| Virulence factor | Main components | Major function(s) |
| Capsule (77 K serotypes) | K1 or K2 capsular polysaccharide | Antiphagocytosis |
| Hypermucoviscosity phenotype | Extracapsular polysaccharide | Serum resistance |
| Lipopolysaccharide (O-antigen 9 serotypes: O1, O2, O2ac, O3, O4, O5, O7, O8, and O12) | Lipopolysaccharide | Endotoxin |
| O side chain | Serum resistance | |
| Siderophores | Enterobactin, aerobactin, aerobactin receptor, kfu iron uptake system | Enhanced growth |
| Pili (fimbriae) | Adhesin | Attachment |
| Type 1 pili (FimH adhesion) | Mannose-sensitive | |
| Type 3 pili (MrkD adhesion) | Mannose-resistant |
