122. General characteristics of diseases caused by Escherichia coli.

Question 1

Etiology of E coli?

Answer 1

Etiology:

• E. coli (Enterobacteriaeceae family)
• Gr(-), lactose (+)
• Antigens:
• O: LPS (181), endotoxin, cell wall antigens (NOT a virulence factor)
• K: polysaccharide (60), capsule antigen
• H: protein (53), flagella antigen
• F: protein (30) - F1-F18, F41, frimbra antigens - species specific
• Normal inhabitant of LI, normal flora, vitamin production
• Pathogenicity: mainly saprophyte (gut flora), some are facultative pathogenic strains
• Virulence factors:
• capsule, endotoxin (LPS, same as cell wall antigens, released when the bacteria breakdown),
• adhesins (frimbrae), toxins, invasive ability (normally cannot invade host cells, some strains can),
• ability of survival in blood
• Adhesins (endotoxin): fimbria -
• human (F2, F3 in newborn children),
• calves (F5, F17, F41),
• pigs (F4 -mostly, F6, F18),
• urogenital (F7-16),
• outer membrane protein of bacteria help with attachment,
• attach to the surface of GI epithelia and damage cells
• Intimin: produced by host cells, but initiated by bacteria
• Fibronectine receptors

Question 2

Toxins of E Coli?

Answer 2

Toxins:

• Enterotoxins: produced in gut
• LT: increased cAMP, large molecule, act on AC enzyme of host
• ST: increased cGMP, smaller, dehydration (normally enterocytes absorb water from gut, but damaged from toxins - enterocytes excrete fluid instead = causing diarrhea),
• metabolic acidosis
• Cytotoxins:
• Verotoxins: SLT/VT1/VT2 - inhibition of protein synthesis (endothel damage > edema
• > hemorrhagic, necrosis)
• Cytotoxic necrotic factor (CNF): human strains
• Cytolethal distending toxin (CDT): human strains, urogenital, extra-intestinal
• Alpha-hemolysin: pore-forming toxin
• Invasive ability
• Survival in blood (siderophors): septicemia strain (replicate and spread in blood)
• Genetic variability

Question 3

Pathotypes of E.coli ?

Answer 3

Pathotypes of E. coli- Enteric

• Enterotoxigenic ETEC
• produces enterotoxins, fimbria - causes diarrhea in suckling animals,
• newborn children, travellers,
• purely toxic effect that causes diarrhea (NO inflammation)
• Enteropathogenic EPEC
• adhesion from intimin, damage mainly microvilli (decreased absorption)
• causing dyspepsia of newborns
• Enterohemorrhagic/Verotoxigenic EHEC/VTEC
• bind with intimin,
• produce verotoxins (damage endothelial cells) -
• causing hemorrhagic colitis/diarrhea,
• hemolytic-uremic syndrome, purely toxic
• effect that causes diarrhea (NO inflammation)
• Enteroinvasive EIEC
• more in humans, dysentery-like
• Enteroadhesive-aggregative EAEC
• mild enteritis in humans
• Combined types: EHEC/EAEC Germany 2011 (O:104:H4)

Question 4

Extra-intestinal of Ecoli?

Answer 4

Extra-intestinal

• Urogenital: adhesin (F7-16), toxins (CNF, CDT, alpha-hemolysin)
• Septicemia, meningitis: newborn children, old people, immune compromised
• Colicin-V plasmid, alpha-hemolysin
• Can survive in blood and spread

Question 5

Diseases of animals caused by E coli ?

Answer 5

Diseases of animals caused by E. coli

• Enteric
• Calves: ETEC, VTEC
• Piglets: ETEC, VTEC, EPEC
• Rabbit: EPEC
• Dog, cat: ETEC, VTEC, EPEC
• Septicemic: calves, poultry
• Urinary tract infection, mastitis: cows, sows (MMA)

Question 6

Epidemiology of E coli?

Answer 6

Epidemiology

• Infection: bacteria replicate in gut (fast, 4X within 1 hr)
• Faeces (high amount), feed/water contaminated with feces, egg
• (poultry: germinative - infected eggs > infected chickens, can also survive on eggshells)
• Predisposing factors:
• insufficient hygiene,
• insufficient feeding of pregnant cows/weak calves,
• insufficient colostrum,
• overcrowding,
• environment/stable (low temperature, high humidity),
• nutritional deficiencies

Question 7

Pathogenesis of E Coli?

Answer 7

Pathogenesis:

• Infection PO: asymptomatic presence in the gut + predisposing factors
• Replicate in gut: production of enterotoxins (act in gut - diarrhea),
• verotoxins (more generalized effects - hemorrhages, edema)
• Septicemia: endotoxin effect, spread in blood and affect different organs

Question 8

Diagnosis of Ecoli ?

Answer 8

Diagnosis:

• epidemiology, clinical signs, PM
• Bacteriology:
• Isolation/identification: pure culture (samples from guts, parenchymal organs)
• Identification of serotype (O, K, H, F): certain serotypes produce certain diseases
• Identification of virulence factors:
• adhesins (agglutination, PCR),
• toxins (isolated gut test - inoculate bacteria into the gut, PCR)
• Examination of AB susceptibility

Question 9

Treatment of E coli?

Answer 9

Treatment

• Enteric diseases: AB that acts in the gut, not necessary absorbed
• Per os AB: polymyxins, quinolones, aminoglycosides, broad spectrum beta-lactam (amox, cephalosporines)
• Rehydration: fluid therapy
• Septicemia: parenteral, generally too late when see signs caused by endotoxins released when the bacteria die
• Mastitis: quinolones, aminoglycosides
• AB resistance

Question 10

Prevention of E Coli?

Answer 10

• Prevention

• Predisposing factors: correct feeding of pregnants, good nutrition and management, hygiene!
• Specific prevention
• Colostrum: received in time, quality (10% of their weight, presence of appropriate AB),
• quantity
• Vaccination: mainly in case of neonatal diseases (vaccination in pregnant animals)
• Probiotics (Gr+): Lactobacillus, Enterococcus, Bifidobacterium - colonize the gut, gut flora will shift to Gr+
• Prebiotics: feed additives