Effect of Antibiotics on Polymorphonuclear Neutrophil Apoptosis

Study Objective. To evaluate the effects of various antibiotics—direct and indirect as a result of bacterial killing—on polymorphonuclear neutrophil (PMN) apoptosis. Design. In vitro analysis. Setting. Research laboratory. Intervention. Whole blood collected from healthy human subjects was incubated with and without Klebsiella pneumoniae (1.0 × 105 colony‐forming units [cfu]/ml) plus ceftazidime 50 μg/ml, gentamicin, ciprofloxacin, trovafloxacin, tetracycline, doxycycline, erythromycin, azithromycin (each 5 μg/ml), or lipopolysaccharide 10 μg/ml. After staining with fluorescein‐conjugated annexin V, red blood cells were lysed, and the remaining white blood cells were assessed by flow cytometry with gating on PMNs. Measurements and Main Results. In the absence of K. pneumoniae infection, antibiotic exposure directly decreased PMN apoptosis by 17.8% (range −25.0% to −13.9%, p=0.008) compared with untreated cells. In the presence of K. pneumoniae, all antibiotic treatments, even those with poor in vitro activity for the bacterial isolate, decreased PMN apoptosis by 26.2% (range ×38.0% to −17.8%, p>0.001) compared with untreated control cells and by 36.6% compared with untreated (no antibiotic) K. pneumoniae‐stimulated cells (range −46.2% to −28.0%, p>0.001). Conclusions. All tested antibiotics in clinically relevant concentrations resulted in modest yet consistent decreases in PMN apoptosis. The magnitude of this change increased slightly in the presence of K. pneumoniae infection. In vivo studies are needed to determine whether antibiotic‐associated prolongation of PMN survival improves host response to infection.