Table 5. The characteristics and functions of each functional category that was more inclined to be found in common VFs.

Functional categories	Characteristics	Functions	References
Flagella	Surface organelle	Flagella are used for motility and chemotaxis in bacteria	61
Capsule	Primarily structural component of gram-positive cell wall	Protect and avoid phagocytosis	62
Lipopolysaccharide (LPS) or endotoxin	Components of the outer membrane of the cell wall of gram-negative bacteria	Activate the host complement pathway	63
Iron uptake	Mediate the release of host iron for parasitic consumption	Used for iron uptake and heme-utilization	64
Regulation	Regulate the expression of various genes	Adapt to the host surrounding	3 and 53
Type VI secretion system	T6SSs are widespread in gram-negative proteobacteria	A secretory system that play a general role in mediating host interaction	65
Type II secretion system	T2SSs are encoded by genes of the general secretion pathway (gsp) and are widely distributed in gram-negative bacteria	Main terminal branch of the general secretory pathway	66