Propidium Monoazide is Unreliable for Quantitative Live-Dead Molecular Assays

Area of Science:

• Microbiology
• Molecular Biology
• Biotechnology

Background:

• Propidium monoazide (PMA) is a viability dye used in molecular assays like Polymerase Chain Reaction (PCR).
• PMA distinguishes live from dead cells by cross-linking to DNA in cells with compromised membranes or extracellular DNA upon photoactivation.
• Current applications include pathogen detection and microbiome analysis using 16S rRNA gene sequencing, aiming to reduce bias.

Purpose of the Study:

• To evaluate the effectiveness and reliability of PMA viability assays under varying sample conditions.
• To determine accurate PMA cross-linkage and activity in complex bacterial mixtures.
• To identify limitations and appropriate use cases for PMA in microbial viability studies.

Main Methods:

• Utilized a sensitive quantitative Polymerase Chain Reaction (qPCR) assay.
• Employed post-treatment sample concentration to assess PMA cross-linkage and activity.
• Tested PMA performance across samples with varying concentrations and compositions of bacterial mixtures.

Main Results:

• PMA performance was inconsistent when bacterial concentration and composition were unknown.
• The dye's effectiveness was significantly impacted by the variability in sample matrices.
• Accurate assessment of PMA cross-linkage and activity required controlled sample conditions.

Conclusions:

• Propidium monoazide (PMA) is unreliable for quantitative viability assays when sample composition is unknown.
• PMA is best suited for qualitative viability assessment in samples with a known quantity of dead microbes or extracellular DNA.
• Further optimization or alternative methods may be needed for reliable viability assessment in complex, uncharacterized microbial communities.