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Phase 2 > Microbiology & Infectious Diseases > Flashcards

Microbiology & Infectious Diseases Flashcards

1
Q

What is a virus?
Briefly describe its structure

A

An infectious, obligate intracellular parasite
Comprised of genetic material (DNA OR RNA) surrounded by a protein coat and/or a membrane

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2
Q

Big difference between Virus and Bacteria?

A

Virus IS dependent on host cell (bacteria is not)

Bacteria has cell wall, organelles, DNA AND RNA and are alive
Viruses have none of these things and are not alive

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3
Q

When virus is outside the cell, what is it called?

A

Virion?

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4
Q

How do viruses replicate?
Describe the 6 stages

A
  1. Attachment to specific receptor on host cell
  2. Cell entry - only central viral core (carrying the nucleic acids and some proteins) enters host cell
  3. Interaction with host cells - uses cell materials (e.g. enzymes, amino acids) for their replication
  4. Replication may localise in nucleus, cytoplasm or both
  5. Assembly - occurs in nucleus, cytoplasm or cell membrane
  6. Release - bursting open of cells OR leaking from cell over period of time
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5
Q

How do viruses cause disease?
Give examples

A

Damage by :
- direct destruction of host cells e.g. HIV
- modification of host cell structure or function e.g. rotavirus
- over-reactivity of host host as response to infection e.g. hepatitis
- cell proliferation and cell immortalisation e.g. HPV
- evasion of extra AND intracellular host defences

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6
Q

What is a pathogen?

A

Organism that causes or is capable of causing disease

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7
Q

What is a commensal?

A

Organisms which colonises the host BUT causes no disease in normal circumstances

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8
Q

What is an opportunist pathogen?

A

Microbe that only causes disease if host defences are compromised

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9
Q

Define virulence / pathogenicity

A

Ability to cause disease once established

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10
Q

What is asymptomatic carriage?

A

When a pathogen is carried harmlessly at a tissue site where it causes no disease

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11
Q

What do gram negative bacteria have that gram positive don’t?

A

DOUBLE CELL MEMBRANE
2 membranes separated by lipoprotein, periplasmic space and petidoglycan

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12
Q

State and describe the types of bacterial toxins

A

ENDOTOXIN - part of outer membrane of bacteria

EXOTOXIN - proteins secreted by gram pos and neg bacteria

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13
Q

What does the coagulase test distinguish?

A

Distinguishes S.aureus from other staph
- will be COAGULASE POSITIVE

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14
Q

Types of gene mutation

A

Base sub
Deletion
Transfer

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15
Q

Types of gene transfer

A

Transformation e.g. plasmid
Transfunction e.g. via phage
Conjugation e.g. via sex pilus

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16
Q

Describe how to gram stain

A
  1. Apply primary stain (crystal violet) to heat fixed bacteria
  2. Add IODIDE - binds to crystal violet and fixes it to cell wall
  3. DECOLOURISE with ethanol or acetone
  4. COUNTERSTAIN with safranin (pink)
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17
Q

What does gamma haemolysis imply?

A

NO haemolysis

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18
Q

Why does alpha haemolysis occur?
How does the agar appear?

A

BC production of hydrogen peroxide oxidising haemoglobin
GREEN

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19
Q

Why does beta haemolysis occur?

A

Bc lysis of RBCs by haemolysis such as Streptolysin O produced by S. pyogenes

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20
Q

What does an oxidase test test for?

A

If micro-organisms contains a cytochrome oxidase
implies organism able to use O2 as terminal e- acceptor

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21
Q

Gram pos bacteria stain what colour?
Give an example

A

PURPLE
Staph. Aureus - coagulase positive

22
Q

What are the groups of Streptococci classification?

A
  1. Haemolysis
  2. Lancefield typing
  3. Biochemical properties
23
Q

What is lancefield grouping?

A

A method of grouping catalyse neg, coagulase neg bacteria
Based on bacterial carbohydrate cell surface antigens

24
Q

How do gram-pos bacteria spread?

A

Aerosols, surface-to-surface, colonisation of prostheses

25
Q

Virulence factors of Gram Neg bacteria?

A
  1. Colonisation factors - adhesins, invasins
  2. Toxins (effectors) - usually secreted proteins - damage, subversion
26
Q

Name the 4 major groups of Gram-Neg bacteria
Describe their shape

A
  1. Proteobacteria - ALL rod-shaped
  2. Bacteroids - rodshaped
  3. Chlamydia - round pleimorphic
  4. Spirochaetes - spiral/helical
27
Q

Why can is be difficult to culture pathogens in the lab?

A

Bc of dependency on host

28
Q

3 Types of Worms

A
  1. Nematodes (roundworms)
  2. Trematodes (flatworms)
  3. Cestodes (tapeworms)
29
Q

What type of nematodes can you get?

A

Intestinal
Larva migrans
Tissue (filaria)

30
Q

What type of trematodes can you get?

A

Blood
Liver
Lung
Intestinal

31
Q

What type of cestodes can you get?

A

Non-invasive
Invasive

32
Q

What is the pre-patent period?

A

Interval between infection and appearance of eggs in the stool

33
Q

What is a protozoa?

A

Single-celled eukaryotic organism with a definitive nucleus

34
Q

Name medically important mycobacteria

A

M. TB
M. leprae - leprosy
M. avium - disseminated infection in AIDS
M.kansasii - chronic lung infection
M.marinum - fish tank granuloma
M.ulcerans - buruli ulcer
Rapidly growing mycobacteria

35
Q

What is a Mycobacteria?

A

Aerobic, non-spore forming, non-motile bacillus

Slow reproduction
Slow response to treatment
Slow growing ∴ hard to culture

36
Q

Describe the cell wall of Mycobacteria

A

Contains high molecular weight lipids
Weakly gram-pos (or colourless)
Survive inside macrophages, even in low pH environments

37
Q

What is acid fast bacilli used for?

A

To identify organisms with wax-like, thick cell walls
E.G. MYCOBACTERIA (which are resistance to gram stain)

38
Q

Name some direct lab methods to diagnose bacterial infections

A

Gram stain
Acid fast stains
Wet film
KOH (fungi)
India ink

39
Q

Name some culture lab methods to diagnose bacterial infections

A

Solid media
Liquid media
Blood culture

40
Q

How do fungi move?

A

By growth or through generation of spores - carried thru air/water

41
Q

Describe fungi

A

Eukaryotic
Chitinous cell wall
Heterotrophic

42
Q

What is a dimorphic fungi?

A

Fungus that exists as both yeast and mould - switches between the 2 when conditions suit

43
Q

What are yeasts?

A

Small single celled organisms that divide by budding

44
Q

What do moulds form?

A

Multicellular hyphae and spores

45
Q

What does selective toxicity in treating fungal disease rely on?

A

Target does not exist in humans
Target is signif different to human analogues
Drug is conc in organism cell (respect to humans)
↑ permeability to compound
Human cells being ‘rescued’ from toxicity by alternative metabolic pathways

46
Q

Why can fungi be hard to treat?

A

Relatively few classes of effective antifungals

47
Q

Why can the total worm burden in a human not increase (unless constant re-exposure)?

A

Bc adult worms can’t reproduce in the body (without a period of development outside) ∴ if worm can’t get out, it will die

Can produce larvae/eggs but once grown, will die

48
Q

Define invasiveness

A

Capacity to penetrate mucosal surfaces to reach normally sterile sites

49
Q

5 Major groups of protozoa

A

Flagellates
Amoebae
Sporozoans
Ciliates
Microsporidia

50
Q
A

Phase 2 (24 decks)

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