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Essential Medical Science (UoL, Medicine) > EMS Microbiology > Flashcards

EMS Microbiology Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

What are Koch’s Postulates?

A

Causative organism must be isolated from every sufferer
Organism must be cultivated in pure culture
Typical symptoms must result in an individual inoculated
Organism must be recoverable from individuals infected

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2
Q

What are koch’s postulates for genes?

A

The gene encoding the trait of interest should be present and transcribed/translated in a virulent strain

The gene encoding the trait should not be present or should be silent in a strain that does not cause disease

Disruption of the gene should result in the formation of a strain that is incapable of causing disease

Introduction of the gene into a strain that did not cause disease should make it cause disease

Gene must be expressed in infection

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3
Q

What are some problems with Koch’s postulates?

A

Difficulty to isolate organisms
Ethical obligations
Animal models may be sufficient

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4
Q

What are some characteristics of viruses?

A

Intracellular parasites
Nucleic acid core wrapped in a protein coat made of capsomeres
Some have an envelope
Retroviruses are unusual

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5
Q

What are some characteristics of microfungi?

A 
Eukaryotic
Cell wall made up of chitin
Hairy growths are moulds
Moulds have tiny filaments known as hyphae that form mycelia
Mycelia subdivided by septa
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6
Q

What are the 4 classes of protozoa?

A

Apicomplexa
Flagellate Protista
Ciliate protista
Amoeba

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7
Q

Name some infections caused by protozoa?

A

Toxoplasmosis
Amoebic Meningitis
Malaria
Amoebic dysentery

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8
Q

What is mutualism?

A

Both organisms, in a symbiotic relationship, benefit

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9
Q

What is neutralism?

A

Neither organism, in a symbiotic relationship, derives benefit or harm

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10
Q

What is commensalism?

A

In a symbiotic relationship, one organism benefits and the other derives neither benefit nor harm

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11
Q

What is parasitism?

A

One organism, in a symbiotic relationship, benefits at the expense of the host

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12
Q

What is the difference between sterile and non sterile sites?

A

Sterile sites have no normal flora

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13
Q

How is sterility maintained?

A

Surface cleaning
Barriers that allow unidirectional flow
Physical separation from non sterile sites

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14
Q

What are some examples of sterile sites?

A 
Lower RT
Upper GT
Spinal cord
Meninges
Middle Ear
Urinary Tract
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15
Q

Coagulase Negative Staphylococci
Staphylococcus aureus
Propionibacterium acnes
Corynebacterium spp

Are examples of what?

A

Normal skin flora

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16
Q

Why is the skin difficult to colonise?

A

Variable temp
Dry
Aerobic environment
Nutrient Poor

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17
Q

Viridians
Oral strep
Anaerobes gram -ve and +ve
Candida spp

Are examples of what?

A

Normal mouth flora

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18
Q

Why are cavities in the mouth easy to colonise?

A

Constant temp
Moist
Rich nutrient source
Few physical challenges

19
Q

What organisms make up the normal nasopharyngeal flora?

A

Same as skin flora

20
Q

What organisms make up the normal flora of the pharynx?

A 
S. pyogenes
H. influenza
S. pneumonia
N. meningitides
S. aureus
M. catarhallis
21
Q

When does the flora of the vagina change?

A

Puberty

Addition of Lactobacillus spp to the normal skin flora

22
Q

What does lactobacillus spp do?

A

Ferment glycogen and maintain a pH of around 3

23
Q

What is the make up of flora in the stomach?

A

Low pH inhibits bacterial growth
Acid tolerant lactobacilli
H. pylori

24
Q

What happens to the amount of organisms as you descend through the GI?

A

They increase in number

25
Q

What are some characteristics of the flora of the large intestine?

A

Mostly anaerobes
Some aerobic bacteria such as enteric gram -ve bacilli
Milleri spp. also present

26
Q

What are the benefits of normal flora?

A

Synthesis and excretion of vitamins
Colonisation resistance
Induction of cross reactive antibodies

27
Q

Define pathogenicity

A

The capacity of an organism to cause infection

28
Q

What key factors does an organism require in order to cause an infection?

A

Transmissibility
Establishment in or on a host
Harmful effects
Persistence

29
Q

What are the 6 stages of infection?

A 
Pathogenic organism
Reservoir
Exit
Transmission
Entry
Susceptible host
30
Q

What is virulence?

A

The degree to which an organism can cause disease

31
Q

What is infectivity?

A

The ability of an organism to become established on or in a host via a microbial ligand or host cell receptor

32
Q

What is the virulence factor for bacteria?

A

Endotoxins

33
Q

What are some characteristics of endotoxins?

A

Components of the gram negative cell wall
Released from damaged/dead cells
Active component is lipopolysaccharide
Induce a range of uncontrolled host cell responses after binding to host cell receptors

34
Q

What is the host response to endotoxins?

A 
Systemic inflammatory response
Uncontrolled T Lymph response
Cytokine release
DIC
Cardiac and renal failure
35
Q

Botulism is a type of which virulence factor?

A

Exotoxin

36
Q

What is the mechanism of action of Clostridium botulinum?

A

Blocks ACh receptor and release of ACh causing a neuromuscular blocking effect

37
Q

What is the clinical presentation of botulism?

A 
Diplopia
Dysphagia
Dysarthria
Dry mouth
Death due to respiratory failure
38
Q

What exotoxin is produced in tetanus?

A

tetanospasmin

39
Q

What is the mechanism of action in tetanus?

A

Tetanospasmin binds to nerve synapses and inhibits the release of inhibitory neurotransmitters in the CNS causing a loss of inhibitory action on motor and autonomic neurons

40
Q

Cholera, diphtheria, C.diff, whooping cough - are all examples of what?

A

Exotoxin mediated infections

41
Q

Which virulence factors cause the following?

Break down of connective tissue
Inactivation of complement component C5a
Lyse blood cells

A

Hyaluronidase and streptokinase
C5a peptidase
Streptolycin -O and -H

42
Q

How does S. progenies evade the immune system?

A

M-protein binds fibrinogen and masks the bacterial surface which blocks complement binding and opsonisation

43
Q

This organism has a polysaccharide capsule which inhibits opsonisation and therefore phagocytosis

A

S.Pneumonia

Essential Medical Science (UoL, Medicine) (9 decks)

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