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Flashcards in Medical Microbiology Deck (109):
1

What are psychrophiles

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

2

How many chromosomes do prokaryotes have?

1

3

What type of ribosomes do prokaryotes have?

70s

4

What type of ribosomes do eukaryotes have?

80s

5

How big are prokaryote cells?

1 - 10 um

6

How big are eukaryote cells?

10 - 100 um

7

What are the 6 shapes of bacteria?

Coccus
Bacillus
Spirochete
Spirilium
Coccobacillus
Vibrio

8

Give an example of a coccus bacteria?

Streptococcus

9

Give an example of a vibrio bacteria

Vibrio cholerae

10

Give an example of a bacillus bacteria?

P aeruginosa

11

Give an example of a coccobacillus?

Chlamydia

12

What are the three growth types for cocci?

Chain
Packet
Cluster

13

What are the 4 components used in the gram stain?

Crystal violet primary stain
Iodine mordant
Alcohol decolouriser
Safarin counterstain

14

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

Crystal violet dye - stains all cells purple

15

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

Iodine. It forms insoluble complexes with the crystal violet dye

16

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

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

17

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

Safarin. It stains both cell types pink

18

What does the peptidoglycan layer contain in gram positive cells?

Teichoic acids and lipteichoic acids

19

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

To hide from the immune system

20

What does the outer membrane of gram negative bacteria contain?

Porins and endotoxin. Endotoxin activates the innate immune system.

21

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

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

22

What is peptidoglycan made up of?

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

23

Which enzymes are involved in peptidoglycan synthesis?

Transglycosylases which connect sugars and transpeptidases which form peptide crosslinks

24

How do beta lactams inhibit cell wall synthesis?

Inhibit transpeptidase reaction

25

How does vancomycin inhibit cell wall synthesis?

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

26

What is the glycocalyx? Give examples

Generic name for extracellular polymers. Capsule and slime layer

27

What is the capsule used for?

Biofilm production

28

What is the slime layer used for?

Movement

29

What are 3 types of pili?

Fimbriae
Type 4 pili
Sex pili

30

What are fimbriae?

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

31

What are type 4 pili used for?

Movement

32

How do cells move?

Runs and tumbles

33

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

Tumbles are less frequent. Runs are longer.

34

Which type of bacteria form endospores and in what situation?

Gram positive bacteria form endospores when nutrients run out

35

What are the 4 arrangements of flagella?

Monotichous
Lophotrichous
Amphitrichous
Petritrichous

36

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

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

37

What are the 3 growth types for cocci?

Chain
Packet
Cluster

38

Halophile

Requires salt to grow

39

Halotolerant

Can grow in mild salt concentrations but grow best without salt

40

Osmophiles

Can survive in high sugar environments

41

Xerophiles

Can survive in dry environments (usually fungi)

42

Neutrophile

Grows best between pH 5.4 and 8.5

43

Psychotrophs

Optimum is around room temperature but can grow in the fridge

44

Mesophiles

Optimum between 20 and 40 degrees (all animal pathogens)

45

Thermophiles

Optimum 50 to 80 degrees

46

Obligate aerobe

Has SOD and catalase
Requires oxygen

47

Facultative anaerobe

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

48

Aerotolerant anaerobe

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

49

Strict anaerobe

Has neither SOD nor catalase
Some tolerate oxygen, some killed by it

50

Microaerophile

Has SOD and some have catalase
Grows best in low oxygen conditions

51

Aerobe

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

52

Can aerobes carry out fermentation?

No

53

What charge does a biofilm matrix have?

Negative

54

What are persister cells?

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

55

Why is natural flora important?

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

56

Factors determining microbiome

Host physiology
Host pathobiology
Immune system
Lifestyle
Genotype
Environment

57

How is flora on the skin limited?

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

58

What is the microbiome of the oropharynx?

HACEK organisms
(Like elevated CO2 and are slow growing)

59

How are microbes removed from the respiratory tract?

Lysozyme
Macrophages
Mucus
Ciliated cells

60

What does the the colon microbiome secrete?

Vitamin k and B

61

What are antimicrobial secretions?

Lysozymes
Lactoferrin
Cathelicidin
Defensins

62

What is found in granules of NK cells?

Perforin and granzyme

63

ID50

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

64

How do pathogens attach to host cells?

Fimbriae
Capsule

65

How do microbes cross the mucosa?

The use M cells

66

Name the 4 classes of s aureus virulence factors

Adhesins
Invasins
Siderophores
Haemolysins

67

Name the 2 invasins in s aureus

Staphylokinase
Hyaluronidase

68

What does staphylokinase do?

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

69

What does hyaluronidase do?

Lyses hyaluronic acid found in connective tissue which causes tissue breakdown

70

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

Coagulase
Staphyloxanthin
S aureus protein A

71

What does coagulase do?

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

72

What does staphyloxanthin do?

Antioxidant that protects against ROS

73

What does s aureus protein do?

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

74

What is PVL?

S aureus toxin which is cytotoxic to WBC

75

Name 3 s aureus toxins

Pyrogenic
Exfoliating
Membrane damaging

76

What does pyrogenic toxin cause?

Toxic shock syndrome

77

How does superantigen cause toxic shock syndrome?

More T cells activated so more cytokines activated

78

What does exfoliating toxin do?

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

79

Infectivity

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

80

Secondary attack rate

Rates of infection among individuals exposed to a first case

81

Pathogenicity

Measure of disease causing propensity (ID50)

82

Virulence

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

83

Incubation period

Time between exposure and onset of symptoms

84

What are the 5 Is?

Inoculation
Isolation
Incubation
Inspection
Identification

85

Chocolate agar

Blood heated to release nutrients

86

Name the 5 selective media

Phenylethyl alcohol
Blood
Macconkeys
EMB
Baird parker

87

Phenylethyl alcohol agar

Selects out gram negatives by reversibly inhibiting their dna synthesis

88

Baird parker agar

Selects staphylococci
Contains egg yolk

89

EMB media

Lactose fermenting - metal sheen
Non lactose fermenting - colourless

90

MacConkeys

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

Lactose fermenting - produces acid so indicator turns red

Non lactose fermenting - colourless

91

Capnophile

Likes elevated CO2 conc

92

Alpha haemolysis

Lots of haemolysis

93

Beta haemolysis

Some haemolysis
Green halo

94

What are 6 biochemical tests?

Catalase
Oxidase
Indole
Urease
Coagulase
Carbohydrate fermenting

95

Oxidase test

Cytochrome c oxidase (purple when positive)

96

Indole test

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

97

Urease test

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

98

Coagulase test

Mix with plasma, look for clot

99

Carbohydrate fermentation

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

100

What are the cons of traditional methods?

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

Slow growing

Poor discrimination between similar microbes

101

What immunological methods are used?

Agglutination
Immunofluorescence
ELISA
Immunodiffusion assays

102

Direct immunofluorescence

Antigen from patient
Fluorescent antigen from lab

103

Indirect immunofluorescence

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

104

What are the molecular methods used?

PCR and real time PCR
Nucleic acid probes
RFLP
Plasmid fingerprinting

105

What are the 4 different types of CD4 T cells?

Th1
Th2
Th17
TFH

106

What is the role of Th1 cells?

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

107

What is the role of Th2 response?

Deals with infections at mucosal surfaces, parasite infections and allergies

108

Th17 response

Deals with extracellular bacteria and fungi

109

TFH response

Helps B cells produce antibody