Differences in neutrophil death among beta-lactam antibiotics after in vitro killing of bacteria

Antibiotic therapy is an essential treatment for gram-negative bacterial infections. Antibiotic-induced endotoxin release and subsequent production of inflammatory cytokines reportedly depend on the type of antibiotic action. This study examined the effects of various beta-lactam antibiotics on cell death of human polymorphonuclear neutrophils (PMNs) cocultured with Escherichia coli (E. coli) in vitro. E. coli morphology after antibiotic treatment was determined. PMNs and E. coli were cocultured with antibiotics for 0, 4, or 12 h. Levels of endotoxin and cytokines (TNF-alpha, IL-1beta, and IL-6) in the supernatants were measured. The filtrates of antibiotic-treated E. coli supernatants were cocultured with PMNs for 0, 4, or 12 h. In all experiments, ampicillin (ABPC), cefazolin sodium (CEZ), cefoperazone sodium (CPZ), latamoxef sodium (LMOX), imipenem (IPM), and polymyxin B sulfate (PLB) were used at 30 microg/mL. PMNs were isolated from healthy volunteers. PMN cell death was assessed by flow cytometry and light microscopy. ABPC, CEZ, CPZ, and LMOX, which induce bacterial filament formation with lysis, caused PMN necrosis when cocultured with E. coli. In contrast, IPM, which induces bacterial spheroplast formation with lysis, caused PMN apoptosis. Levels of endotoxin, TNF-alpha and IL-6 in the supernatants with IPM and PLB were significantly lower than in those with other beta-lactam antibiotics. The filtrates of IPM- and PLB-treated E. coli supernatants induced PMN apoptosis, whereas those treated with other beta-lactam antibiotics increased PMN necrosis. Beta-lactam antibiotics have different impacts on the types of PMN cell death after E. coli killing. Underlying mechanisms and the clinical relevance of IPM-induced PMN apoptosis in severe gram-negative infection warrant further investigation.