Lecture 8-9 Gram negative bacteria (Part 2)

Question 1

Shigellosis is primarily a disease in what age group?

Answer 1

Children

Question 2

Is the infectious dose of Shigella large or small and why?

Answer 2

Small. They are very acid resistant and are able to survive the stomach acid ‘sterilization process’.

Question 3

What 2 main methods are used by Shigella to cause shigellosis?

Answer 3

1. Infecting the mucosal epithelium of the colon by bacterial-directed endocytosis of M-cells (specialized phagocytic cells of the gut)
2. They also can induce formation of actin-directed pseudopodia that thrust bacteria directly into adjacent mucosal epithelial cells without exposure to plasma proteins or phagocytic cells.

Question 4

Is the infection local or systemic with Shigella?

Answer 4

Local. Local inflammatory ulceration of mucosal cells creates blood and pus in the stool. (dysentery)

Question 5

What is the Shiga toxin?

Answer 5

An A-B toxin that cleaves ribosomal RNA, disrupting protein production in the cell.

Question 6

What is the primary manifestation of Shiga toxin?

Answer 6

Damage to the intestinal epithelial cells.

Question 7

What is Hemolytic Uremic Syndrome?

Answer 7

In a small number of patients (mainly young children), the shiga toxin gets into the blood stream in high enough concentration where it mediates damage primarily to the glomerular endothelial cells, resulting in renal failure. (Systemic)

Question 8

What E. coli strain also contains a plasmid encoding a Shiga-like Toxin?

Answer 8

EHEC

Question 9

Where does Shigella infect

Answer 9

Colon

Question 10

Where does Salmonella infect?

Answer 10

The G.I. mucosa similar to Shigella

Question 11

How does Salmonella typhi act?

Answer 11

It can break through the Gut epithelium and enter phagocytic cells which then act as Macrophage Taxis to take the pathogens throughout the body.

Question 12

What the is the method by which enteric gram negative bacteria are spread throughout the body after inserting themselves inside the macrophage.

Answer 12

1. They block lysosome fusion and multiply within the phagosome of machrophages
2. Hitch a ride into draining lymph nodes, bloodstream, or other tissues (all while being protected from immune system)
3. released upon the death of the macrophage causing bacteremia and infection.

Question 13

Enteric Fever caused by bacteremia is also called what?

Answer 13

Typhoid Fever

Question 14

Typhoid Mary was an example of what?

Answer 14

A permanent carrier of Typhoid fever

Question 15

Most infections of Salmonella result from what?

Answer 15

Ingestion of contaminated food products

Question 16

What age group does Salmonella infections affect?

Answer 16

All age groups

Question 17

Is the infectious dose small or large for Salmonella and Why?

Answer 17

Large. Salmonella is very sensitive to stomach acid and requires a large does to become infected. This is contrary to Shigella

Question 18

Is Salmonella infection local or systemic?

Answer 18

generally causes a localized infection of the small intestine mucosal epithelium.

Question 19

How does the normal GI flora E. coli become pathogenic?

Answer 19

Genes that code for virulence factors can be transferred to non-pathogens including common GI normal flora such as E. Coli

Question 20

Name the four pathogenic strains of E. coli

Answer 20

Enterotoxigenic E. Coli (ETEC)
Enterohemorrhagic E. coli (EHEC O157:H7)
Enteropathogenic E. coli (EPEC)
Enteroinvasive E. coli (EIEC)

Question 21

2 characteristics of ETEC?

Answer 21

V. cholera exotoxin gene

Watery diarrhea

Question 22

3 characteristics of EHEC?

Answer 22

Shiga-like exotoxin gene
Bloody dysentery
Hemolytic Uremic Syndrome (HUS)

Question 23

3 characteristics of EPEC?

Answer 23

Shigella exotoxin gene
Adherence gene
Diarrhea

Question 24

2 characteristics of EIEC?

Answer 24

Invasive genes

Dysentery

Question 25

Most gram negative rods that produce UTIs originate where?

Answer 25

In the colon, contaminate the urethra and ascend into the bladder

Question 26

UTI is an ____________ infection

Answer 26

Ascending

Question 27

What is the most common cause of UTIs and why?

Answer 27

Uropathogenic strains of E. coli

They produce specialized adhesions that allow them to adhere within the urinary track.

Question 28

What bacteria causes Plague rather than a GI infection in humans?

Answer 28

Yersinia pestis

Question 29

Yersinia pestis causes a local or systemic infection?

Answer 29

Systemic with a high mortality rate.

Question 30

What type of host are humans considered to be in Y. pestis infections

Answer 30

Accidental hosts. Infections are primarily Zoonotic

Question 31

What are the typical hosts for Y. pestis

Answer 31

Rats, rodents and fleas

Question 32

How is Y. pestis spread from a flea?

Answer 32

The bacteria replicate rapidly in the midgut of the flea. They eventually block the midgut and the next time the flea feeds it regurgitates into the fleabite.

Question 33

What main exotoxin is used in Y. pestis

Answer 33

Superantigen

Question 34

What is a necrotic bubo?

Answer 34

A dead lymph node which is a result of Y. pestis quickly replicating in a lymph node

Question 35

What occurs with Y. pestis if the primary infection occurs in the lung?

Answer 35

Pneumonic plague

Question 36

Immunity to cholera is a good example of what?

Answer 36

the value of maternal passive immunity

Question 37

Is Vibrio Cholera resistant or sensitive to stomach acid?

Answer 37

Sensitive

Question 38

Is Vibrio cholera invasive or non-invasive?

Answer 38

Non-invasive

Question 39

What is the result of an infection of V. cholera?

Answer 39

A-B toxin enters the cells and activates adenylate cyclase, resulting in hypersecretion of water and electrolytes. Mortality rate falls from 60% in infants to 1% if promptly treated with replacement fluids and electrolytes

Question 40

T or F, Antibiotics are secondary to fluids in a V. cholera infection/

Answer 40

True

Question 41

What is the danger of synthetic infant milk formulas in some parts of the world?

Answer 41

In some communities sIgA immunity provided by mother’s milk is the only defense in babies against contaminated water and food. Synthetic infant milk formulas do not provide this protection.

Question 42

Babies are most vulnerable to pathogens during what time?

Answer 42

During the “window of susceptibility”. This is a time when the maternal IgG is largely lost while the neonatal IgG levels are still low