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Diagnostics > 3. Bacteriology lab > Flashcards

3. Bacteriology lab Flashcards

1
Q

What is endocarditis (SBE)?

A
  • (subacute bacterial) Endocarditis
  • Infection of the inner lining of the heart
  • Affects the heart valves too
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2
Q

What are common bacterial STIs?

A
  • Gonorrhoea
  • Syphilis
  • Chlamydia
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3
Q

What is brucellosis?

A
  • Disease caused by Brucella
  • Passed from animals to humans
  • Also caused by ingestion of unpasteurised milk or undercooked meat
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4
Q

Where is Meliodosis (gram-negative) likely to be picked up from?

A
  • Far-east

* Soil and water

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5
Q

What are common diagnostic techniques in the bacteriology lab?

A
  • Culture of sterile sites (blood/CSF) and non-sterile sites (bowel/skin)
  • Serology - immune response to infection
  • Molecular techniques e.g. PCR
  • Antimicrobial Susceptibility Testing
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6
Q

How long do you culture blood for?

A

About 5 days

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7
Q

How do you test for bacteria to perform a blood culture?

A
  • Take blood from patient and put in 2 different bottles (aerobic and anaerobic)
  • Blood incubated at a temperature similar to body temperature - bacteria multiplies
  • Bacteria reproduces and produces CO2 - pH and colour change on disc at the bottom of the bottles
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8
Q

Once tested positive in a bottle, how can blood be cultured?

A

• Put onto different agar plates
- blood agar
- chocolate agar (haemolysed blood)
- MacConkey agar
- neomycin agar
• Different bacteria use different salts and nutrients
• Most bacteria can grow on blood/chocolate agar
• Gram negative grow on MacConkey (produces a colour change)
• Plates incubated for 24 hours

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9
Q

How can you distinguish between gram positive and negative bacteria?

A

• Gram stain
• Gram positive - thick peptidoglycan wall
- purple/blue
• Gram negative - thin peptidoglycan wall, sandwiched by 2 membranes
- pink/red

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10
Q

What is the coagulase test - when is it used?

A

• There are different types of staphylococcus
- on the skin - coagulase negative (normally not a problem)
• Some strains may contain the enzyme coagulase
• If positive - it’s staphylococcus aureus
• Coagulase changes fibrinogen => fibrin in our blood

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11
Q

What can commensals like staphylococcus infect?

A 
• Low pathogenic potential
• However, can:
- infect prosthetic material
- cause (central) line infections
- pacemaker infections
- endocarditis
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12
Q

How can you tell if streptococci is alpha or beta-haemolytic, and give an examples of each?

A

• Alpha - produces a green tinge to the blood agar
- e.g. streptococcal pneumonia
• Beta - use up all the blood (haemolytic)
- e.g. group A streptococcus

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13
Q

Which type of bacteria should we worry about causing a septic shock?

A
  • Gram negative (rod)

* Outer membrane can produce toxins and cause shock

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14
Q

Which bacteria, parasites and viruses can cause diarrhoea?

A 
Bacteria
• Salmonella (S. typhi)
• Shigella
• Campylobacter
• E. coli
• C. difficile
• Cholera

Parasites
• Amoeba
• Giardia
• Cryptosporidium

Viruses
• Norovirus

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15
Q

Which bacteria are looked for routinely in stool samples?

A
  • Salmonella
  • Shigella
  • Campylobacter

Cultured on agar plates

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16
Q

Which bacteria from stool samples can’t be cultured, and what is done instead?

A
  • Clostridium difficile

* Toxin detection or PCR for toxin gene instead

17
Q

What does sensitivity testing refer to?

A

Looking for the point at which bacteria is sensitive or resistant to a specific concentration of drug

18
Q

What is the minimum inhibitory concentration (MIC)?

A

Lowest amount of antibiotic required to inhibit the growth of bacteria in vitro

19
Q

How can you test the MIC and general sensitivity?

A
  • Perform doubling dilution of antibiotics
  • Look at point at which bacteria starts growing

e.g.
• Incorporate antibiotic into a strip, with different concentrations at each point
• Place on agar
• Where the bacteria stop growing to the furthest point is the MIC

  • Disc diffusion
  • The bigger the circle around the antibiotic soaked disc, the more sensitive the bacteria is
20
Q

What are beta-lactamases?

A
  • Enzymes that bacteria have
  • Allows bacteria to survive against their environmental competitors
  • There are different types of beta-lactamases
  • Antibiotics have helped evolve bacteria
21
Q

Does IgG or IgM respond earlier in an infection?

A

IgM

22
Q

Does IgG or IgM rise after second exposure to an antigen?

A
  • Both rise

* IgG rises more

23
Q

Why may you get a negative serology result for IgG when an infection is present?

A
  • Samples sent too early

* Important to repeat test 2-4 weeks later in these scenarios

Diagnostics (5 decks)

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