Neutrophil Extracellular Mitochondria Are Endowed With Direct Bacteriostatic/Bactericidal Activity on Staphylococcus...

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Neutrophils are key immune cells that combat infections using various mechanisms.
• Extracellular mitochondria released by neutrophils can tag bacteria for enhanced phagocytosis.
• Mitochondria, originating from bacteria, may possess intrinsic antimicrobial properties.

Purpose of the Study:

• To investigate the direct bacteriostatic and bactericidal potential of extracellular mitochondria.
• To determine the effect of neutrophils' mitochondria on Staphylococcus aureus growth and viability.
• To explore the role of mitochondrial reactive oxygen species (mROS) in this antimicrobial activity.

Main Methods:

• Isolated neutrophils' mitochondria and co-cultured them with Staphylococcus aureus.
• Assessed bacterial growth using Colony Forming Units (CFU) and optical density.
• Utilized LIVE/DEAD assays and electron microscopy to analyze bacterial viability and mitochondria-bacteria interactions.
• Tested the effect of a mitochondrial reactive oxygen species (mROS) inhibitor, MitoQ.

Main Results:

• Extracellular mitochondria significantly reduced bacterial growth but did not kill most bacteria.
• Most Staphylococcus aureus cultures exhibited a viable but non-culturable (VBNC) state.
• Electron microscopy revealed morphological changes in bacteria and mitochondria, including cell wall disruption in some bacteria.
• MitoQ partially reversed the growth inhibition, suggesting mROS involvement, but did not affect bacterial viability or interaction.

Conclusions:

• Cell-free extracellular mitochondria exhibit direct bacteriostatic and some bactericidal activity against Staphylococcus aureus.
• This antimicrobial effect is partly mediated by mitochondrial reactive oxygen species (mROS).
• Extracellular mitochondria can induce a VBNC state in bacteria, impacting bacterial survival strategies.