Question

The Ability to Adhere to Host Cells and Resist Physical Removal

Pseudomonas aeruginosa, a common cause of serious respiratory infections on people with cystic fibrosis, produces a single polar flagellum, can secrete a polysaccharide slime composed of alginate, and is able to produce both pili and cell wall adhesins.

How could each of these factors contribute to the bacterium's pathogenosis and in what order might they be used?

Answer 1

The two major pili identified for attachment, adhesion and invasion are flagella and type IV pili. The single polar flagellum is made up of flagellin. Type IV pili has pilin polymers which undergo reversible assembly and disassembly allowing the bacteria to move on surfaces in a manner known as twitching motility. They also help in biofilm formation and serve as adhesins for mammalian cells.

Flagellum aids in motility. The ability to move towards the host cell is an essential prerequisite for adhesion and invasion by the bacteria. The single polar flagellum enables the bacteria to reach the respiratory epithelium and adhere to it. Specifically, flagellum allows to bind to heparin sulphate chains of heparin sulphate proteoglycans that allow efficient attachment at the basolateral surface of epithelial cells.

Slime in the form of alginate (an exopolysaccharide) helps to protect the bacteria from harsh or adverse conditions in its surroundings. It also facilitates adhesion of this bacteria to solid surfaces. When attachment to a substratum is identified, the bacteria activates the alginate biosynthetic genes which leads to enhanced alginate production and therefore establishment of a biofilm. When the bacteria feels the need to move to and colonize a new site, it starts releasing the alginate lyase enzyme which allows detachment of bacteria away from surface. When P. aeruginosa infects the lungs, it produces alginate in response to its environment. Lecithin which is a major surfactant produced in the lungs is known to facilitate mucus production by the P. aeruginosa.