Med Bac - Escherichia

Who originally discovered E. coli?

Theodore von Escherich

What did Theodore von Escherich originally call E. coli?

Bacterium coli

(T/F) E. coli is a constant inhabitant of the colon

True

(T/F) Escherichia contains 5 species, but only E. coli is pathogenic to humans.

True

(T/F) E. coli is gram negative, facultative anaerobic, and generally motile.

True

The outer leaflet of the outer membrane of E. coli contains what?

Lipopolysaccharide (LPS)

What are the 3 parts of LPS?

Lipid A, Core Sugars, and O antigen

(T/F) LPS is immunogenic and can cause septic shock (endotoxemia).

True

What type of general infections can E. coli cause?

GIT gastroenteritis, UTI, sepsis

(T/F) E. coli has 3 main reservoirs: humans, animals, and the environment.

True

(T/F) E. coli asymptomatically colonizes the GIT.

True

(T/F) Many pathogenic E. coli strains are zoonotic.

True

What type of entry is E. coli?

Ingress

Zoonotic E. coli transmission to humans is usually through what?

Tainted foods like animal and vegetable products

What is the main disease E. coli can cause in calves?

White scours

What are the other 2 names for white scour disease in calves?

Calf-enteritis and bovine colibacillosis

What are 2 other diseases E. coli can cause in animals?

Bowel oedema and coliform mastitis

Endotoxemia (septic shock) is an exaggerated immune response to specifically what part of LPS?

Lipid A

What host receptor binds to lipid A of LPS?

TLR4

What are the 3 pathovars of diarrheagenic E. coli (DEC)?

ETEC (Enterotoxigenic), EHEC (Enterohemorrhagic), EIEC (Enteroinvasive)

What is the common name for ETEC (enterotoxigenic E. coli)?

Travelers Diarrhea

What is the common name for EHEC (Enterohemorrhagic E. coli)?

Hemorrhagic colitis

What is the common name for EIEC (enteroinvasive E. coli)?

Dysentry

What gene island confers acid resistance to E. coli that allows it to survive the low pH of the stomach?

AFI (acid fitness island)

What gene from the AFI (acid fitness island) confer acid resistance to E. coli?

GAD (Glutamic acid decarboxylase)

Mutation of what GAD gene leads to acid susceptibility in E. coli?

gadE

(T/F) Pathogens with AR (acid resistance) mechanisms have a low infectious dose (ID50).

True

What are the 2 main genes in the GAD AR system?

GadA = Glutamate decarboxylase | GadC = Glutamate antiporter

Describe the acid resistance (AR) mechanism conferred by GadA and GadC.

Physiologic glutamate is transported through GadC and decarboxylated and protonated by GadA to yield GABA → GABA is then exchanged for more glutamate. This proton-scavenging mechanism raises internal pH to 4-5.

Attachment and colonization of EHEC to the intestine (colon) leads to the formation of what?

AE Lesions (attaching and effacing) i.e. pedestals

What pathogenicity island encodes for genes involved in EHEC attachment?

LEE (locus of enterocyte effacement)

How many operons make up LEE?

5 operons

(T/F) Removal of LEE leads to attenuation.

True

What system is encoded on LEE that allows injection of VF into host cells?

Type 3 secretion system (T3SS)

What LEE encoded adherence factor and intestinal receptor is required for EHEC attachment?

Intimin (adherence factor) and Tir (receptor)

Where is intimin located?

On the surface of E. coli

How does intimin bind to Tir?

Tir is secreted into host cells by the LEE encoded T3SS

What protein causes the hallmark pedestals of EHEC attachment?

Tir

How does Tir cause pedestals?

Actin condensation beneath EHEC

What 2 host proteins does Tir recruit that causes actin condensation beneath EHEC?

N-WASP and Arp2/3

AE pedestal lesions permeabilize the intestine and lead to colitis → the attached EHEC then secrete what toxin?

Shiga toxin (STX)

What does shiga toxin (STX) target?

Intestinal blood vessels (and kidneys)

What are the 2 subunits and their purpose in the shiga toxin (STX)?

Subunit A (toxin) and subunit B (receptor)

What does the B subunit of the shiga toxin bind to?

Gb3 in vascular tissue

What is the A subunit of Shiga toxin?

28S rRNA glycosidase

What does subunit A of STX do?

It deadenylates 28S rRNAs → blocks binding of EF-G and EF-Tu to ribosomes, halting protein synthesis

How does the B subunit of Shiga toxin gain entry into the host cell?

Receptor-mediated endocytosis

What symptoms are used for presumptive diagnosis of EHEC hemorrhagic colitis?

Abdominal tenderness, bloody diarrhea, dehydration, low grade fever, hypotension

What two culture plates are used for definitive diagnosis of E. coli?

MacConkey agar and Sorbitol MacConkey (SMAC)

(T/F) MacConkey agar is a selective and differential media for E. coli

True

E. coli can ferment lactose, and appears as what on MacConkey agar?

Pink

Bacteria that cannot ferment lactose on MacConkey agar (ex. Salmonella) appear as what?

Orange

SMAC is a differential media that tests for what?

Sorbitol fermentation

Can EHEC ferment sorbitol?

No

How does EHEC appear on SMAC?

Transparent orange

E. coli that can ferment sorbitol appear as what on SMAC?

Red

(T/F) There are no current licensed vaccines for humans against EHEC.

True

What vaccine is used for EHEC for cattle?

Siderophore receptor and porin (E. coli SRP)

(T/F) Most E. coli gastroenteritis infections are self-limiting and do not require intervention.

True

What standard at home remedies should people do for E. coli gastroenteritis?

Rehydration, rest, and electrolyte replacement

In complicated E. coli infections, what antibiotics are used?

Doxycycline and Trimethoprim (TMP)

In speculation of EHEC HUS (hemolytic uremic syndrome) what measures should be taken?

IV fluids and dialysis to flush STX from kidneys