Lecture 10 part 2 -- e.coli, shigella, salmonella

Question 1

what is the most common form of EHEC, responsible for most outbreaks of E. coli?

Answer 1

E. coli serovar O157:H7

Question 2

what is the major disease caused by EHEC?
explain it

Answer 2

mild to moderate colitis
we need less than 100 of EHEC bacteria to get colitis. this is why its the cause of a lot of outbreaks

the specific disease is called Hemolytic Uremic Syndrome (HUS)
it damages glomerular vessels, causes acute renal failure, thrombocytopenia, and CNS issues

Question 3

can EHEC get into the bloodstream?

Answer 3

the shiga toxin is what gets into the bloodstream to cause a variety of issues like renal failure and CNS issues

Question 4

what is the toxin of EHEC

Answer 4

shiga toxin (Stx)

Question 5

how are EHEC and EPEC similar?

Answer 5

they both produce A/E lesions (pedestals) in the host cell

Question 6

explain how the shiga toxin works.
which strain of e. coli has shiga toxin

Answer 6

EHEC

it is an AB exotoxin.

the B subunit binds Gb3 glycolipid
the A subunit blocks ribosomal 28S RNA which results in NO PROTEIN TRANSLATION by the host

Question 7

EAEC stands for what?
what kind of diarrhea does it cause?

Answer 7

enteroaggregative e. coli

causes protracted (long duration) of watery diarrhea

Question 8

besides EHEC, what other strain of E. coli produces shiga toxin? what does this mean?

Answer 8

EAEC also produces shiga toxin
this means it also causes HUS (hemolytic uremic syndrome)

Question 9

O:157H:7 is the strain of EHEC that causes most disease.
what is the most common form of EAEC that can also cause HUS?

Answer 9

O104:H4

Question 10

explain how EAEC work.
what is their adhesion protein?

Answer 10

adhesion protein = AAFI (aggregative adherence fimbriae I) which tightly binds to intestinal mucosa to form a “stacked brick” arrangement.

this stimulate mucus secretion to PROTECT THEMSELVES and a thick biofilm forms following QUORUM SENSING

Question 11

how can shigella get into our body?

Answer 11

through FECAL ORAL route – humans are the only reservoir

Question 12

true or false

all shigella serotypes have an exotoxin and it is the shigella toxin

Answer 12

yes

Question 13

there are over _______ serovars of salmonella

Answer 13

over 2000

Question 14

do shigella bacteria have pilli?

Answer 14

NO but they have adhesins

Question 15

do salmonella have pilli?

Answer 15

YES – type 1 pilli

Question 16

What are the 2 main diseases caused by all types of Shigella bacteria

Answer 16

Dysentery (intestinal infection) and HUS (hemolytic uremic syndrome)

Question 17

Shigella bacteria are biochemical variants of _____

Answer 17

E. coli (specifically EIEC – enteroinvasive E. coli)

Question 18

what are the 2 most relevant shigella species? which is the most common? which is the most severe?

Answer 18

shigella sonnei and shigella dysenteriae

more common = shigella sonnei
more severe = shigella dysenteriae

Question 19

how is shigella transmitted

Answer 19

ONLY fecal-oral route
humans are the only reservoir

Question 20

what is very unique about shigella

Answer 20

they replicate INTRACELLULAR and spread through cell-cell passage to avoid immune detection and clearance

Question 21

true or false

shigella infections spread easily throughout the body

Answer 21

FALSE – they are usually in a confined location. they move by moving to each individual neighboring cell

Question 22

shigella bacteria attach, invade, and replicate in cells lining the ____

Answer 22

colon

Question 23

what are the primary virulence factors of shigella

Answer 23

ipas – invasion plasmid antigens. injected through a type III secretion system

shiga toxin – disrupts protein synthesis, leading to intestinal epithelial cell damage.
B subunit binds Gb3 (glycolipid) on the host cell
A subunit cleaves 28s rRNA to prevent tRNA from binding to the “A” site of the ribosome

Question 24

how does shigella bacteria spread from cell to cell?

Answer 24

actin polymerization

Question 25

there are more than _____ unique serotypes for salmonella enterica

Answer 25

2500 (very common like e. coli)

Question 26

what are the 2 important salmonella human pathogenic serotypes?

Answer 26

salmonella typhi and salmonella paratyphi

Question 27

how is salmonella transmitted?

Answer 27

-ingestion of contaminated food
-fecal-oral route

Question 28

name a defining structural characteristic of a salmonella infection

Answer 28

formation of a pedestal that looks like a RUFFLE under a microscope

Question 29

how do shigella and salmonella have similar replication mechanisms?

Answer 29

they both replicate intracellularly

Question 30

true or false

SALMONELLA can cause either a transient or chronic infection

Answer 30

true

Question 31

how does salmonella get into the intestinal tissues?

Answer 31

through M cells

Question 32

does salmonella get into the blood?

Answer 32

YES
it is transocytised (ie: moves across the entire host cell to get into blood) and gets into the blood/lymph

Question 33

how does salmonella migrate and colonize efficiently

Answer 33

due to their pathogenicity islands I and II

Question 34

explain salmonellas pathogenicity island I

Answer 34

encodes for salmonella secreted invasion proteins (Ssps)

Question 35

explain salmonella pathogenicity island II

Answer 35

encodes for a type III secretion system to secrete various proteins and toxins

Question 36

name the clinical diseases caused by salmonella

Answer 36

MOST COMMON = gastroenteritis
septicemia
enteric fever

ASYMPTOMATIC COLONIZATION

Question 37

As mentioned, salmonella can cause septicemia.
who is most at risk for this

Answer 37

young, elderly, and immunocompromised

Question 38

typhoid fever is another word for

Answer 38

enteric fever

Question 39

explain how enteric fever happens

Answer 39

caused by salmonella
initial bacteremia with subsequent colonization of the GALLBLADDER and then REINFECTION of the intestines

Question 40

which bacteria can have ASYMPTOMATIC colonization

Answer 40

salmonells