Table 1.
The virulence factors of P. aeruginosa.
| Categories | Virulence factors | Functions | Refs |
|---|---|---|---|
| Bacterial surface structures | |||
| surface appendages | Type IV pili | Attachment to host cells, bacterial twitching and swarming motility, biofilm formation | (Whitchurch et al., 2004; Overhage et al., 2008; Burrows, 2012b) |
| Flagella | Swarming motility, biofilm formation, bacterial adhesion and other pathogenic adaptations | (Sampedro et al., 2015) | |
| Outer membrane component | Lipopolysaccharide | Stimulation of host inflammatory response, resistance to serum killing and phagocytosis | (Pier, 2007) |
| Secretion systems | Type 1 secretion system (T1SS) | Secretion of alkaline proteases, utilization of iron, heme uptake | (Bleves et al., 2010) |
| Type 2 secretion system (T2SS) | Secretion of various lytic enzymes | (Jyot et al., 2011) | |
| Type 3 secretion system (T3SS) | Injection of virulent effectors into host cells | (Cornelis, 2010a; Notti and Stebbins, 2016) | |
| Type 5 secretion system (T5SS) | Secretion of proteins related to biofilm formation and adhesion | (Salacha et al., 2010) (Ma et al., 2020) | |
| Type 6 secretion system (T6SS) | Delivery of toxins to neighboring bacteria, translocation of effectors to host cells, biofilm formation | (Basler et al., 2013; Chen et al., 2015; Gallique et al., 2017) | |
| Secreted factors | |||
| Exopolysaccharide | Alginate | Biofilm formation, Immune evasion, bacterial adhesion, mostly existed in strains isolated from infected patients | (Nivens et al., 2001; Song et al., 2003; Ellis and Kuehn, 2010) |
| Pel and Psl | Biofilm formation, Immune evasion, bacterial adhesion, mostly existed in strains isolated from environment | (Ma et al., 2007; Colvin et al., 2012) | |
| Siderophores | Pyoverdine | Chelating irons, promoting bacteria growth, contributing to bacterial virulence | (Ravel and Cornelis, 2003; Bonneau et al., 2020) (Sass et al., 2020) |
| Pyochelin (Pch) | Chelating irons, promoting bacteria growth, contributing to bacterial virulence | (Poole and McKay, 2003; Roche et al., 2021) (Sass et al., 2020) | |
| Protease | Alkaline protease (AprA) | Regulation of quorum sensing, protection of bacteria from host defense | (Matsumoto et al., 1998; Casilag et al., 2015) |
| Elastase A and B (LasA and LasB) | Degrading proteins in host tissues, causing tissue damage | (Kessler et al., 1998; Mariencheck et al., 2003) | |
| Protease IV | Degrades host proteins that involve in immunity against infection | (Engel et al., 1998; Bradshaw et al., 2018) | |
| Toxin | T3SS effectors (ExoS, ExoT, ExoU and ExoY) | Disruption of host actin cytoskeleton, interference of cell-to-cell junctions, induction of host cell apoptosis | (Yahr et al., 1996; Yahr et al., 1998; Sundin et al., 2001; Sato et al., 2003) |
| Exolysin (ExlA) | Pore-forming on the host cell membrane | (Michalska and Wolf, 2015; Basso et al., 2017) | |
| Exotoxin A (PEA) | Inhibition of protein synthesis resulting in cell death | (Michalska and Wolf, 2015) | |
| Lipase A (LipA) | Immunomodulator, damaging host tissue | (Tielen et al., 2013) | |
| Phospholipase C (PLC) | Degrading the phospholipid surfactant, damaging host cells | (Vasil et al., 1991; Sun et al., 2014) | |
| Lipoxygenase (LoxA) | Interference of the host lipid signaling, regulation of bacterial invasion process | (Morello et al., 2019a) | |
| Leukocidin | Inhibition of host immune functions | (Homma et al., 1984; Bouillot et al., 2020) | |
| Pyocyanin (PCN) | Suppresses immune response, cytotoxic to host cells | (Bianchi et al., 2008) (Hall et al., 2016) | |
| Bacterial cell-to-cell interaction | |||
| Quorum-sensing (QS) | – | Regulation of the production virulence factors, integration of the environmental stress, modulating production of biofilm and swarming and twitching motilities | (Rutherford and Bassler, 2012; Pérez-Pérez et al., 2017; Li et al., 2018; Hemmati et al., 2020) |
| Biofilm | – | Escape from host immune responses, resistance against antibiotics, persistency of bacteria under harsh conditions | (Lewis, 2001; Thi et al., 2020) |