title: Sub-minimal inhibitory concentrations of cefmetazole enhance serum bactericidal activity in vitro by amplifying poly-C9 deposition.
abstract: Serum-resistant organisms grown in sub-minimal inhibitory concentrations (subMICs) of antibiotics in vitro may be rendered sensitive to complement-mediated, serum bactericidal activity. We measured 125I-C3 and 125I-C9 deposition on genetically serum resistant Salmonella montevideo SH5770 (SH5770) that was rendered serum sensitive by growth in sub-MICs of cefmetazole (CMZ), a parenteral, second generation, cephamycin-group antibiotic. Three times as much C3 and over six times as much C9 bound to SH5770 grown in one-fourth the MIC of CMZ compared to broth-grown bacteria. SDS-PAGE analysis and autoradiography showed that neither the ratio of C3b:iC3b (approximately 1:2.5) nor the nature of the C3-bacterial bond was changed by growing the organisms in CMZ. Large amounts of complement membrane attack complexes containing poly-C9 were seen only on CMZ-grown SH5770 by SDS-PAGE and autoradiography. Poly-C9 was also detected only on CMZ-grown bacteria by indirect immunofluorescence and ELISA using a murine monoclonal antibody directed against a neoantigen of poly-C9. Bacterial hydrophobicity increased after growth in CMZ, and transmission electron micrographs of CMZ-grown SH5770 showed cell wall disruption and blebbing. These results indicate that growth in subMICs of CMZ increases bacterial hydrophobic domains available for interacting with the membrane attack complex, C5b-9, allowing formation and stable insertion of bactericidal complexes containing poly-C9.
authors.affiliation: Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510.
authors.forename: J E
authors.initials: JE
authors.lastname: Schweinle
authors.forename: M
authors.initials: M
authors.lastname: Nishiyasu
mesh_terms: D001770:Blood Bactericidal Activity / Q000187:drug effects*; D015311:Cefmetazole / Q000494:pharmacology*; D003176:Complement C3 / Q000378:metabolism; D003186:Complement C9 / Q000378:metabolism*; D015938:Complement Membrane Attack Complex / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques
chemical_list: D003176:Complement C3; D003186:Complement C9; D015938:Complement Membrane Attack Complex; C040352:complement C9 polymer; D015311:Cefmetazole