Table 1.

Virulence factors produced by Enterobacterales.

Virulence Factor Category	Virulence Factor	Role(s) in Virulence	Genes	Organisms	Refrences
Adhesin	Type 1 Fimbriae	Adhesion, colonisation, invasion	fim gene family fim A-I	E. coli	[20,21]
	Type 3 Fimbriae	Adhesion, colonisation	mrkABCDF operon	E. coli, Klebsiella pneumoniae	[22,23]
	F1C Fimbriae	Adhesion, colonisation	focA, focC, focD, focf, focG, focH, focI	E. coli	[24]
	S Fimbriae	Adhesion, colonisation	sfaA-H, sfaS, sfaX, sfaY	E. coli	[25]
	P Fimbriae	Adhesion, colonisation	papA-K	E. coli, P. mirabilis	[26]
	Auf Fimbriae	Adhesion, colonisation	aufA-G	E. coli	[25]
	F9 Fimbriae	Adhesion, colonisation	c1931-c1936	E. coli	[25]
	Stf fimbriae	Adhesion, colonisation	stf	Salmonella spp.	[27]
	Saf fimbriae	Adhesion, colonisation	saf	Salmonella spp.	[27]
	Dr	Adhesion, colonisation	draA-draE, draP	E. coli	[28]
	Afa	Adhesion, colonisation	afaI-afaIV, nfaI, drII	E. coli	[29]
	Curli amyloid fibers	Components of the biofilm extracellular matrix, surface colonisation	csgBA and csgDEFG operons	E. coli, Salmonella spp.	[30]
Autotransporter protein	Temperature-sensitive hemagglutinin	Autotransporter protein	tsh	E. coli	[31]
	SPATE (serine protease autotransporters of Enterobactericeae)	Diverse function s (adhesin, protease, esterase, lipase, etc.)	sat, pic	E. coli, Shigella, Salmonella	[32]
Secretion system	T1SS	Toxin secretion	T1SS operon	E. coli	[33]
	T3SS	Injects effector proteins into the host cells	T3SS genes	E. coli EPEC, E. coli EHEC, Salmonella spp., Shigella	[34]
	T5SS	Autotransporters	T5SS genes	E. coli	[35]
	T6SS	Secretion of antibacterial proteins and many others	sci-1 and sci-2 clusters	E. coli	[36,37]
Toxins	Lipid A	Endotoxin		Salmonella spp., E. coli	[38]
	Alpha-hemolysin (HlyA)	Cytotoxic agent	hlyCABD operon	E. coli, Staphylococcus aureus	[39]
	Colibactin (Clb)	Genotoxic molecule	clb gene cluster	E. coli	[40]
	Colicin	Antimicrobial proteins	Colicin operons	E. coli, Enterobacter cloacae	[41]
	Cytolethal distending toxin (CDT-I to CDT-V)	Cytotoxic agent, block eukaryotic cell cycle	cdt operon	E. coli, Shigella dysenteriae, Salmonella enterica, Campylobacter spp., Aggregatibacter actinomycetemcomitans, Escherichia albertii, Haemophilus ducreyi, Helicobacter spp., Providencia alcalifaciens,	[42]
	Cytotoxic necrotizing factor 1 (CNF-1)	Inflammation and tissue damage	cnf1	E. coli UPEC	[43]
	Hemolysin (HlyF)	Induces autophagy in eukaryotic cells	hlyF	E. coli	[44]
Lipopolysaccharide and capsule	Capsular polysaccharides (K antigen)	Adherence, resistance to host immune system	K-antigen cluster	E. coli, Acinetobacter baumannii, Burkholderia pseudomallei, Vibrio spp.	[45,46,47]
	O-antigen	Adherence and help to overcome host defense mechanisms	O-antigen cluster	E. coli, Salmonella enterica	[48]
Iron acquisition	Siderophores (Enterobactin, Bacillibactin)	Iron acquisition	Siderophore biosynthesis genes	E. coli, K. pneumoniae	[49]
Antimicrobial resistance	Beta-lactamase	Resistance to beta-lactam antibiotics	blaTEM, blaCTX–M, ampC	E. coli, Klebsiella spp.	[50,51]
	Aminoglycoside resistance	Resistance to aminoglycoside antibiotics	Genes encoding aminoglycoside-modifying enzymes (AGMEs)	E. coli, Klebsiella spp.	[52]
	Fluoroquinolones	Resistance to fluoroquinolone antibiotics	qnr genes	E. coli, Klebsiella spp., and other Entorobacterales members	[53]
Plasmids	pO157	Helps with the adherence of bacterial cells to epithelial cells of the intestine	ehxA, etpC to etpO, espp., katP, toxB, ecf, stcE etc.	EHEC O157:H7	[54]
	pB171	Contribute to adherence to epithelial cells of the intestine	parABC locus, etc.	EPEC	[55,56]
	pINV	Essential for invasiveness	ipa–mxi–spa locus etc.	E. coli EIEC, Shigella spp.	[57,58]
	pCoo	Toxins and colonisation factors	cooB, A, C, D, etc.	ETEC	[59]
	pAA	Toxins and fimbriae	Pet, pic, senB, orf3, orf4, aar, capU, virK, shf, etc.	EAEC	[60]
	pYV	Encodes a type III secretion system required for plasmid-borne anti-host factors delivery called Yops	ysc, lcr, yop, etc.	Yersinia enterocolitica and Yersinia pseudotuberculosis	[61]
Flagella	Flagella	Early biofilm formation, adherence, and invasion	flhDC operon	E. coli, S. enterica, Salmonella and other Entorobacterales members	[62,63]
Biofilm	Biofilm	Increases the survival of the bacterial population and enhances the pathogenic ability of the microorganism	fimAICDFGH operon quorum sensing genes, e.g., lusS and pfs, etc.	E. coli, S. enterica, Salmonella, and other Entorobacterales members	[64,65]