[Alteration of bacteria induced by subinhibitory concentrations of cefixime: consequences on bactericidal activity of human polynuclear neutrophils].

Subinhibitory concentrations of most parenteral cephalosporins have been reported to alter bacterial infectivity and, in particular, to increase the susceptibility of altered bacteria to the killing effects of polymorphonuclear neutrophils (PMN). Few data on this issue are available for oral cephalosporins. This study investigated the effects of sub-MIC concentrations of the new oral cephalosporin cefixime on two bacterial targets, i.e., S. aureus 209P (MIC 20 mg/l) and E. coli K12 (MIC 0.15 mg/l). After overnight incubation (18 hours) with 10 or 5 mg/l cefixime, susceptibility of S. aureus to the killing effects of PMNs was increased two-fold as compared with control organisms and susceptibility to the O2-independent PMN bactericidal system (PMN extract) was also increased. In contrast, the susceptibility of E. coli to PMN and to cell-free bactericidal systems was identical for cefixime-exposed strains (0.1 and 0.05 mg/l) and for unexposed controls. However, cefixime-exposed E. coli were filamentous, suggesting that bactericidal efficacy in terms of the bacterial mass eliminated was enhanced in exposed strains. These data show that low levels of cefixime are capable of producing major alterations in susceptible and resistant bacteria and of increasing their susceptibility to PMN. These effects may be relevant in vivo, in particular when low concentrations of antibiotics persist over long periods in infected sites.