Escherichia coli

Question 1

General information about E. coli?

Answer 1

Gram-negative

In the Enterobacteria family:

• reduce nitrates —> nitrites, ferment glucose

In soil, water, on plants, in digestive flora of humans and animals (mostly intestines)

Question 2

Tableaux clinique:

Answer 2

Infections intestinales in developing countries

Infections extra-intestinales in industrialized

Question 3

What is the morphology of E. coli?

Answer 3

gram negative, taille moyenne, bouts arrondis, mobile, non sporulé

Question 4

How is E. coli cultured?

Answer 4

32C-40C

Milieux peu complexes

Milieux sélectifs et différentiels:

• Gélose MacConkey —> sels biliaires et le crystal violet inhibe les Gram +, lactose
• Aérobie, anaérobie facultatif

Question 5

How is the paroi of E. coli structured?

Answer 5

1. Structure rigide
2. LPS (endotoxine) dans le feuillet externe
3. Paroi de peptidoglycans
4. Membrane cellulaire

Question 6

What is the structure of the LPS on E. coli?

Answer 6

Lipid A —> core —> chaînes polysaccharidiques (antigène O)

Question 7

What is lipid A?

Answer 7

Part rich in glucosamine and other part that is toxic and responsible for “choc endotoxine”

Question 8

What is the core?

Answer 8

repeated sequence of polysaccharides, mostly similar in most gram - bacteria

Question 9

What are the chaînes polysaccharidiques?

Answer 9

Ag de surface O, used for identification of strain

Question 10

What are the biological effects of endotoxins?

Answer 10

Toxic for mammals:

• action directe: hémolysine
• action indirecte: recognized by the immune system

small quantities —> fever

large quantities —> hypotension, marginalization of PMNs and platelets (disseminated vascular coagulation)

Question 11

What are entérotoxines?

Answer 11

Diarrhea acquired in the tropics

Plasmid is tranferable

Toxines ST et LT

Question 12

What is toxine ST?

Answer 12

Heat-stable toxin:

• Survives at 100C for up to 30 minutes
• Only works on enterocytes
• Leads to secretion of liquid
• Anti-absorbing action

Question 13

What is toxine LT?

Answer 13

Heat-labile toxine

• Destroyed by 30 mins at 65C
• Similar to cholera toxin
• Causes Cl secretion (water and Na… follow passively)
• Create important liquid and electrolytic loss

Question 14

What is vérotoxine (shiga-toxine)?

Answer 14

Intefere with protein synthesis

Lyse renal and intestinal endothelial cells (#1 cause of insuffisance rénale aiguë in children and can cause ischemia by thrombosis of small vessels)

Question 15

Other toxins: (3 main types)

Answer 15

Hémolysines, hémagglutinines, leucocidines

Question 16

E. coli antigenic profil and nomenclature:

Answer 16

Antigen H: flagella

Antigen O: antigène polysaccharidique

• ex: E. coli O:157 H:7

Question 17

How to UTIs work?

Answer 17

Urine is normally sterile

Principal pathogens: E. coli, K. pneumoniae, Proteus/Entérococcus

Question 18

What is considered a bactériurie significative?

Answer 18

>10^8 bacteria/litre

Question 19

What is considered a bactériurie asymptomatique?

Answer 19

>10^8 bacteria/litre but asymptomatic

Question 20

What is the two different forms of pathogenesis of UTIs?

Answer 20

1. Voie ascendante
2. Voie hématogène

Question 21

How are UTIs treated?

Answer 21

Antibiotics and prophylaxis

Question 22

What is cystitis?

Answer 22

inflammation of the bladder, usually caused by a bladder infection

Signs and symptoms:

• Dysuria, pollakiuria (benign idiopathic urinary frequency), nycturia, mictional urgency, macroscopic hematuria, no systemic sx

Question 23

What is pyelonephritis?

Answer 23

inflammation of the kidney, typically due to a bacterial infection

Signs and symptoms:

• Fever, chills, dysuria, pollakiuria, increase in frequency of urination, urgency, pain in kidney area (flank)

Question 24

What is septicemia?

Answer 24

Serious bloodstream infection:

Question 25

Where can septicemia originate?

Answer 25

1. skin, genitourinary system, respiratory system, digestive system (bile ducts, intestines, etc.) 2. can be acquired in the community 3. maladie nosocomiale (particularly in resistant strains to antibiotics)

Question 26

What is the pathogenicity of septicemia?

Answer 26

Colonization and infection of foreign bodies Bris de peau et des muqueuses Obstruction Abcès

Question 27

How is septicemia dx and tx?

Answer 27

**How is it diagnosed?** Clinic, hemoculture, culture du site d'origine suspecté **How is it treated?** Antibiotics, removal of foreign bodies, draining abscess, treatment of shock to maintain BP

Question 28

What is E. coli meningitis?

Answer 28

Neonatal meningitis after infection to group B strep * Meningitis during cranial trauma or secondary to septicaemia

Question 29

What is an infection entérique causée par E. coli? ( 5 kinds)

Answer 29

1. **ETEC (enterotoxinogen)** 2. **EPEC (enteropathogen)** 3. **EIEC (enteroinvasive)** 4. **EHEC (enterohemorragic)** 5. **EAEC (enteroadherent)** Production of toxins —\> non-inflammatory * Invasion and destruction of the muqueuse * Shigella * E. coli entéroinvasif * Salmonella typhi

Question 30

What is travellers diarrhea?

Answer 30

50% of cases due to E. coli 2 toxins: LT and ST Secretion of water into the luminal surface of the small intestine

Question 31

Signs and sx of traveller's diarrhea:

Answer 31

Incubation: * ETEC: a couple hours - 2 days * Other etiologies: 4-14 days (shigella, Campylobacter, Salmonella) * 1-5 days Abdominal cramping Diarrhea (no bleeding) Absence of systemic signs

Question 32

How is traveller's diarrhea dx and tx?

Answer 32

**Dx:** Clinic, no routine lab testing **Treatment:** Oral rehydration, Lomotil/Imodium, Bismuth Subsalicylate, NO ANTIBIOTICS

Question 33

What are the signs and sx of E. coli entéroinvasif?

Answer 33

Fever and abdominal cramping **Ténesme** (tension douloureuse, dans la région de l'anus ou de la vessie, avec sensation de brûlure et envie constante d'aller à la selle ou d'uriner) Bloody stool 5-7 days

Question 34

How is E. coli entéroinvasif dx?

Answer 34

Dx in clinic Lab: No routine, serogrouping

Question 35

How is E. coli entéroinvasif tx?

Answer 35

Rehydration and antibiotics

Question 36

What is E. coli entérohémorragique?

Answer 36

**Children and old people, due to minced meat, raw milk, contaminated water** **What is it?** * Toxin that inhibits protein synthesis * Bacteriophage * Production of toxins that increase with stress —\> lysis of E. coli cells * Death of cells in muqueuses and endothelial cells * **SHU** (syndrome hémolytique urémique) —\> most frequent cause of ARI in children * **PTT** (purpura thrombocytopénique thrombolytique) —\> ischemia by thrombosis of small vessels

Question 37

What are some signs and sx of E. coli entérohémorragique?

Answer 37

Abdominal pain, aqueous diarrhea —\> hemorragique, no fever, 7-8 days **7-10 days later:** anuria, oligurie, lethargie, convulsions, coma, death 5%

Question 38

How is E. coli entérohémorragique dx and tx?

Answer 38

**Dx:** * Recherche de E. coli O157:H7 (less than 50% of cases) * Recherche de la vérotoxine (détection d'ADN) * Culture doit distinguer de la shigelle qui possède la même toxine **Treatment:** Rehydration, complications (renal and cerebral), **NO ANTIBIOTICS**