Interaction between human polymorphonuclear leucocytes and bacteria released from in-vitro bacterial biofilm models

Area of Science:

• Microbiology
• Immunology
• Biomaterials

Background:

• Biofilms present challenges in understanding bacterial interactions with host immune cells.
• Existing in vitro models may not fully replicate the complex environment of in vivo biofilms.
• Escherichia coli biofilms are significant in various infections.

Purpose of the Study:

• To compare phagocytic cell interactions with Escherichia coli from a standard in vitro biofilm model and a novel in vivo-like biofilm model.
• To evaluate the resistance of bacteria from these models to phagocytosis and hydrogen peroxide killing.
• To characterize surface differences of bacteria from the two biofilm models.

Main Methods:

• Development of a novel in vitro biofilm model using rat carboxymethylcellulose pouch exudate and cotton threads.
• Culturing Escherichia coli on cotton threads in artificial medium and the novel exudate medium.
• Comparing interactions between phagocytic cells (polymorphonuclear leucocytes) and released bacteria.
• Assessing bacterial resistance to phagocytosis and hydrogen peroxide (H2O2).
• Utilizing electron microscopy with ruthenium red staining to analyze bacterial surface products.

Main Results:

• Bacteria from both the artificial medium biofilm and the novel in vivo-like biofilm exhibited similar resistance to phagocytic cell killing.
• No significant difference in phagocytosis sensitivity was observed compared to standard grown bacteria.
• Bacteria from both biofilm models demonstrated reduced sensitivity to hydrogen peroxide killing.
• Electron microscopy revealed differences in the quantity of surface products interacting with ruthenium red between the two bacterial groups.

Conclusions:

• The novel in vitro biofilm model closely mimics in vivo conditions in terms of bacterial structure and interaction with immune cells.
• Escherichia coli derived from both artificial and in vivo-like biofilms display comparable resistance to phagocytosis and H2O2, suggesting biofilm matrix or surface modifications confer protection.
• Further investigation into the differing surface products may elucidate mechanisms of enhanced bacterial resilience in biofilms.