Use of Alternative Gelling Agents Reveals the Role of Rhamnolipids in Pseudomonas aeruginosa Surface Motility.

Pseudomonas aeruginosa is a motile bacterium able to exhibit a social surface behaviour known as swarming motility. Swarming requires the polar flagellum of P. aeruginosa as well as the secretion of wetting agents to ease the spread across the surface. However, our knowledge on swarming is limited to observed phenotypes on agar-solidified media. To study the surface behaviour and the impact of wetting agents of P. aeruginosa on other surfaces, we assessed surface motility capabilities of the prototypical strain PA14 on semi-solid media solidified with alternative gelling agents, gellan gum and carrageenan. We found that, on these alternative surfaces, the characteristic dendritic spreading pattern of P. aeruginosa is drastically altered. One striking feature is the loss of dependence on rhamnolipids to spread effectively on plates solidified with these alternative gelling agents. Indeed, a rhlA-null mutant unable to produce its wetting agents still spreads effectively, albeit in a circular shape on both the gellan gum- and carrageenan-based media. Our data indicate that rhamnolipids do not have such a crucial role in achieving surface colonization of non-agar plates, suggesting a strong dependence on the physical properties of the tested surface. The use of alternative gelling agent provides new means to reveal unknown features of bacterial surface behaviour.

An Organ System-Based Synopsis of Pseudomonas aeruginosa Virulence.

Driven in part by its metabolic versatility, high intrinsic antibiotic resistance, and a large repertoire of virulence factors, Pseudomonas aeruginosa is expertly adapted to thrive in a wide variety of environments, and in the process, making it a notorious opportunistic pathogen. Apart from the extensively studied chronic infection in the lungs of people with cystic fibrosis (CF), P. aeruginosa also causes multiple serious infections encompassing essentially all organs of the human body, among others, lung infection in patients with chronic obstructive pulmonary disease, primary ciliary dyskinesia and ventilator-associated pneumonia; bacteremia and sepsis; soft tissue infection in burns, open wounds and postsurgery patients; urinary tract infection; diabetic foot ulcers; chronic suppurative otitis media and otitis externa; and keratitis associated with extended contact lens use. Although well characterized in the context of CF, pathogenic processes mediated by various P. aeruginosa virulence factors in other organ systems remain poorly understood. In this review, we use an organ system-based approach to provide a synopsis of disease mechanisms exerted by P. aeruginosa virulence determinants that contribute to its success as a versatile pathogen.