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Stage 2 Cheat sheets > MFD > Flashcards

MFD Flashcards

1
Q

Purpose of Koch’s postulates?

A

Scientific approach to finding the cause of infections

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2
Q

Koch’s Postulates

A
  1. Organism must be present in every case of disease and not present in health
  2. Organism must be isolated in pure culture
  3. Isolated organism must cause disease in suitable animal
  4. Organism must be re-isolated from infected animal
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3
Q

When is Koch’s postulates not possible to fulfil (relating to each step)?

A
  1. Asymptomatic carriers e.g. cholera
  2. Viruses could not be cultured in 1900s and prions are still hard to culture. Some infections are poly microbial
  3. Suitable animal may not be available and may not be representative of humans
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4
Q

Koch’s postulate cannot be applied when: (5)

A

No infecting species detected
Bacteria cannot be grown in culture
No suitable animal model available
More than one species of bacterium involved
The level of species rather than the presence of the species is important

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5
Q

How has Koch’s postulates changed in molecular biology era?
Positives

How has this development changed views on what infectious disease are?

A

DNA analysis is often used to determine the infectious species (PCR, hybridisation, sequencing)

  • this circumvents need for isolation
  • very sensitive and often detects even in absence of disease
  • may be quantitative (can tell you how much there is)

Infectious disease now regarded as imbalances in microbiota

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6
Q

What is latex agglutination used for?

A

Antigen detection

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7
Q

How does latex agglutination work?

A

Latex article is coated in antibodies specific for the capsular polysaccharide antigen of the bacterium, this causes agglutination of the sample (positive result)

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8
Q

Why is latex agglutination better than growing on carbohydrate agar?

A

It is quicker and cheaper (don’t need to wait for it to grow) and very specific
Can be useful if patient has received antibiotic treatment so the organisms appear morphologically unidentifiably in sample and may not grow in culture

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9
Q

What type of antigen is latex agglutination used to detect?

A

Legionella in urne

Streptococcus Pneumoniae in CSF

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10
Q

Advantages of latex agglutination?

A

Quick
Cheap
Specific

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11
Q

What is critical pH of mouth?

A

Approx 5.5

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12
Q

why do people have different critical pH?

A

Critical pH dependent on calcium and phosphate concentration in saliva which is dependent on individuals saliva flow rate, this differs dramatically

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13
Q

Name the 3 plaque hypothesis?

A

Specific plaque hypothesis
Non-specific plaque hypothesis
Ecological plaque hypothesis

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14
Q

Specific plaque hypothesis

A

Disease caused by single microorganism

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15
Q

Non-specific plaque hypothesis

A

Disease caused by amount of plaque present

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16
Q

Ecological plaque hypothesis

A

Disease caused by interactions of specific micro-organisms with the microbial community

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17
Q

Normal pH of the mouth?

A

Approximately 6.2-7.5

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18
Q

What happens if HA left in pH7?

Why does the temperature rise?

A

HA normally lives at pH 6.5
Increase in pH will shift equilibrium to the left and increase bond making
Exothermic reaction = increase in temperature

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19
Q

Function of peptidoglycan?

A

Forms cell wall of bacteria
Provides structure and resists osmotic effects of cytoplasm
Involved in binary fission

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20
Q

Opportunistic pathogen

A

Pathogen that grows in an environment not normally available in the host e.g. weakened immune system

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21
Q

What agents aren’t killed by sterilisation?

A

Prions

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22
Q

How does antibiotic resistance occur?

A

Bacteria in human body, some are more resistant than others
Antibiotics kills the susceptible strain and the resistant strains live
Resistant strains replicate
Resistance spreads

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23
Q

Intrinsic resistance

A

Innate property of bacterium seen in all strains e.g. G-ve to beta lactic ring

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24
Q

Acquired resistance

A

Resistance selected by antibiotic use e.g penicillin and staph aureus

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25
Q

Cross resistance

A

Resistance to one AB leads to resistance to another (in the same class)

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26
Q

Multi-resistance

A

Resistance to several AB via independent mechanisms

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27
Q

Why is vancomycin and neomycin used int he agar to select for fusobacterium?

A

Fusobacterium have innate resistance to vancomycin and neomycin
Vanco = too large to cross the G-ve outer membrane
Neo = needs an active election transport chain for uptake, anaerobic bacteria do not have these

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28
Q

How is resistance transferred?

A

Mutation
Tranformation
Transduction
Conjugation

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29
Q

Transformation?

A

Cell lysis
DNA into environment
Taken up into bacteria and incorporated into their DNA

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30
Q

Transduction?

A

Viruses infect bacteria cell, incorporate parts of DNA into their genome, kill cell and spread

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31
Q

Conjugation?

A

Pili

Donor cell contains plasmid and pili, makes contact with host and transfers

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32
Q

Main mechanism of resistance (3)

A

Modification of AB
Modification of target
Preventing drug reaching target

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33
Q

Mode of action of penicillin

A

Inhibit transpeptidase forming cross linked in peptidoglycan cell wall (between NAM and NAG as glycine)
Bacteria swell and rupture

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34
Q

Why is amoxicillin better than penicillin?

A

Wider range of action
Effective against G-ve as it contains amino group to penetrate outer membrane
Longer duration of action

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35
Q

Mechanism of action for sulphonamides?

A

act as a false substrate for dihydropterate synthetase in folate synthesis

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36
Q

How are sulphonamides selective to bacteria?

A

Bacteria have to make own folate = intracellular

Humans get it from diet

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37
Q

Nature of sulphonamides?

a) Bacteriocidal
b) Bacteriostatic
c) Bacteriolytic

A

B Bacteriostatic

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38
Q

Mode of action of flouroquiolones?

A

Inhibit DNA gyrase in G-ve and DNA topioisomerase in G+ve

stop DNA replication

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39
Q

Mode of action for macrolides

A

Block protein synthesis by blocking translocation on large ribosomal subunit

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40
Q

Mode of action for tetracylines

A 
Small subunit
Block elongation (join gin of AA)
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41
Q

Structural features of archaea

A

Prokaryote

No nucleus, single celled, no internal organelles, coiled ring of DNA

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42
Q

How to take sample of archaea organisms from mouth?

A

Anaerobes so sub-gingival swab

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43
Q

Difference between specificity and sensitivity?

A 
Specificity = proportion of people who test negative and remain disease free
Sensitivity = proportion of people who test positive and develop disease
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44
Q 
Calculating specificity and sensitivity from table
                         Disease
                 Yes             No
        \+ve    a                 b 
Test
         -ve    c                 d
A 
Sensitivity = a/a+c
Specificity = d/d+b
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45
Q

2 molecular components contributing to fighting fungal infections

A

Azoles

Polyenes

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46
Q

How can dental clinicians avoid spread of antibiotic resistance?

A

Follow up to date prescription guidance
Don’t give as a preventative measure
Prioritise local measures
Inform patient on options, risks and risks on over prescribing

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47
Q

Why is saliva hypotonic?

A

Resorption of Na+ and Cl- is greater than secretion of K+ and HCO3- in salivary duct
Duct cells are impermeable to water so water stays within the lumen reducing the concentration of the solute in the saliva

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48
Q

Why do B lactase only work on growing bacteria?

A

Transpeptidase is not active in quiescent bacteria

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49
Q

Function of MacConkey agar

Positive test, Negative test

A

Differentiate between bacteria that can ferment lactose and those that cannot
Select for G-ve enterobacteria using bile salts
If fermenting lactose = produces acid = pH indicator turns red
If fermenting proteins = produce alkali substance = pH indicator = yellow

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50
Q

Why does number of CFU not equal total number of bacteria?

A

Some cells may be dead/non-vaibale/unable to grow on particular medium
Some cells clump together or form chains = may appear as one CFU

51
Q

3 red complex bacteria?

A

P. gingivalis
T. denticola
T. forsythia

52
Q

Orange complex bacteria?

A

Fusobacterium

53
Q

Obligate anaerobes

Environment?

A

Unable to live in areas where there is oxygen

Subgingivally

54
Q

2 bacteria in Mutans Streptococci?

A

Strep. Mutans

Strep. Sobrinus

55
Q

Example of bacteria that does beta haemolysis?

Appearance on agar?

A

Streptococcus pyogenes

Transclucent

56
Q

Example of bacteria that does alpha haemolysis?

Appearance on agar?

A

Streptococcus Gordonii

Red with greenish tinge

57
Q

Example of bacteria that does gamma haemolysis?

Appearance on agar?

A

Staphylococcus epidermis

No haemolysis = red

58
Q

4 labels on batch curve of bacteria?

A 
Lag = slow growth because small number of bacteria
Exponential = growth increases quickly
Stationary = growth = death = limited availability of nutrients
Death = too many bacteria and absence of nutrients = reduction
59
Q

2 compounds causing halitosis?

A

Volatile sulphur compounds e.g. hydrogen sulphide

Protein and amino acid metabolites e.g. skatole/cadaverine

60
Q

What is a plasmid?

A

Small circular string of DA in cytoplasm, containing useful but not essential genes for survival

61
Q

Endotoxin

A

Bacterial virulence factor = LPS = associated with cell wall of G-ve
When cell dies Lipid A from LPS = pro-inflammatory

62
Q

Definition of neurotoxin

A

Exotoxin that destroys nervous tissue

63
Q

2 types of exotoxins secreted by bacteria?

A

Tetanus toxin and botulinum

64
Q

Faculatative anaerobe

A

Can use oxygen to make ATP but when oxygen is not present can switch to fermentation

65
Q

How do Mutans polymers support plaque?

A

Increase adhesion and survival of mutant streptococci

66
Q

What is the Snyder test used to determine?

A

Susceptibility to caries - selects acidogenic bacteria e.g. lactobacilli

67
Q

Which carbohydrate is fermented in Snyder test?

A

Glucose

68
Q

How does fluoride affect critical pH?

A

Reduce so the environment can be more acidic before dissolution

69
Q

Main virulence factor of Aa?

A 
Leukotoxin
LPS
adhesions (fimbriae)
Cytolethal distending toxin
Proteases
70
Q

FAA agar?

Identifies?

A

Fastisious anaerobe agar?

Non-selective anaerobes

71
Q

How can FAA be made selective fro fusobacterium?

A

Add vancomycin and neomycin = resistant to both of these (too large and doesn’t have the transporter)

72
Q

Blood agar?

Identifies?

A

Nutrient-rich, non-selective

73
Q

TYCS agar?

Identifies?

A

Tryptone Yeats Cysteine
S. mutans and other streptococci by having high sucrose levels = glucans
Distinguished between S. mutans and S. sanguinis

74
Q

MSB agar?

Identifies?

A

Mitis Salivarius Bacitracin

Distinguish between S. Mitis and S> salivarius

75
Q

What enzyme tests distinguish

a) E.coli
b) S. aureus
c) S. salivarius

A

a) -ve urease, +ve catalase, -ve DNAase
b) -ve urease, +ve catalase, +ve DNAase, +ve coagulase
c) +urease, -ve catalase, -ve DNAse

76
Q

Virulence factors of

a) T. Forsythia
b) T. denticola
c) P. gingivalis
d) S, aureus
e) Aa
f) C. albicans

A

a) Glycosylated S layer to hide from immune cells
b) Flagellum and majro sheath protein
c) proteases, LPS
d) Exotoxins
e) leukotoxin
f) hyphae formation and phenotypic switching

77
Q

On blood agar what will appear red when looking at it? Bacteria?

A

Due to alpha haemolysis = S. Gordonii

78
Q

Which antibiotic causes fluorescence?

A

Tetracycline

79
Q

What is calculus?

A

Plaque depositions that irritate the human and cause inflammation

80
Q

What is added to toothpastes to reduce calculus formation?

A

Anti-bacterial agents

81
Q

MIC

MBC

A

Minimum inhibitory concentration

Minimum bactericidal concentration

82
Q

Sections of LPS

A

Lipid A = inflammatory response

O antigen

83
Q

What bacteria brows on NaCl agar?

A

Staphyloccus

84
Q

How is cholera transmitted?

A

Food or water that have been contaminated with faeces from contaminated person

85
Q

What do you clean clinical surfaces with?

A

Disinfectant

86
Q

What would you clean a blood spillage with?

A

Wipe area with water and detergent until visibly clean and the use sodium hypochlorite (bleach)

87
Q

What produce black colonies on blood agar?

A

P. gingivalis due to porphoryn pigments containing heam

88
Q

Main etiological factor of caries

A

Microbial dysbiosis, bacterial fermentation

89
Q

2 main spore forming bacteria

A

Bacillus anthracsis, Clostridium difficile

90
Q

What component of enamel pellicle functions by stabilising calcium and phosphates with oral environment?

A

Proline rich proteins

Slatherin

91
Q

What inhibits growth by binging enzyme co-factor?

A

Lactoferrin

92
Q

When sugar in low quantities, what is a virulence factor of mutans?

A

Antigen I and II can bind lots of structures with high affinty

93
Q

Action of antigen I/II on streptococci?

A

Mediate adhesion in pellicle and binds bacteria e.g. p. gingivalis and Aa

94
Q

What is chlorhexidine?

A

Disinfectant and antiseptic used for disinfection fo skin and surfaces

95
Q

What is autoclaving unable to kill?

A

Prions

96
Q

What procedure is used to treat a dental hand piece?

A

Steralisation through autoclaving (heat and pressure)

97
Q

Prion

A

Misfolded proteins which form aggregates = highly resistant

98
Q

What salivary element is a potent inhibitor of candida albicans?

A

Competence stimulating protein of S. mutans inhibit hype formation
Lactobacillus

99
Q

What component of s. gordonii promotes binding to Candida albicans hyphae form?

A

Antigen I/II

100
Q

What contributes to pathogenicity of Staph Aureus?

A

Exotoxin production

Results in toxic shock syndrome

101
Q

What bacterial component causes an acute inflammatory response?

A

LPS (G-ve)

102
Q

What is CLED agar?

A

Cysteine, lactose, electrolyte deficienent agar

103
Q

Why is CLED used to culture urinary microbes?

A

Cysteine and lactose promote the growth of the pathogens but lack of electrolytes prevents the swarming of proteus species

104
Q

What are the selective agents of MacConkey agar? How do they work?

A

Bile salts and crystal violet iodine stain
Inhibits growth of Gram +ve
Selects for gram -ve
Because G-ve have outer membrane which decreases the permeability to bile salts - bile salts can’t cause protein aggregation

105
Q

What is the product of tryptophan metabolism? Consequence?

A

Skatole

Halitosis

106
Q

2 products of protein breakdown and the consequence?

A

Cadervine, Putrescine

Halitosis

107
Q

What is BANA test used for?

A

Halitosis diagnosis by detecting presence of periodontal pathogens

108
Q

What bacteria will test positive in a BANA test?

A

Red complex bacteria
P. gingivalis
T. denticola
T. forsythia

109
Q

Which bacteria is a spirochete?

A

T. denticola

110
Q

Units of Ksp (solubility product?

A 
(Moles/L) to the power of the number of products e.g.
HA
10 Ca
6 PO3
2 OH
(moles/L)18
111
Q

3 most outer layers of bacteria?

A

Capsule
Cell wall
Plasma membrane

112
Q

Function of capsule

A

Protect against phagocytosis

113
Q

Function of cell inclusion bodies?

A

Nutrient reserve and protect against osmotic shock

114
Q

Function of Fimbriae
Function of Flagellae
Structural difference

A

Fimbriae = adhesion of biofilm
Flagellae = motility
Fimbriae are much smaller and in higher numbers

115
Q

Microorganism responsible for stomach ulcers

A

Helicobacter pilori

116
Q

Microorganism responsible for chicken pox?

A

Varicella zoster virus (type of herpes)

117
Q

Microorganism responsible for cold sores?

A

Herpes simplex

118
Q

Genetic structure of

a) Herpes
b) HIV

A

a) Double stranded DNA

b) Single stranded RNA

119
Q

What is a retrovirus?

Example?

A

An RNA virus that inserts its DNA into the host cell changing the genome of that cell
HIV

120
Q

What 2 substances act as a buffer?

A

Saliva and GCF

121
Q

What and how does staphylococcal agar select for?

A

Staphyloccus bacteria = high salt content

122
Q

How does candida agar select for candida?

A

Low pH
Chloramphenicol which inhibits bacterial growth
Chromogenic substances that are cleaved by certain enzymes in the candida = different colours

123
Q

Why does S. Aureus appear gold?

A

Contains staphyloxanthin

124
Q

What makes some E coli pathogenic?

A

Possession of O antigen 157 or H antigen 7

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