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principles of disease > medical microbiology week 5 > Flashcards

medical microbiology week 5 Flashcards

1
Q

what are some microbial causes of infection

A
  1. bacteria (prokaryotic)
  2. viruses (unclassified)
  3. fungi (eukaryotic)
  4. parasites (usually eukaryotic)
  5. prions (unclassified)
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2
Q

what is a prion

A

protein of unknown function that resides on the surface of brain cells

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3
Q

what’s bigger a prion or a virus

A

virus

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4
Q

what’s bigger a bacteria or a virus

A

bacteria

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5
Q

what’s bigger a fungi or a bacteria

A

fungi

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6
Q

in microscopy when would you not use a stain

A
  • to see white blood cells (e.g. urine)

- to see parasites (e.g. faeces)

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7
Q

in microscopy when would you use a stain

A

to visualise bacteria and yeasts/fungi

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8
Q

can you see viruses in light microscope

A

no

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9
Q

how do you detect viruses in clinical samples

A 
molecular methods
- real time/PCR
- antigen detection
- serology to determine immunity 
virtually obsolete methods 
- electron microscopy
- cell or tissue culture
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10
Q

how is parasite diagnosed

A
  • microscopy of different life cycle stages
  • culture rarely possible
  • serology sometimes useful
  • reference laboratories
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11
Q

what characteristics do bacterial cells have

A
  • capsule
  • cell wall
  • single chromosome
  • no nucleus
  • flagellum
  • fimbriae
  • ribosomes
  • plasma membrane
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12
Q

what is the outer membrane on a bacterial cell

A

component of the gram negative cell wall

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13
Q

is a gram positive cell wall thin or thick

A

thick

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14
Q

is a gram negative cell wall thin or thick

A

thin

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15
Q

what does a gram positive cell wall contain

A
  • plasma membrane with proteins
  • then periplasmic space
  • then peptidoglycan
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16
Q

what does a gram negative cell wall contain

A
  • plasma membrane with proteins
  • then periplasmic space
  • then peptidoglycan
  • then outer membrane (which contains lipopolysaccharides and proteins)
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17
Q

what is gram stain colour of gram positive in light microscopy

A

purple

- think Purple for Positive

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18
Q

what is gram stain colour of gram negative in light microscopy

A

red

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19
Q

what shape is cocci

A

spherical

- cOcci like sphere

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20
Q

what shape is bacilli

A

rod shaped

- think bacilli = baton

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21
Q

where are lipopolysaccharides present

A

in outer membrane of gram negative bacteria

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22
Q

what is fimbriae on bacteria there for

A

adherence

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23
Q

what do lipopolysaccharides do

A
  • protects peptidoglycan from bile salts
  • blocks many antibiotics from getting into cell
  • lipid A within LPS forms endotoxin which when in bloodstream may give rise to endotoxic shock (fever and low BP)
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24
Q

how do bacteria replicate

A
  • binary fission
  • asexual
  • genetic material duplicates then cell divides into two
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25
Q

how does genetic variation in bacterial cell occur

A
  • spontaneous mutation
  • transfer of plasmids between bacteria
  • conjugation is mechanism of gene transfer
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26
Q

how do you detect individual bacteria

A
  • can only be seen with microscope using stain (e.g. gram, fluorescent dyes)
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27
Q

how do you detect colonies of bacteria

A
  • cultured on solid medium (agar)

- can be seen with eye

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28
Q

what is a parasite

A

an organism that lives in or on another organism (host) and derives its nutrients at the expense of this host

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29
Q

what is a vector

A
  • intermediate host

- transmitis parasite

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30
Q

what are protozoa

A

basically single celled organisms that can live both within the environment and the host
e.g. malaria, amoebae, flagellates

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31
Q

how are protozoa transmitted

A

protozoa that live in human’s intestine - faecal-oral route (amoebae)
protozoa that live in the blood or tissue of humans - insect vector

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32
Q

what is the malaria parasite called

A

plasmodium

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33
Q

what are helminth parasites

A

worms

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34
Q

what are nematodes

A 
round worms 
(helminth)
35
Q

what are cestodes

A

tapeworms

helminth

36
Q

what are trematodes

A

flatworms/fluke

helminth

37
Q

what is enterobiasis

A

thread worm (nematode - helminth)

38
Q

what is amoebic dysentry

A

protozoa parasite

39
Q

what is route of transmission for nematodes

A

faecal-oral route

40
Q

what is ascaris lumbricoides

A

nematode (helminth)

41
Q

what is the definitive host for tapeworms

A

humans

42
Q

what is the route of transmission for tapeworms

A

eating raw/undercooked meat

43
Q

where in the body can flatworms cause infection

A

blood, lung, liver, pancreas, intestines

44
Q

what is schistosomiasis

A

trematode (helminth)

45
Q

what is the route of transmission for schistosomiasis

A

contact with fresh water where the snail (intermediate host) is present

46
Q

how to identify parasitic infection

A
  • blood microscopy e.g. malaria

- stool microscopy for enteric pathogens

47
Q

how to identify helminth infection

A

usually accompanied by eosinophilia and elevated IgE

48
Q

what does a fungus form

A

spores

49
Q

does a fungus have a cells wall

A

yes

- contains polysaccharide and it absorbs nutrients

50
Q

what are the three groups of fungi

A

basidiomycetes (e.g. mushrooms)
ascomycetes (e.g. neurospora)
zygomycetes (e.g. bread moulds)

51
Q

what is a dermatophyte’s main virulence factor

A

enzymes degrade and use keratin as a nutrient source

52
Q

what diseases are caused by dermatophytes

A

‘ringworm’ infections

- name usually starts with tinea…

53
Q

what are the main causative agents of dermatophytosis (fungal)

A
  • epidermophyton
  • microsporum
  • trichophyton
54
Q

what host factors contribute to pathogenicity of fungal infection

A
  • favourable micro-environments (warm, moist) encourage growth on skin and mucous membranes
  • broad-spectrum antibacterial agents reduce competition for colonisation sites in gut
  • immunosuppression may create a window of opportunity for fungal invasion
55
Q

what can cause immunosuppression of host defences

A

iatrogenic - steroids, chemotherapy, organ transplant

disease processes - AIDS, leukaemia, endocrinopathies

56
Q

what is yeast

A

fungus

57
Q

what is candida spp.

A

yeasts

58
Q

what does candida auris (fungus) cause

A

UTI

urinary tract infections

59
Q

what dos candida glabrata cause

A

skin infections

60
Q

what are the diagnostic methods for fungus

A

direct detection - histopathology, high-res CT scan
detection of circulating fungal antigens
detection of circulating anitbodies to fungi
PCR for fungal DNA
culture of fungus from normally sterile site
MALDI-ToF biotyping

61
Q

what are problems with anti-fungal drugs

A
  • some have narrow spectrum of activity
  • might be static (prevents multiplying) rather than cidal (kills)
  • IV vs. oral
  • toxicity
  • resistance
  • expensive
62
Q

what are some antifungals

A

echinocandins - target wall
triazoles and allylamines - target sterols
polyenes - target membrane
flucytosine - targets DNA synthesis

63
Q

what are the3

different types of structures of viruses

A

icosahedral - 20 faces, each an equilateral triangle
helical - protein binds around DNA/RNA in helical fashion
complex - neither icosahedral or helical

64
Q

where can viruses replicate

A

can only replicate within host

65
Q

what is a virion

A
  • extracellular form of virus

- exists outside host and facilitates transmission

66
Q

what is the structure of a virion

A
  • lipid envelope
  • protein capsid
  • virion associated polymerase
  • spike projections
  • nucleic acid
67
Q

how do viruses replicate

A
  1. attachment to cell
  2. uncoating of lipid envelope
  3. replication of nucleic acid (in nucleus mRNA synthesis)
  4. protein synthesis
  5. vision assembly
  6. budding and release
  7. maturation
68
Q

what are the 3 possible outcomes of viral infection

A
  • clearance of virus (with short, long term or no immunity) e.g. measles
  • chronic infection e.g. HIV, hep B
    latent infection e.g. herpes
  • transformation (long term infection with altered cellular gene expression) e.g. HPV
69
Q

what is viral latency

A
  • after infection virus lays dormant
  • full genome retained in host cell but no expression, so few viral antigens and no viral particles produced
  • reactivation can occur
70
Q

viruses and cancer examples

A

EBV: Hodgkin’s lymphoma
human herpes 8: primary effusion lymphoma
human T cell lymphotropic virus (HTLV) leukaemia
HPV: cervical, anal cancers
hep B/C: hepatocellular carcinoma

71
Q

what are the viral detection methods for the whole organism

A
  • microscopy

- culture

72
Q

what would be the viral detection methods for part of the organism

A
  • antigen detection
  • DNA/RNA detection (extraction of genetic material from sample)
  • PCR
73
Q

what would be the viral detection methods for immune response

A
  • antibody detection (serology)
74
Q

are antiviral therapies virustatic or virucidal

A

all are virustatic

75
Q

what are antiviral therapies used for

A

prophylaxis - to prevent infection

pre-emptive therapy - when evidence of infection/replication detected but before symptoms are apparent

overt disease

suppressive therapy - to keep replication low

76
Q

viruses with what properties can be eradicated

A
  • no animal reservoir or ability to amplify in environment
  • clearly identifiable
  • no chronic carrier state
  • efficient and practical intervention e.g. vaccine
  • political/social support
    e. g. measles, polio
77
Q

what are some signs of clinical infection

A

inflammation, pain, pyrexia (fever), tachycardia (fast heart rate), rigors (temperature rises and shivers), increased white cell count, increased reactive protein (CRP)

78
Q

what is a commensal

A

an organism which is part of normal flora

79
Q

what is infectivity

A

ability to become established on or within a host

80
Q

what are exotoxins

A

released extracellularly by the micro-organism

81
Q

what are enterotoxins

A

exotoxins which act on the GI tract

82
Q

what are endotoxins

A

structurally part of the gram negative cell wall

83
Q

what are superantigens

A

certain exotoxins of strep progenies and staph aureus

  • able to stimulate division of T cells in the absence of specific antigen
  • overwhelming cytokine production causes ‘toxic shock’

principles of disease (19 decks)

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