Shear rate sensitizes bacterial pathogens to H₂O₂ stress

Area of Science:

• Microbiology
• Biophysics
• Cellular Physiology

Background:

• Cells in nature encounter fluid flow, unlike typical batch cultures.
• Batch cultures neglect flow's impact on cell physiology and stress responses.

Purpose of the Study:

• Investigate the combined effects of shear rate and chemical stress on bacterial transcription.
• Determine if microfluidic conditions reveal novel stress response mechanisms.

Main Methods:

• Utilized microfluidics and single-cell imaging for dynamic cell culture.
• Employed mathematical simulations alongside biophysical experiments.
• Measured transcriptional responses in *Pseudomonas aeruginosa*.

Main Results:

• Observed spatial hydrogen peroxide (H₂O₂) gradients generated by cell scavenging in microfluidics.
• Found high shear rates abolish gradients, inducing a transcriptional stress response.
• Identified a "wind-chill" effect where flow sensitizes cells to 100-1,000x lower H₂O₂ concentrations.
• Noted that effective shear and H₂O₂ levels mirror human bloodstream conditions.

Conclusions:

• Flow-driven dynamics are critical for understanding bacterial stress responses.
• The study reconciles discrepancies in H₂O₂ stress levels between experimental and host environments.
• Flow-induced sensitization to chemical stress is relevant for pathogens like *Staphylococcus aureus* in vivo.