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Biomedical Sciences > Medical Microbiology > Flashcards

Medical Microbiology Flashcards

1
Q

What are psychrophiles

A

Microorganisms that can grow in extremely cold temperatures (-20)

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2
Q

How many chromosomes do prokaryotes have?

A

1

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3
Q

What type of ribosomes do prokaryotes have?

A

70s

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4
Q

What type of ribosomes do eukaryotes have?

A

80s

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5
Q

How big are prokaryote cells?

A

1 - 10 um

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6
Q

How big are eukaryote cells?

A

10 - 100 um

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7
Q

What are the 6 shapes of bacteria?

A 
Coccus
Bacillus
Spirochete
Spirilium
Coccobacillus
Vibrio
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8
Q

Give an example of a coccus bacteria?

A

Streptococcus

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9
Q

Give an example of a vibrio bacteria

A

Vibrio cholerae

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10
Q

Give an example of a bacillus bacteria?

A

P aeruginosa

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11
Q

Give an example of a coccobacillus?

A

Chlamydia

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12
Q

What are the three growth types for cocci?

A

Chain
Packet
Cluster

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13
Q

What are the 4 components used in the gram stain?

A

Crystal violet primary stain
Iodine mordant
Alcohol decolouriser
Safarin counterstain

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14
Q

What is the primary stain in gram staining and what does it do?

A

Crystal violet dye - stains all cells purple

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15
Q

What is the mordant used in gram staining and what does it do?

A

Iodine. It forms insoluble complexes with the crystal violet dye

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16
Q

What is the decolouriser used in gram staining and what does it do?

A

Removes crystal violet iodine complexes from gram negative but not gram positive

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17
Q

What is the counterstain used in gram staining and what does it do?

A

Safarin. It stains both cell types pink

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18
Q

What does the peptidoglycan layer contain in gram positive cells?

A

Teichoic acids and lipteichoic acids

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19
Q

What is the role of the s layer in bacterial cells?

A

To hide from the immune system

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20
Q

What does the outer membrane of gram negative bacteria contain?

A

Porins and endotoxin. Endotoxin activates the innate immune system.

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21
Q

Where is the s layer found on gram postive and gram negative bacterial cells?

A

Peptidoglycan layer of gram positives. Outer membrane of gram negatives.

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22
Q

What is peptidoglycan made up of?

A

Repeating structure of 2 alternating sugars (nam and nag) crosslinked by peptides

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23
Q

Which enzymes are involved in peptidoglycan synthesis?

A

Transglycosylases which connect sugars and transpeptidases which form peptide crosslinks

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24
Q

How do beta lactams inhibit cell wall synthesis?

A

Inhibit transpeptidase reaction

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25
Q

How does vancomycin inhibit cell wall synthesis?

A

Binds to d-ala-d-ala to stop cross linking

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26
Q

What is the glycocalyx? Give examples

A

Generic name for extracellular polymers. Capsule and slime layer

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27
Q

What is the capsule used for?

A

Biofilm production

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28
Q

What is the slime layer used for?

A

Movement

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29
Q

What are 3 types of pili?

A

Fimbriae
Type 4 pili
Sex pili

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30
Q

What are fimbriae?

A

Short pili which are used to attach bacteria to surfaces. They are made up of helically arranged proteins tipped with adhesive proteins.

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31
Q

What are type 4 pili used for?

A

Movement

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32
Q

How do cells move?

A

Runs and tumbles

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33
Q

When a cell is near an attractant, how do its runs and tumbles change?

A

Tumbles are less frequent. Runs are longer.

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34
Q

Which type of bacteria form endospores and in what situation?

A

Gram positive bacteria form endospores when nutrients run out

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35
Q

What are the 4 arrangements of flagella?

A

Monotichous
Lophotrichous
Amphitrichous
Petritrichous

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36
Q

What are the 6 shapes of bacterial cells, give examples of each

A 
Coccus (streptococci)
Bacillus (p aeruginosa)
Coccobacillus (chlamydia)
Vibrio (vibrio cholerae)
Spirilium
Spirochete
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37
Q

What are the 3 growth types for cocci?

A

Chain
Packet
Cluster

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38
Q

Halophile

A

Requires salt to grow

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39
Q

Halotolerant

A

Can grow in mild salt concentrations but grow best without salt

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40
Q

Osmophiles

A

Can survive in high sugar environments

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41
Q

Xerophiles

A

Can survive in dry environments (usually fungi)

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42
Q

Neutrophile

A

Grows best between pH 5.4 and 8.5

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43
Q

Psychotrophs

A

Optimum is around room temperature but can grow in the fridge

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44
Q

Mesophiles

A

Optimum between 20 and 40 degrees (all animal pathogens)

45
Q

Thermophiles

A

Optimum 50 to 80 degrees

46
Q

Obligate aerobe

A

Has SOD and catalase

Requires oxygen

47
Q

Facultative anaerobe

A

Has SOD and catalase
Does not require oxygen but grows best when oxygen is available
S aureus
Fermentation when oxygen is unavailable

48
Q

Aerotolerant anaerobe

A

Has SOD but not catalase
Grows equally well with or without oxygen
Streptococcus pyogenes

49
Q

Strict anaerobe

A

Has neither SOD nor catalase

Some tolerate oxygen, some killed by it

50
Q

Microaerophile

A

Has SOD and some have catalase

Grows best in low oxygen conditions

51
Q

Aerobe

A

An organism which uses oxygen as the terminal electron acceptor in a respiratory chain

52
Q

Can aerobes carry out fermentation?

A

No

53
Q

What charge does a biofilm matrix have?

A

Negative

54
Q

What are persister cells?

A

They are found in biofilms. They neither grow nor die in the presence of antimicrobials. They are multi drug tolerant (MDT)

55
Q

Why is natural flora important?

A

Prevents growth of pathogenic flora by competition and amensalism (secretion of inhibitory substances)

56
Q

Factors determining microbiome

A 
Host physiology
Host pathobiology
Immune system
Lifestyle
Genotype
Environment
57
Q

How is flora on the skin limited?

A

Dessication
Lack of nutrients
Disinfectant secretions (lysozyme which cleaves peptidoglycan and cathelicidin which forms pores)

58
Q

What is the microbiome of the oropharynx?

A

HACEK organisms

Like elevated CO2 and are slow growing

59
Q

How are microbes removed from the respiratory tract?

A

Lysozyme
Macrophages
Mucus
Ciliated cells

60
Q

What does the the colon microbiome secrete?

A

Vitamin k and B

61
Q

What are antimicrobial secretions?

A

Lysozymes
Lactoferrin
Cathelicidin
Defensins

62
Q

What is found in granules of NK cells?

A

Perforin and granzyme

63
Q

ID50

A

Infectious dose 50. Number of cells that results in disease for 50% of population

64
Q

How do pathogens attach to host cells?

A

Fimbriae

Capsule

65
Q

How do microbes cross the mucosa?

A

The use M cells

66
Q

Name the 4 classes of s aureus virulence factors

A

Adhesins
Invasins
Siderophores
Haemolysins

67
Q

Name the 2 invasins in s aureus

A

Staphylokinase

Hyaluronidase

68
Q

What does staphylokinase do?

A

Cleaves plasminogen to plasmin which degrades fibrin clots. Cleaves IgG. Cleaves C3b which inhibits phagocytosis

69
Q

What does hyaluronidase do?

A

Lyses hyaluronic acid found in connective tissue which causes tissue breakdown

70
Q

What 3 substances does s aureus use to evade the immune system?

A

Coagulase
Staphyloxanthin
S aureus protein A

71
Q

What does coagulase do?

A

Reacts with thrombin forming staphylothrombin which cleaves fibrinogen to fibrin. S aureus coated with fibrin can evade the immune system

72
Q

What does staphyloxanthin do?

A

Antioxidant that protects against ROS

73
Q

What does s aureus protein do?

A

Binds to Fc portion of IgG and prevents phagocytosis by preventing opsonisation

74
Q

What is PVL?

A

S aureus toxin which is cytotoxic to WBC

75
Q

Name 3 s aureus toxins

A

Pyrogenic
Exfoliating
Membrane damaging

76
Q

What does pyrogenic toxin cause?

A

Toxic shock syndrome

77
Q

How does superantigen cause toxic shock syndrome?

A

More T cells activated so more cytokines activated

78
Q

What does exfoliating toxin do?

A

Cleaves cadherin which forms junctions between skin cells. Leads to skin peeling

79
Q

Infectivity

A

Propensity for transmission. Measured by secondary attack rate in a household

80
Q

Secondary attack rate

A

Rates of infection among individuals exposed to a first case

81
Q

Pathogenicity

A

Measure of disease causing propensity (ID50)

82
Q

Virulence

A

Propensity to cause severe disease. Measured by fatality ratio or LD50

83
Q

Incubation period

A

Time between exposure and onset of symptoms

84
Q

What are the 5 Is?

A 
Inoculation
Isolation
Incubation
Inspection
Identification
85
Q

Chocolate agar

A

Blood heated to release nutrients

86
Q

Name the 5 selective media

A 
Phenylethyl alcohol
Blood
Macconkeys
EMB
Baird parker
87
Q

Phenylethyl alcohol agar

A

Selects out gram negatives by reversibly inhibiting their dna synthesis

88
Q

Baird parker agar

A

Selects staphylococci

Contains egg yolk

89
Q

EMB media

A

Lactose fermenting - metal sheen

Non lactose fermenting - colourless

90
Q

MacConkeys

A

Selects gram negatives (bile salts inhibit growth of gram positives)

Lactose fermenting - produces acid so indicator turns red

Non lactose fermenting - colourless

91
Q

Capnophile

A

Likes elevated CO2 conc

92
Q

Alpha haemolysis

A

Lots of haemolysis

93
Q

Beta haemolysis

A

Some haemolysis

Green halo

94
Q

What are 6 biochemical tests?

A 
Catalase
Oxidase
Indole
Urease
Coagulase
Carbohydrate fermenting
95
Q

Oxidase test

A

Cytochrome c oxidase (purple when positive)

96
Q

Indole test

A

Tests for tryptophanase which turns tryptophan into pyruvate, indole and urea. DMAB turns red when indole present

97
Q

Urease test

A

Urease hydrolyses urea to ammonia which increases pH. Indicator turns pink

98
Q

Coagulase test

A

Mix with plasma, look for clot

99
Q

Carbohydrate fermentation

A

Positive - acid or gas production
Acid turns indicator yellow
Gas in collected in upturned durham tube

100
Q

What are the cons of traditional methods?

A

Organism must be able to be cultured in vitro (obligate intracellular cannot)

Slow growing

Poor discrimination between similar microbes

101
Q

What immunological methods are used?

A

Agglutination
Immunofluorescence
ELISA
Immunodiffusion assays

102
Q

Direct immunofluorescence

A

Antigen from patient

Fluorescent antigen from lab

103
Q

Indirect immunofluorescence

A

Antigen from lab mixed with patient serum. Antibody against patient antibody fluoresces

104
Q

What are the molecular methods used?

A

PCR and real time PCR
Nucleic acid probes
RFLP
Plasmid fingerprinting

105
Q

What are the 4 different types of CD4 T cells?

A

Th1
Th2
Th17
TFH

106
Q

What is the role of Th1 cells?

A

They recognise mycobacteria derived antigens on macrophages and secrete cytokines which help overcome lysosome binding

107
Q

What is the role of Th2 response?

A

Deals with infections at mucosal surfaces, parasite infections and allergies

108
Q

Th17 response

A

Deals with extracellular bacteria and fungi

109
Q

TFH response

A

Helps B cells produce antibody

Biomedical Sciences (6 decks)

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