Molecular interaction mechanisms of pathogen biofilms and host immune cells

Abstract

Bacteria species such as Pseudomonas aeruginosa and Staphylococcus aureus can commonly be found co-existing along each other in chronic infections as mixedspecies biofilm. Bacteria found within mixed-species biofilms become even more resistant to host immune defences and antimicrobial agents compared to singlespecies biofilms. This study aims to determine whether P. aeruginosa is able to exert protective effects onto S. aureus against macrophage engulfment. This was accomplished by visualising differences in bacteria internalisation within macrophages between P. aeruginosa strains that were unable to form either Type IV pili (ΔpilA), or extracellular polysaccharides which provide structural integrity to biofilms, Pel (ΔpelA) and Psl (ΔpslBCD). The lack of functional Type IV pili did not seem to cause bacteria to be more susceptible to phagocytosis while bacteria lacking either Pel or Psl exopolysaccharides were found to be slightly more vulnerable to being engulfed by macrophages. Structural constituents contributed by P. aeruginosa appeared to have some effect on the overall resistance of the mixedspecies biofilm against host immune functions.