Atomic force microscopy study on specificity and non-specificity of interaction forces between Enterococcus faecalis...

Area of Science:

• Microbiology
• Biophysics
• Infectious Diseases

Background:

• Enterococcus faecalis is a major cause of hospital-acquired infections, particularly on indwelling medical devices.
• Aggregation substance (Agg) mediates E. faecalis adherence to biomaterials via positive cooperativity, enhancing biofilm formation.

Purpose of the Study:

• To quantify specific and non-specific interaction forces between E. faecalis cells using atomic force microscopy (AFM).
• To investigate the role of aggregation substance (Agg) in mediating these interaction forces and their correlation with positive cooperativity.

Main Methods:

• Atomic force microscopy (AFM) was employed to measure interaction forces between E. faecalis cells with and without Agg.
• Bacteria were immobilized on a substratum and a tip-less cantilever for force measurements.
• Antibodies against Agg were used to differentiate specific from non-specific interaction forces.

Main Results:

• E. faecalis strains expressing Agg exhibited approximately twofold higher interaction forces (-2.6 to -2.3 nN) compared to strains lacking Agg (-1.3 nN).
• Specific interaction forces mediated by Agg were found to be only twofold stronger than non-specific forces (approx. 1.2 nN).
• Absence of strong cell-cell interaction forces correlated with the absence of positive cooperativity in bacterial adhesion.

Conclusions:

• This study provides the first experimental demonstration using AFM to distinguish specific and non-specific force components in E. faecalis cell interactions.
• The findings highlight that while Agg significantly enhances cell adhesion, the specific force contribution is modest compared to non-specific forces.
• Understanding these forces is critical for developing strategies to prevent E. faecalis infections on medical devices.