaxone, P. aeruginosa elongated into filaments. PMN killing of ceftriaxone-treated bacteria was better than killing of control bacteria. This enhanced killing was correlated with an increased sensitivity to oxygen-dependent bacterial killing. Furthermore, the altered bacteria induced a greater oxidative response of PMN which was independent of their chemiluminescence response after stimulation by control P. aeruginosa. This increased oxidative burst was attributable to both non-opsonodependent stimulation and to increased deposit of opsonins.