Surface hydrophilicity promotes bacterial twitching motility

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Surface Science

Background:

• Bacterial twitching motility, powered by type IV pili (T4P), is vital for virulence and is often studied using colony expansion assays.
• The functionality of T4P is critical for many antibiotic-resistant pathogens, making it a target for countermeasures.
• Previous observations noted that twitching motility of *Acinetobacter* species varied with growth media, with MacConkey agar supporting it better than Luria-Bertani (LB) agar.

Purpose of the Study:

• To investigate the role of bile salts in modulating bacterial twitching motility.
• To elucidate the mechanism by which bile salts and other detergents affect T4P-mediated motility.
• To understand how surface properties influence bacterial colonization and infection by critical pathogens.

Main Methods:

• Assessing twitching motility of *Acinetobacter nosocomialis*, *Acinetobacter baumannii*, and *Pseudomonas aeruginosa* on different agar media and surfaces.
• Supplementing Luria-Bertani (LB) agar with bile salts and other detergents to observe effects on twitching.
• Comparing the effects of detergents with antibiotic-induced stress on twitching motility.
• Evaluating twitching motility on surfaces with varying hydrophilicity, including glass and treated polystyrene.

Main Results:

• Bile salts significantly enhanced twitching motility in *A. nosocomialis*, *A. baumannii*, and *P. aeruginosa* when added to LB agar.
• The stimulatory effect of bile salts on twitching was attributed to altering the physicochemical properties of the twitching surface, specifically reducing hydrophilicity, rather than inducing a physiological stress response.
• Unlike detergents, antibiotics like polymyxin B did not enhance twitching motility.
• Bacteria exhibited increased twitching on hydrophilic surfaces (glass, tissue culture-treated polystyrene), and bile salts lost their stimulatory effect on these surfaces.

Conclusions:

• Bile salts and detergents promote bacterial twitching motility by modifying surface hydrophilicity, not through stress responses.
• Hydrophilic surfaces inherently support T4P-mediated twitching, independent of detergent additives.
• Surface properties are critical determinants of T4P functionality, impacting bacterial virulence and colonization on medical implants and host tissues.