Bacteria

Question 1

Meaning: opportunistic pathogen

Answer 1

A pathogen that currently lives in body’s flora but transits to further places to cause disease.

Question 2

Meaning: pathogenicity

Answer 2

The ability to cause a disease.

Question 3

Virulence

Answer 3

The degree/intensity of pathogenicity defined by invasiveness, infect ivory and pathogenic potential.

Question 4

Virulence factor

Answer 4

Biological product that contributes to virulence or pathogenicity

Question 5

Pathogenesis

Answer 5

Strategy, mechanism of process by which disease develops

Question 6

Primary pathogen

Answer 6

Directly caused disease

Question 7

Latent disease

Answer 7

Periods of inactivity alternate with obvious symptoms, low severity

Question 8

Acute disease

Answer 8

High severity develops and resolves rapidly.

Question 9

Chronic disease

Answer 9

Low severity, develops slowly and persists.

Question 10

Difference between Gram negative and Gram positive

Answer 10

Gram positive have thick peptidoglycan layer (100 layers) with lipoteichnoic and teichnoic acids in it. Molecules are able to diffuse through the peptidoglycan layer to the plasma membrane below. Original stain is more resistant to washing so it stays

Gram negative: thin peptidoglycan layer (6 layers) peri plasmid space between outer lipopolysaccharide membrane and peptidoglycan wall). Outer lipopolysaccharide membrane (non energised) with poring to allow molecules to diffuse in and out. The original stain washes off so the second stain is shown.

Question 11

What are the main characteristics of a prokaryote?

Answer 11

• Absence of nuclear membrane or discrete nucleus
• single circular DNA chromosome
• plasmids present
• reproduce via binary fission (not mitosis)
• complex cell wall

Question 12

What are the main bacterial shapes and examples of each?

Answer 12

Bacilli rods: E. Coli, Shigella, Clostridium.
Cocci: staphylococcus (clusters) and streptococcus (chains)
Spiral: H. Pylori
Comma-shaped: Vibrio Cholerae.

Question 13

3 bacterial extra cellular structures and their functions?

Answer 13

• Capsule (extra cellular polysaccharides): prevents dessication (drying out), resists phagocytosis, maintains key hydrolytic enzymes close to the cell, adhesion to surfaces.
• Fimbriae/pilli: attachment (not motility).
• Flagella: motility.

Question 14

What are the components of a usual bacterial genome?

Answer 14

-singular circular dsDNA chromosome NOT complexed with histones and plasmid DNA (extra-chromosomal DNA that can vary in size and copy number).

Question 15

What are the characteristics of plasmids?

Answer 15

• extra chromosomal DNA
• contains non-essential genes that confer selective advantage
• exist and replicate independently of chromosomes
• usually small, closed circular DNA.

Question 16

5 main factors that control the growth of bacteria

Answer 16

Temperature, pH, external osmolarity, oxygen, nutrient concentration.

Question 17

Four distinct phases of bacterial population growth?

Answer 17

• lag phase: fellas adapt to new conditions, enzymes and new metabolites accumulate
• exponential phase: maximum constant growth phase
• stationary phase: slow death of cells balanced by slow multiplication due to insufficient oxygen/nutrient supply.
• death phase: sharp drop in number of viable cells.

Question 18

3 broad types of nutrient media and why are they useful?

Answer 18

• Enrichment: allows growth of many types of bacteria.
• Selective: allows growth of selected group of bacteria only.
• Differential: allows growth of a number of types of bacteria BUT colonies develop with defined characteristics.

Question 19

When is the microbiome established and what is its function?

Answer 19

Established in the first few months of life and effects human cell function and immune system balance.

Question 20

Some examples that the microbiome in human tissue is related to?

Answer 20

IBD (Crohn’s), childhood asthma, allergy development, colorectal and gastric cancer, obesity, type 2 diabetes mellitus, COPD, cystic fibrosis.

Question 21

What are the two major virulence factor and give examples of each?

Answer 21

• Products that promote capacity to establish infection (competition with endogenous micro flora) e.g. Adherence to host mucosa, scavenging of essential nutrients. Resistance to host defences e.g. Survive within the host.
• products that damage host and cause symptoms e.g. Hydrolytic enzymes, toxins, mediators of host inflammatory responses.

Question 22

3 methods of DNA transfer between and among bacteria.

Answer 22

Transformation: plasmid of free DNA
Conjugation: direct transfer via cell-cell contact
Transduction: transfer via bacterial viruses.

Question 23

Distinguish between Pathogenesis, pathogenicity and virulence.

Answer 23

Pathogenesis is the mechanism or process by which bacteria causes disease.
Pathogenicity is the ability of the pathogen to cause disease.
Virulence is the severity of a pathogens ability to cause disease.

Question 24

What are the steps in bacterial Pathogenesis?

Answer 24

1. Transmission: from host to reservoir.
2. Colonisation: adherence and invasion of usually mucosal surfaces.
3. Proliferation: within host/invasion (host provides nutrients).
4. Evasion: of host immune system
5. Transmission to another host/reservoir.

Question 25

What factors influence virulence?

Answer 25

Invasiveness, infectivity and damage to host.

Question 26

What are the features of a biofilm?

Answer 26

• antibiotic tolerant
• evade the immune system
• chronic/persistent infections.

Question 27

What are the features of bacteria writhing a biofilm?

Answer 27

• Heterogenous population
• active stress response
• metabolically slow

Question 28

Distinguish between exotoxins and endotoxins.

Answer 28

Exotoxins: soluble, released by bacteria and tissue specific.
Endotoxins: part of bacterial structure e.g. LPS. They’re released when the bacteria die, induce over-active immune response.