Contribution of an arsenal of virulence factors to pathogenesis of Pseudomonas aeruginosa infections

Pseudomonas aeruginosa is an increasingly prevalent opportunistic pathogen that causes a variety of nosocomial infections, life-threatening diseases in immuno-compromised persons and chronic pulmonary infections in cystic fibrosis patients. The organism's virulence depends on an arsenal of cell-associated and extracellular factors determining the pathogenesis of infections as multifactorial. Most P. aeruginosa infections are both invasive and toxinogenic. Many of the extracellular virulence factors (proteases, exotoxin A, pyocyanin, siderophores, hemolysins) required for tissue invasion and dissemination of P. aeruginosa are controlled by quorum sensing (QS) that enable the bacteria to produce these factors in a coordinated, cell-density-dependent manner and overwhelm the host defense mechanisms during acute infection. Sometimes, QS also contributes to biofilm formation and thus participates in pathogenesis of chronic infection. This system is recognized to be a global regulatory network controlling the expression of a large number of virulence genes either directly or indirectly. Two-component sensor kinases such as RetS, LadS and GacS are also controlling the production of virulence factors as well as the switch from acute to chronic infection. The present review describes the known virulence determinants of P. aeruginosa, the stages of infection as well as the importance of QS in the pathogenesis of P. aeruginosa infection.