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My Phase 2a > MY Microbiology > Flashcards

MY Microbiology Flashcards

1
Q

Define a pathogen

A

An organism that causes or is capable of causing disease

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2
Q

Define commensal

A

An organism that colonises the host but no disease is caused in normal circumstances

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3
Q

Define an opportunist pathogen

A

A pathogen that only causes disease if the host’s defences are compromised

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4
Q

Virulence =

A

The degree to which an organism is pathogenic

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5
Q

What is asymptomatic carriage

A

Where a pathogen is carried harmlessly at a tissue site where it does NOT cause disease

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6
Q

T/F
Viruses are larger than bacteria

A

False

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7
Q

T/F
Viruses can be viewed on a microscope

A

False

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8
Q

What areas of the body are sterile
What happens if bacteriaa enters these organs

A
  • lungs
  • blood
  • kidneys
  • gall bladder
  • an immune response is raised if bacteria enters these organs
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9
Q

What colour does gram negative bacteria stain

A

Pink

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10
Q

What colour does gram positive bacteria stain

A

Purple

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11
Q

Describe the 2 main basic bacterial morphology

A

Coccus - round
Bacillus - rod

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12
Q

Diplococcus =

A

Pair of cocci

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13
Q

Streptococcus =

A

Chain of cocci

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14
Q

Staphylococcus =

A

Cluster of cocci =

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15
Q

Vibrio =

A

Curved rod

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16
Q

Spirochaete =

A

Spiral rod
- classified separately to rods

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17
Q

6 basic components of a bacterial cell

A
  1. Cell wall
  2. Inner membrane
  3. Outer membrane
  4. Chromosome of Circular double stranded DNA
  5. Pili
  6. Capsule
    5+6 not always present
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18
Q

Components of gram +ve bacterial cell envelope

A
  • capsule
  • peptidoglycan
  • cytoplasmic membrane
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19
Q

Components of gram -ve bacterial cell envelope

A
  • capsule
  • lipopolysacharide ( endotoxin)
  • outer membrane
  • peptidoglycan
  • inner membrane
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20
Q

Which has a thicker peptidoglycan layer - gram +ve or -ve

A

Positive
P for peptidoglycan

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21
Q

What is an endotoxin

A

A component of the outer membrane of bacteria
- e.g. lipopolysaccharide in gram -ve bacteria.

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22
Q

What is exotoxin

A
  • A target specific cellular component
  • secreted by both gram +ve and -ve
  • e.g. tetanus toxin targets the nervous system ➡️ muscle rigidity
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23
Q

What is an exotoxin made of

A

Protein

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24
Q

What is an endotoxin made of

A

Lipopolysaccharide

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25
Q

How do the action of exo and endotoxins differ

A
  • Exotoxins have specific actions
  • Endotoxins have non-specific actions
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26
Q

T/F
Both endotoxins and exotoxins are heat labile

A

False
Endotoxins are stable under heat

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27
Q

T/F
Both gram +ve and -ve bacteria produce exo and endotoxins

A

False
- Both produce exotoxins
- only gram -ve produce endotoxins only they have LPS

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28
Q

Which one has strong antigenicity - endotoxins or exotoxins

A

Endotoxins
[exotoxins have weak antigenicity]

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29
Q

What is a toxoid

A

A toxin treated with formaldehyde so that it loses its toxicity but maintains its antigenicity

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30
Q

Which can be converted into a toxoid - endotoxin or exotoxin

A

Endotoxin

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31
Q

How is genetic variation achieved in bacteria

A
  • Genetic mutation
    • Base substitution
    • Deletion
    • Insertion
  • Gene transfer
    • Transformation eg via plasmid
    • Transduction eg via phage
    • Conjugation eg via sex pilus
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32
Q

What is the first level of bacterial classification

A
  • Obligate intracellular bacteria Vs
  • Bacteria that may be cultured on artificial media
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33
Q

Examples of obligate intracellular bacteria

A
  • rickettsia
  • chlamydia
  • Coxiella
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34
Q

Describe the stages of gram staining

A

Come In And Stain
1. Fixation of clinical materials to microscope slide using heat/methanol
2. Application of primary stain: Crystal violet ➡️ all cells turning purple
3. Application of mordant = Iodine ➡️ crystal violet-iodine complex formed
4. Decolourisation step: distinguishes gram +ve and gram -ve, use Alcohol [acetone or ethanol]
5. Application of counterstain: Safranin to stain gram -ve pink

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35
Q

Purpose of gram staining

A

To determine whether bacteria is gram positive or negative

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36
Q

What is a catalase test used for

A

Used in gram positive cocci to determine whether chains or clusters are present

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37
Q

Catalase +ve test means what is present

A

Staphylococcus
Clusters

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38
Q

Catalase -ve test means what is present

A

Streptococcus
Chains

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39
Q

T/F
Most gram +ve bacteria that commonly cause disease are anaerobic

A

False - most are aerobic

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40
Q

What is the purpose of the coagulase test

A

To differentiate between staph. Aureus Vs staph epidermidis/ staph. saphrophiticus

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41
Q

Coagulase +ve test indicates the presence of…

A

Staph aureus

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42
Q

Coagulase -ve test indicates the presence of…

A

staph epidermidis or staph. saphrophiticus

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43
Q

What is blood agar haemolytic used for

A
  • to determine the type of gram positive streptococcus
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44
Q

What are the possible outcomes of haemolysis on blood agar

A
  • alpha haemolytic
    • partial lysis ➡️ green streaks on agar
  • beta haemolytic
    • complete lysis ➡️ colourless streaks on agar
  • gamma haemolytic
    • no lysis ➡️ no colour change
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45
Q

How do the blood agar haemolysis test yield results

A
  • alpha haemolysis ➡️ green streaks because these bacteria produce hydrogen peroxide which partly breaks down haemoglobin
  • beta haemolysis ➡️ colourless streaks because these bacteria produce streptolysin [O or S] and that fully breaks down haemoglobin
  • gamma haemolysis ➡️ no change as there is no agent that affects haemoglobin
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46
Q

When is antigenic servo grouping used

A

Only in beta haemolytic strep groups

47
Q

What is antigenic sero grouping

A
  • the test for Carbohydrate cell surface antigens
  • Lancefield groups A-H and K-V
48
Q

Which sero-groups are most important

A

Groups A and B

49
Q

Example of a group A strep

A

Strep. Pyogenes

50
Q

How bacteria classified into antigenic groups

A

Lancefield microbead agglutination test
- Antiserum (antibodies) made that recognise each group are tagged to tiny plastic beads
- they added to a suspension of bacteria
- Antibodies bind bacteria and beads clump together
- Visible to naked eye

51
Q

What is the optochin test used for

A

To differentiate between alpha haemolytic strep bacteria
- strep. Pneumonia OR
- Strep. Viridens

52
Q

Optochin sensitive bacteria indicates presence of …

A

Streptococcus pneumoniae

53
Q

Optochin resistant bacteria indicates presence of …

A

Streptococcus viridens

54
Q

What is MacConkey agar
and what is it used for

A
  • A selective and differential culture medium for bacteria
  • used to selectively isolate gram negative enteric bacteria AND differentiate them based on ability to ferment lactose
55
Q

Colourless/ yellow MacConkey agar =

A

Non-lactose fermenting bacteria present

56
Q

Pink MacConkey agar =

A

Lactose fermenting bacteria present

57
Q

What colour does a non lactose fermenting bacteria show up as on MacConkey agar

A

Colourless / yellow

58
Q

What colour does a lactose fermenting bacteria show up as on MacConkey agar

A

Pink

59
Q

T/F

MacConkey agar can be used for gram -ve bacilli and cocci

A

FALSE
Only used for gram -ve bacilli

60
Q

Give 3 examples of lactose fermenting bacteria

A

E.coli
Enterobacter
Klebsiella

61
Q

What is the oxidase test used for

A

Oxidase test is used to determine if a bacterium produces certain cytochrome c oxidases - enzyme used in electron transport chain.
this means the bacteria is aerobic
- therefore oxidase test tests for aerobic or anaerobic bacterium

62
Q

Outcome of a +ve oxidase test

A

Blue end product produced = aerobic bacterium

63
Q

Outcome of a -ve oxidase test

A
  • no colour change = anaerobic
  • e.g:
    • shigella
    • salmonella
    • proteus
64
Q

2 examples of oxidase -ve bacteria

A
  • shigella
  • salmonella
65
Q

An example of oxidase +ve bacteria

A

Pseudomonas [gram negative bacilli]

66
Q

When would an oxidase test be used?

A

On a gram negative bacilli that has tested negative of MacConkeys agar [colourless] so is non-lactose fermenting

67
Q

What is XLD agar
and how does it work

A
  • A selective growth medium used in the isolation of Salmonella and Shigella
  • the agar contains sugar which can be fermented be salmonella but not shigella ➡️ differentiation
68
Q

What is XLD agar used for

A

To differentiate between shigella and salmonella
- shigella ➡️ red/pink colonies on red agar
- salmonella ➡️ black colonies on red agar

69
Q

What is the Ziehl-Neelson stain

A

A stain used to identify acid fast organisms, mainly mycobacteria

70
Q

What colour are positive and negative ziehl-neelson stains

A
  • positive = pink
  • negative = blue / colourless
71
Q

What does a positive Ziehl Neelson test indicate

A

Presence of acid fast bacteria = mycobacteria

72
Q

When would you use a ziehl-neelson stain

A

To test a sample of rods

73
Q

T/F
Ziehl-neelson stain can be used on rods, cocci and spirochaetes

A

FALSE
- only used on rods

74
Q

what is chocolate agar

A

heated to 80C for breakdown of haem & release of factors that grow organisms w/ fastidious growth requirements [H.influenzae]

75
Q

what is CLED agar

A
  • cysteine lactose electrolyte deficient agar - contains cytosine + lactose
  • a non-inhibitory growth medium that differentiates between organisms in urine & allows classification of lactose fermenting [yellow] & non lactose fermenting [blue] gram-negative bacilli
76
Q

what is blood agar

A

agar with horse/sheeps blood
used for growing lots of bacteria
least selective

77
Q

What is MacConkey Agar

A

grows gram negative bacilli (it has bile salts that inhibit the growth of gram positive). Has lactose & red dye

lactose fermenting = pink colonies
non lactose fermenting = white colonies

78
Q

What is Gonococcus Agar?

A

Contains growth factors to promote the growth of Neisseria species as well as antibiotics & antifungal agents to inhibit the growth of other organisms

79
Q

What is Sabouraud’s Agar?

A

used to culture fungi. Has antibiotics to inhibit bacterial growth.

80
Q

What is XLD Agar?

A
  • a selective growth medium used to isolate Salmonella and Shigella [non lactose fermenting, gram negative].
  • most other gut bacteria turn the agar yellow.
  • Salmonella - Red with black centre (produces H2S)
  • Shigella - Red only
81
Q

What colour will Staphylococcus aureus appear on blood agar and what colour would other staphylococcus species appear?

A

S.aureus - gold
S.other - white

82
Q

How can you tell the difference between various Gram Positive bacteria?

A

+tve Catalase Test = Staphylococcus:
(if positive then do Coagulase Test:)
+tve = S.aureus
-tve = S.epidermidis/S.saprophyticus

-tve Catalase Test = Streptococcus
(if negative then do Haemolysis on blood agar)

alpha haemolysis (partial/green) = requirement for Optochin Test
Optochin Sensitive = S.pneumoniae
Optochin Resistant = S. viridans group

Beta haemolysis (full) = requirement for Lancefield grouping via serology)
A = S.pyogenes
B = S.agalactiae
A,C, G = Tonsilitis, pharyngitis, skin infection
B = Neonatal sepsis + meningitis

Gamma Haeomolgysis (none) = Enterococcus

83
Q

How can you tell the difference between various Gram Negative bacteria?

A

MacConkey Agar for lactose fermentation Test:
+tve lactose fermentation = E.coli/Klebsiella
-tve Lactose fermentation = Requirement to do Oxidase Test

Oxidase Test:
+tve Oxidase = Pseudomonas, Aueruginosa
-tve Oxidase = Requirement to do XLD test:

Colonies on XLD which are Red with black centers = Salmonella
Colonies on XLD which are Red only = Shigella

84
Q

What are the 2 main approaches to diagnosing viral infection?

A

Electron Microscopy / PCR
Serology Testing - ELISA, IF, Complement Fixation Test.

85
Q

What is an advantage and disadvantage to PCR?

A

Very fast but high risk of false positives as it is very sensitive and so can easily be contaminated.

86
Q

What is an advantage and disadvantage to ELECTRON MICROSCOPY testing?

A

Very specific and sensitive but too expensive and too long

87
Q

What is a differential Diagnosis to Glandular fever and how is this ruled out?

A

S.pyogenes throat infection - Both EBV and S.pyogenes present with purulent (pus) infection over the tonsils

Take black charcoal swab to rule out S.pyogenes

88
Q

What is BALF?

A

Bronchoalveolar lavage fluid

Fluid collected from the lungs
Bronchi are washed and this fluid is sent for analysis using PCR

89
Q

What condition can cytomegalovirus cause?

A

CMV colitis
Characteristic finding is OWL EYE INCLUSION BODIES

90
Q

What is the treatment for CMV infection?

A

IV ganciclovir

91
Q

What HIV markers can be found in the blood

A

HIV Igs
HIV RNA
p24 antigen

92
Q

What is chocolate agar

A

blood agar that’s been cooked to release the contents of RBCs

93
Q

what pathogen grows exclusively on chocolate agar

A

haemophilus influenzae
[loves haem]

94
Q

what samples would you collect for suspected community acquired pneumonia

A

sputum and blood culture

95
Q

what does A show

A

beta haemolysis

96
Q

what does B show

A

alpha haemolysis

97
Q

what does C show

A

no haemolysis or gamma haemolysis

98
Q

what is the most common causative pathogen of CAP

A

streptococcus pneumoniae

99
Q

what is invasive pneumococcal disease
who is most susceptible to IPD

A
  • strep. pneumoniae that goes beyond the respiratory tract, e.g. into the blood
  • immunocompromised pts, pts who smoke.
100
Q

what is CURB-65 and what is it used for

A
  • a severity score that indicates risk of death secondary to CAP.
  • used to guide antibiotic treatment.
    C = confusion/delerium
    U = urea >7mmol/L
    R = Respiratory rate ≥30
    B = Blood pressure: diastolic ≤60 OR systolic<90
    Age = >65
101
Q

in what scenario is an infection caused by legionella most likely

A

pts that have been abroad and around AC - e.g. Spain.

102
Q

what samples are collected for suspected legionella infection

A

blood for culture
urine for urinary legionella antigen test [like a lateral flow]

103
Q

what makes an atypical pathogen atypical

A
  • less common
  • not easily cultured
  • can’t be seen on gram film
  • don’t respond to beta lactams abx
104
Q

classical causes of CAP

A
  • strep pneumoniae
  • H. influenzae
  • mortadella catarralis
105
Q

what samples would you take for an acute exacerbation of COPD

A
  • sputum sample - for bacterial culture
  • throat swab for virus PCR
106
Q

what is never the first line treatment for atypical CAP and why

A

amoxicillin
atypical pathogens are not sensitive to beta lactams

107
Q

what is ziehl Nelson staining and what pathogen does it find

A
  • a staining method used for acid and alcohol fast bacteria.
  • most commonly find mycobacteria - TB
108
Q

what is an alternative better way of detecting mycobacteria
+ what are the benefits

A
  • auramine phenol fluorescent stain using a flurescent microscope.
  • more sensitive and faster than Ziehl Neelson
109
Q

what medium is used to grow mycobacteria

A

Lowenstein Jensen Slope.
- Contains nutrients that promotes mycobacterial growth.
- contains antimicrobial agents to prevent growth of other organisms. e.g. penicillins

110
Q

histological finding from a lymph node biopsy that indicates TB

A

caseating granulomata

111
Q

what is a common causative pathogen of pneumonia in HIV pts or immunocompromised pts

A

pneumocystis jiroveci - a fungus

112
Q

how is a microbial sample of the lower lungs obtained for sample in lower respiratory tract infections

A
  • brocho alveolar lavage = looking down into the lungs and a saline solution is put through the bronchoscope to wash the airways and collected as a fluid sample
  • induced sputum sample = breathing in different concentrations of saline through a nebuliser and then carrying out cough-like movements to produce a sample of sputum.
113
Q

what type of pathogens can be treated with co-trimoxazole

A
  • bacteria
  • fungi
  • Protozoa
    combo of trimethoprim and sulfamethoxazole
    [tri = 3 different pathogen types]
114
Q

what CD4 count is indicative of AIDs

A

<200

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