Cefdinir-induced modification of the susceptibility of bacteria to the antibacterial activity of human serum and polymorphonuclear neutrophils

The effect of serum on the bactericidal activity of cefdinir, and the ability of the antibiotic to modify the interaction of bacteria with human polymorphonuclear neutrophils were assessed. In the presence of antibiotic, serum-resistant Escherichia coli were sensitised to the bactericidal activity of normal human serum. Cefdinir enhanced opsonophagocytic killing of Escherichia coli and Staphylococcus aureus at suprainhibitory concentrations. Significant potentiation of killing occurred with the combination of inhibitory concentrations of cefdinir, neutrophils and sub-optimal levels of serum opsonins. Pre-exposure of Escherichia coli, but not Staphylococcus aureus, to cefdinir enhanced phagocytic uptake and killing of the antibiotic-damaged bacteria. These results indicate that cefdinir-mediated phenotypic modification of Escherichia coli renders the bacteria susceptible to serum antibacterial activity and phagocytic uptake and intracellular killing.