Effects of antibiotic class on the macrophage inflammatory response to Streptococcus pneumoniae

Area of Science:

• Immunology
• Microbiology
• Pharmacology

Background:

• Antibiotic selection influences host inflammatory responses during invasive bacterial infections.
• Prior research on Gram-negative bacteria suggests antibiotic-mediated release of cell wall components exacerbates inflammation.
• The impact of antibiotic mechanisms on Gram-positive organisms' inflammatory effects remains less understood.

Purpose of the Study:

• To investigate the hypothesis that Streptococcus pneumoniae elicits greater macrophage inflammatory mediator production when targeted by cell wall active antibiotics compared to protein synthesis inhibitors.
• To elucidate the role of the antimicrobial mechanism of action in modulating host immune responses to Gram-positive bacterial stimulation.

Main Methods:

• RAW 264.7 murine macrophages were stimulated with Streptococcus pneumoniae in the presence of either oxacillin (cell wall active) or clindamycin (protein synthesis inhibitor).
• Accumulation of inducible nitric oxide synthase (iNOS) and tumor necrosis factor (TNF) was measured.
• Experiments included controls for antibiotic effects on macrophages alone, with lipopolysaccharide, and assessed for endotoxin contamination using polymyxin B.

Main Results:

• Stimulation with Streptococcus pneumoniae and oxacillin resulted in significantly higher levels of iNOS and TNF compared to stimulation with Streptococcus pneumoniae and clindamycin.
• Neither oxacillin nor clindamycin alone or with lipopolysaccharide directly altered macrophage immune response.
• Polymyxin B preincubation confirmed that endotoxin contamination did not confound the observed iNOS or TNF levels.

Conclusions:

• The mechanism of action of antibiotics significantly influences macrophage inflammatory mediator production following Streptococcus pneumoniae stimulation.
• Cell wall active antibiotics, exemplified by oxacillin, induce a more pronounced inflammatory response from macrophages compared to protein synthesis inhibitors like clindamycin when acting on Streptococcus pneumoniae.