Lecture 8-9 Gram negative bacteria

Question 1

Gram negative rods are a major part of our normal flora especially where in our body?

Answer 1

Gut

Question 2

What are the 5 F’s for transferring infection

Answer 2

Food, Fluids, Fingers, Flies and Feces

Question 3

Explain the most important characteristic of Enteric Gram negative rods that deals with virulence factors

Answer 3

These bacteria are able to ‘share’ virulence factors by gene transfer via plasmids, conjugation, transformation, or by bacteriophage transduction.

Question 4

The “sharing” of virulence factors in Enteric Gram negative rods leads to what?

Answer 4

Spread of antibiotic resistance among pathogens and produces variant strains of typically normal flora.

Question 5

Define Zoonotic

Answer 5

a disease or microbe that normally exists in other animals, but can be transmitted and infect humans.

Question 6

Name 5 diseases that enteric gram - bacteria can cause

Answer 6

1. GI infections (diarrhea, colitis, etc.)
2. Food “poisoning”
3. Urinary Track Infections (Major Cause 75%)
4. Sepsis & Bacteremia
5. Ulcers & Gastritis

Question 7

4 major characteristics of Enteric Gram- Rods

Answer 7

1. Non-fastidious (but sensitive to drying)
2. Metabolically diverse
3. Facultative Anaerobes
4. Normally found in GI tract of humans and other animals

Question 8

Name the 4 enteric g- bacteria that are a part of our normal flora

Answer 8

Escherichia coli
Klebsiella
Proteus
Bacteroides

Question 9

Describe the three designations give to these bacteria for serological typing

Answer 9

Flagella = H-antigens
Capsules = K-antigens
Endotoxins = O-antigens

Question 10

What is Antigen Variation

Answer 10

Often multiple genes are available for each antigen, and an individual bacterium can change back and forth between these genes to change the epitopes on the cell surface. This is very helpful to evade the adaptive immune response!!!!

Question 11

What is macrophage taxis?

Answer 11

Where bacteria can grow and survive inside the macrophage. It is then transported throughout the body.

Question 12

What is the use of Adhesions in enteric g- bacteria

Answer 12

These bacteria must adhere firmly to surface mucosal sites because of the innate flushing that occurs in the gut. These adhesins (often fimbrae-associated) determin where the bacteria binds.
It is also sometimes a cause of pathology

Question 13

What is bacterial-directed endocytosis and how is it used in enteric g- bacteria?

Answer 13

Some species of bacteria can actually initiate actin assembly and commence their own internalization into the cells they attach to. Some strains enter the cytoplasm of cells (Shigella and E. coli) while others enter the macrophages (Salmonella and Yersinia)

Question 14

How do Salmonella and Yersinia use bacterial-directed endocytosis differently than E. coli and Shigella?

Answer 14

Salmonella and Yersinia invade mucosal epithelium and enter MACROPHAGES.
E. coli (EIEC strain) and Shigella enter muscoal epithelium and divide in the CYTOPLASM of those cells.

Question 15

EPEC strains of E. coli use adhesions in what specific way which causes what dysfunction?

Answer 15

They attach to gut epithelial cells and cause the microvillus structure to become altered, causing malabsorption. They flatten and destroy the microvilli.

Question 16

T or F, Endotoxins are the LPS layer found in ALL gram negative bacteria

Answer 16

True

Question 17

What is the method by which endotoxins or LPS works?

Answer 17

LPS causes massive activation of macrophages (and other cells) resulting in production of huge amounts of pro-inflammatory cytokine mediators such as IL-1 and TNF-alpha.
TNF-alpha stimulates endothelial cells to produce NO that causes pre-capillary sphincters to relax and capillary beds to open.

Question 18

What happens when Gram negative bacteria enter the body in SMALL numbers

Answer 18

They are aggressively attacked by our entire innate inflammatory system with waiting for an adaptive immune response. LPS activates macrophages, Platelets, hageman factor and alternate complement pathway

Question 19

If Gram negative is present in the blood stream in LARGE numbers what happens?

Answer 19

Initiates a massive inflammatory response that causes Sepsis (too much inflammation in body), which can be quickly fatal.

• Hypovolemic Shock
• Disseminated intravascular coagulation

Question 20

What characteristic produces unique pathogenic strains of otherwise normal enteric g- bacteria?

Answer 20

Variety of exotoxins produced by genes that are often acquired and transferred via conjugation plasmids or by bacteriophage transduction.

Question 21

What is the main protein exotoxin secreted by enteric g- bacteria

Answer 21

Mostly A-B exotoxin

Question 22

3 major classes of A-B exotoxins that are produced by enteric gram - pathogens

Answer 22

• Two A-B enterotoxins that cause ribosylation of regulatory proteins in gut epithelial cells
• An A-B toxin that cleaves ribosomal RNA, thus blocking protein synthesis mainly within endothelial cells of kidney and CNS

Question 23

What is the most common method of transfer for enteric gram negative bacteria

Answer 23

Fecal-Oral route (the 5 F’s with emphasis on feces)

Question 24

What is one of the major ways to test whether drinking water has been contaminated with fecal materials?

Answer 24

Assay for the presence of enteric gram negative rods, especially E. coli, in water

Question 25

What is the disease causing potential

Answer 25

(Virulence X Dose)/ Host Resistance

Question 26

T or F, Diseases caused by enteric gram negative rods tend to decrease during the summer

Answer 26

False, They increase