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Published on: June 23, 2022
Investigation of the Inoculum Effect of Antimicrobial Peptides Utilizing a Microfluidic Chip Platform
Haohua Mei1,2, Weihong Yin2, Zheyu Zou3
1College of Life Sciences, Zhejiang University, Hangzhou310027, P. R. China.
Abstract:
In infections with high bacterial loads, such as peritonitis, antibiotic efficacy is often compromised by the inoculum effect. Antimicrobial peptides, despite their broad-spectrum activity, are similarly affected. To elucidate the mechanisms underlying the inoculum effect of antimicrobial peptides, this study employed microfluidic chips to isolate and analyze single bacterial cells. Comparison of population-level minimum inhibitory concentration obtained from 96-well assays with single-cell minimum inhibitory concentration revealed that minimum inhibitory concentration increased with inoculum density, whereas single-cell minimum inhibitory concentration remained unchanged. Further investigation revealed that intracellular components released from lysed cells and OmpT-mediated peptide degradation substantially elevated population resistance, effects that were absent under single-cell isolation. These results demonstrate that the inoculum effect of antimicrobial peptides stems from population-dependent interactions, intracellular material release, and enzymatic degradation rather than intrinsic single-cell resistance. This work provides mechanistic insight into the inoculum effect of antimicrobial peptides and informs the optimization of their clinical application.
Insights
The inoculum effect impacting antimicrobial peptides is not due to single-cell resistance. Population-dependent interactions, like cell lysis and peptide degradation, cause this phenomenon.
Area of Science:
- Microbiology
- Biochemistry
- Drug Discovery
Background:
- The inoculum effect compromises antibiotic efficacy in high bacterial load infections.
- Antimicrobial peptides (AMPs) exhibit broad-spectrum activity but are also susceptible to the inoculum effect.
Purpose of the Study:
- To investigate the mechanisms behind the inoculum effect of antimicrobial peptides.
- To differentiate between population-level and single-cell resistance to AMPs.
Main Methods:
- Utilized microfluidic chips for single bacterial cell isolation and analysis.
- Compared population-level minimum inhibitory concentration (MIC) from 96-well assays with single-cell MIC.
- Investigated the role of intracellular components and OmpT-mediated degradation.
Main Results:
- Population-level MIC increased with inoculum density; single-cell MIC remained constant.
- Intracellular components from lysed cells and OmpT-mediated degradation increased population resistance.
- These population-dependent resistance factors were absent in single-cell analyses.
Conclusions:
- The inoculum effect of AMPs arises from population-dependent interactions, not intrinsic single-cell resistance.
- Mechanisms include release of intracellular material and enzymatic degradation of peptides.
- Findings provide insights for optimizing AMP clinical applications.
