MoD: Microbiology

Question 1

What is the purpose of the capsule or slime layer around bacteria?

Answer 1

Polysaccharide material protecting bacteria from phagocytosis, dessication, immune attack and antibiotics.

Question 2

What is the difference between capsule and slime layer in bacteria?

Answer 2

Capsule= a semi-ridged border around the cell, which excludes India Ink when dyed.
Slime layer= non-ridged matrix easily deformed and cannot exclude India Ink

Question 3

What is a gram-stain test in bacteria?

Answer 3

An ability to retain a crystal violet-iodine complex when cells are treated with acetone or alcohol. It detects peptidoglycan (in the cell walls of gram-positive bacteria)
So gram-positive bacteria retain the dye (stain violet) while gram-negative bacteria dont.

Question 4

A common gram +ve cocci?

Answer 4

Staphylococcus aureus (MRSA)
Streptococcus pyogenes (sore throat, rheumatoid fever)

Question 5

A common gram -ve bacilli?

Answer 5

Salmonella typhi
E. Coli
Yersinia pestis (plaques)

Question 6

4 methods of bacterial replication?

Answer 6

1- Binary fission
2- Conjugation
3- Transformation
4- Transduction

Question 7

What is binary fission?

Answer 7

Cells divide to give two identical daughter cells. Asexual, no exchange of genetic material.

Question 8

What is conjugation? (in bacterial replication)

Answer 8

The transfer of transposable elements, use of conjugation tube (sex pilus) connects two bacteria, and some genetic diversity.

Question 9

What is transformation? (in bacterial replication)

Answer 9

Picking up genetic material from the environment (such as plasmids).
Creates no new bacteria, introduces some genetic diversity into population.

Question 10

What is transduction? (in bacterial replication)

Answer 10

Transfer of genetic material via a viral vector.

Introduces some genetic diversity into population

Question 11

Components of viruses?

Answer 11

• Nucleic Acid= DNA/RNA, double/single stranded, sense/antisense
• Capsid= protein coat
• Envelope= lipid, derived from host
• Virus Proteins= viral encoded, protein/glycoprotein

Question 12

5 stages of viral replication?

Answer 12

1) Attachment/ penetration
2) Uncoating (genome released from capsid, genetic material targeted to nucleus)
3) Early viral proteins produced (using cellular machinery for transcription)
4) Virion Assembly
5) Virion Release

Question 13

2 types of virion release used in viral replication?

Answer 13

1- Lytic= ‘bursts’ cell releasing virions

2- Lysogenic= integrate into host cell DNA and replicate along with host cells.

Question 14

What are prions?

Answer 14

eg) Creutzfeldt-Jakob Disease, Scrapie
- Misfolded protein
- No genetic material
- Can be inherited, spread via contaminated material or occur spontaneously.

Question 15

What is symbiosis?

Answer 15

Two or more organisms co-exist in close physical association

Question 16

Types of symbiosis? (4)

Answer 16

1- Mutualism (both organisms benefit, eg Nitrogen-fixating bacteria and legumes)
2- Neutralism (no benefit or harm)
3- Commensalism (one organism benefits, the other derives neither benefit or harm)
4- Parasitism

Question 17

Why is metabolism a benefit of normal flora?

Answer 17

Synthesis of secondary metabolites/ vitamins…
eg) vitamins K and B12 secreted by enteric bacteria (E. Coli in colon produces vit K for blood clotting and bone metabolism)
Fermenting unused energy substrates (short chain fatty acids)

Question 18

What are the benefits of oral microbiota?

Answer 18

Nitric Acid production… 25% ingested nitrate returned to mouth. Oral bacteria reduce nitrate to nitrite, which is absorbed and converted to nitric oxide. This is essential for vascular health.

Question 19

What may faecal transplant treatment have a positive effect on?

Answer 19

• Multiple Sclerosis
• Chronic Fatigue syndrome (ME)
• Ulcerative Colitis
• IBD
• Diabetes mellitus
• Clostridium difficile infection (hospital acquired)

Question 20

Define Pathogenicity?

Answer 20

The capacity of a micro-organism to cause an infection

Question 21

Define Virulence?

Answer 21

The degree to which a micro-organism is able to cause disease

Question 22

What are the 6 Virulence factors?

Answer 22

1- Facilitation of adhesion
2- Toxic effects
3- Tissue-damage
4- Interference with host defence mechanisms
5- Facilitation of invasion
6- Modulation of host cytokine responses

Question 23

Define infectivity?

Answer 23

The ability of a micro-organism to become established on/in a host. Requires a microbial ligand and a host cell surface receptor.

Question 24

Routes of transmission of a pathogen?

Answer 24

• Faecal-oral (C. dif, cholera, typhoid)
• Blood borne (Hep B,C and HIV)
• Respiratory
• Direct contact

Question 25

Botulism (EXOTOXIN)

a) causes?
b) how is it presented clinically?

Answer 25

Botulism (clostridium botulinum)- binds presynaptically on cholinergic nerve terminals and decreases release of acetylcholine.

a) Ingestion of pre-formed toxin (food), infection of dirty wounds, GI colonisation
b) Diplopia, dysphagia, dysarthria, dry mouth, death (paralysis of muscles of respiration)

Question 26

Tetanus (EXOTOXIN)

a) causes?
b) mechanism?

Answer 26

Tetanus (Clostridium tetani), another neurotoxin but causes a rigid paralysis rather than flaccid paralysis (like in botulism)

a) infection of dirty wounds
b) binds to nerve synapses and inhibits release of inhibitory neurotransmitters in CNS (death by respiratory paralysis)