Pseudomonas aeruginosa (P. aeruginosa) is an increasingly prevalent pathogen that can infect immunocompromised organisms, for example, those suffering from AIDS, cancer, and severe burns. P. aeruginosa is a Gram-negative bacterium and like most members, it utilizes a type III secretion system (TTSS) injecting toxins into the cytoplasm of host cells, subsequently initiate infection. The regulation of effector molecule injection is a complex mechanism, of which pcrV (Type III secretion protein PcrV) is regarded as a critical component. It is a 32 kDa protein and is essential for cytotoxicity. PcrV is found to function in both intrabacterial and extracellular circumstances, which suggests that maybe plays more than one role in the pseudomonas infectivity. LcrV shares 42% sequence similarity to PcrV in Yersinia, and they two are all protective antigens against the infection with their respective pathogens. Pseudomonas aeruginosa (P. aeruginosa), a Gram-negative bacterium, is an opportunistic human pathogen that causes life-threatening infections in cystic fibrosis individuals and those with a compromised immune system. P. aeruginosa can induce severe diseases, such as pneumonia, and sepsis, and lead to recalcitrant biofilm infections and inflammations caused by flagellin. Psl (Pseudomonas aeruginosa exopolysaccharide), also known as polysaccharide synthesis locus, encodes a critical component, exopolysaccharide (EPS) for the biofilm formation. Meanwhile, it is reported that EPS are important for the microbial biofilm extracellular matrix. By confocal laser scanning microscopy and electron microscopy, researchers found that psl is mainly composed of galactose-rich and mannose-rich EPS. Psl gene cluster has 15 cotranscribed genes (From pslA to pslO) and is vital for initiating and maintaining biofilm architecture by cell-cell and cell-surface interactions.