Bacteria - Week 2

Question 1

Is bacteria a prokaryote or eukaryote?

Answer 1

Prokaryote

Question 2

Describe the cell wall of a Gram+ bacteria

Answer 2

Thick layer of peptidoglycans containing teichoic acid and lipoteichoic acid (acts as a PAMP). Crystal violet dye stains it purple.

Question 3

Describe the cell wall of a Gram- bacteria

Answer 3

Thin layer of peptidoglycan. Additional outer layer rich in lipopolysaccharides (antigen that interacts with TLR-4). Crystal violet dye stains it pink.

Question 4

What does it mean by acid-fast bacteria? Give an example

Answer 4

Characterised by wax-like cell wall that contains mycolic acid.
Gram+ mycobacteria

Question 5

What is it meant by fastidious bacteria?

Answer 5

Bacteria that will only grow if certain nutrients are present

Question 6

What shape is a cocci, bacilli and spirilla?

Answer 6

Spherical, rods, helical

Question 7

Describe the phases of growth you’d see in bacterial numbers when added to a culture medium

Answer 7

lag phase > logarithmic/exponential phase (population doubles at constant rate) > stationary phase > death

Question 8

What is the term used to describe how bacteria reproduce?

Answer 8

Binary fission - where one bacterial cell divides into two identical daughter cells

Question 9

Briefly describe the process of transformation

Answer 9

ability to take up DNA fragments from related spp. across cell wall

Question 10

Describe transduction

Answer 10

transfer of genetic material by infection with bacteriophage

Question 11

conjugation

Answer 11

bacterial ‘mating’ where DNA is transferred from one bacterium to another by use of a pilus

Question 12

List Koch’s Postulates

Answer 12

1) microbe must be present in all cases of the disease
2) pathogen can be isolated from diseased host and grown in pure culture
3) pathogen from pure culture causes disease when inoculated into a health, susceptible lab animal
4) pathogen can be re-isolated from new host and shown to be same as originally inoculated pathogen

Question 13

what is a facultative aerobe?

Answer 13

organism that makes ATP by aerobic resp. when O2 present but can switch to anaerobic resp. if O2 is absent

Question 14

Obligate aerobe

Answer 14

cannot make ATP in absence of oxygen

Question 15

obligate anaerobe

Answer 15

dies in presence of o2

Question 16

Overt/strict pathogen

Answer 16

only associated with human disease - not found in healthy microbial flora

Question 17

opportunistic pathogen

Answer 17

present in normal gut flora but only causes disease when introduced into unprotected site (e.g. in immunocompromised patients)

Question 18

facultative pathogen

Answer 18

can grow and survive in environment as well as in host

Question 19

Give examples of bacterial virulence factors

Answer 19

1) adhesins (pili, outer membrane proteins)
2) flagella
3) toxins
4) capsule
5) type III secreted molecules

Question 20

What is an endotoxin

Answer 20

part of LPS of cell wall of Gram- bacteria. Heat stable, cell bound. causes general symptoms such as fever, diarrhoea, vomiting. weakly toxic

Question 21

What is an exotoxin

Answer 21

proteins produced extracellularly by certain Gr+ and Gr- spp. Heat labile, usually highly toxic

Question 22

enterotoxin

Answer 22

group of exotoxins that acto on small intestine. (C.difficile toxin A)

Question 23

What is a toxoid?

Answer 23

Inactivated toxin - useful as a vaccine

Question 24

List various methods of bacterial immune evasion

Answer 24

1) Hide - enter cell and stay intracellular
2) antigenic variation - avoid an established immune response
3) Molecular mimicry - so body recognises it as self
4) modify or block host immune response - e.g. interfere with host’s cell signalling pathways - type III secreted effectors

Question 25

What is meant by commensal bacteria? Where would you find them?

Answer 25

living in relationship with another organism where one derives benefits from another organism withough hurting or helping it.
Find in normal microbial flora

Question 26

What factors can affect the human microbiiome?

Answer 26

diet, age, genetics, lifestyle, immune response, microbial co-adaptation, drugs

Question 27

List some of the positive effects of the gut microbiome

Answer 27

• develop/stimulate immune system
• prevent colonisation of pathogens
• produce beneficial nutrients (e.g. vit. K)
• metabolise natural compounds into more readily available versions
• metabolise xenobiotic substances, destroying toxins

Question 28

Name a microbe that is present in normal gut flora but that can cause antibiotic-associated diarrhoea in hospitalized patients

Answer 28

Clostridium difficile.

Gr+, anaerobic

Question 29

What substance in the GI tract keeps vegetative growth of C.diff at bay?

Answer 29

Secondary bile salts

Question 30

What substance in the GI tract allow C.diff spores to turn into a vegetative state?

Answer 30

Primary bile salts

Question 31

what is the term used to describe an imbalance of the normal gut microbiota composition

Answer 31

Dysbiosis

Question 32

What are pre-biotics?

Answer 32

non-digestible food ingredient that beneficially affects the host by selevtively stimulating the growth and/or activity of one or a limited number of bacteria in the colon to improve host’s health

Question 33

What are probiotics

Answer 33

living, non-pathogenic organisms used as food ingredients to benefit the hosts’ health