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Metabolic Profiling to Determine Bactericidal or Bacteriostatic Effects of New Natural Products using Isothermal Microcalorimetry
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Metabolic Profiling to Determine Bactericidal or Bacteriostatic Effects of New Natural Products using Isothermal Microcalorimetry

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Sub-minimal inhibitory concentrations of cefmetazole enhance serum bactericidal activity in vitro by amplifying

J E Schweinle1, M Nishiyasu

  • 1Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510.

The Journal of Clinical Investigation
|April 1, 1992
PubMed

Insights

Growth in sub-minimal inhibitory concentrations of cefmetazole (CMZ) renders serum-resistant bacteria sensitive to complement-mediated killing. This occurs due to increased bacterial hydrophobicity and enhanced formation of bactericidal membrane attack complexes containing poly-C9.

Area of Science:

  • Microbiology
  • Immunology
  • Bacteriology

Background:

  • Serum resistance is a key virulence factor for many bacterial pathogens.
  • Complement-mediated bactericidal activity is a crucial component of innate immunity.
  • Sub-minimal inhibitory concentrations (subMICs) of antibiotics can alter bacterial physiology.

Purpose of the Study:

  • To investigate if subMIC cefmetazole (CMZ) treatment can restore serum sensitivity to serum-resistant bacteria.
  • To elucidate the mechanisms by which CMZ affects bacterial susceptibility to complement.

Main Methods:

  • Growth of Salmonella montevideo SH5770 in subMIC cefmetazole (CMZ).
  • Measurement of 125I-C3 and 125I-C9 deposition on bacteria.
  • SDS-PAGE, autoradiography, indirect immunofluorescence, and ELISA for complement component analysis.
  • Assessment of bacterial hydrophobicity and cell wall integrity via electron microscopy.

Main Results:

  • CMZ-treated bacteria showed significantly increased deposition of C3 and C9 compared to untreated bacteria.
  • SDS-PAGE confirmed enhanced formation of complement membrane attack complexes (poly-C9) on CMZ-grown bacteria.
  • Bacterial hydrophobicity increased, and cell wall disruption/blebbing was observed after CMZ treatment.
  • The ratio of C3b:iC3b and the nature of the C3-bacterial bond remained unchanged.

Conclusions:

  • Growth in subMIC cefmetazole (CMZ) effectively renders serum-resistant Salmonella sensitive to complement-mediated killing.
  • CMZ treatment enhances bacterial susceptibility by increasing cell surface hydrophobicity, facilitating membrane attack complex (C5b-9) formation and stable insertion of poly-C9.
  • This study highlights a novel mechanism by which sub-antibiotic concentrations can modulate bacterial-host immune interactions.

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