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MBIO 3010 > Section 10 > Flashcards

Section 10 Flashcards

1
Q

What are the 2 goals of a clinical microbiology laboratory?

A
  • Identification of the microorganism in the patient specimen that is involved in the disease process
  • Provide antimicrobial susceptibility of the isolated microorganism
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2
Q

How can microorganisms be identified in a patient specimen?

A

1) Identify microorganisms by isolation & culture
2) Identify a specific microbial gene or product
3) Detect specific antibodies to a pathogen

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3
Q

____ infections need immediate treatment

A

Bloodstream

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4
Q

What should be done when testing CSF?

A

Design a primer that is specific to the gene you want to test

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5
Q

What can be done once an organism has been isolated in culture?

A

Its susceptibility to antimicrobial agents can be determined

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6
Q

How can you tell the difference between MSSA and MRSA?

A

Outcome of an infection

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7
Q

What type of identification process is common among tuberculosis diagnosis?

A

Detection of antibodies

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8
Q

When would detection of antibodies be used?

A
  • Pathogens that can’t be cultivated

- High risk group pathogens

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9
Q

What is important to do before testing for antibodies against a pathogen?

A

Ask the patient if they have had a vaccine against that infection, because if they have been vaccinated they will have antibodies against it but won’t necessarily be infected

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10
Q

What is extremely important to know when processing specimens?

A

Where the sample came from because you need to know if it came from a sterile site or a site with commensal flora

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11
Q

What are disadvantages to culture-based methods?

A
  • At least 18 hours to see colonies
  • Slow-growing organisms
  • Not every organism can be cultured
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12
Q

What is the problem with blood cultures?

A

Always incubated for 5 days because numbers can be very low, but blood infections need immediate treatment

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13
Q

_____ is the gold standard for ruling in/out infectious agents

A

Culturing

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14
Q

Many non-culture methods are _____ based

A

Test tube

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15
Q

What are advantages to non-culture methods?

A
  • Fast
  • Less lab intensive
  • Suitable for organisms that cannot be cultured in the lab
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16
Q

What are 2 types of non-culture methods?

A
  • Immunodiagnostics

- Molecular diagnostics

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17
Q

What is generally the first step of diagnostics?

A

Microscopy

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18
Q

What does light microscopy do?

A

Magnifies objects and therefore improves the resolving power of the naked eye to 200 nm

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19
Q

What is bright field light microscopy used for?

A

To examine specimens & cultures as wet or stained preparations

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20
Q

What are the steps of a gram stain?

A
  • Crystal violet
  • Iodine
  • Ethanol wash
  • Safranin
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21
Q

Why is iodine used in a gram stain?

A

To make sure the stain sticks (iodine forms a complex with a crystal violet and makes it trapped in cell wall)

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22
Q

Why is an ethanol wash used in a gram stain?

A

To poke holes in the membrane and dissolve lipid so crystal violet can be lost from cells with thin peptidoglycan

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23
Q

What information does a gram stain give?

A
  • Cell wall or not
  • Structure of membrane
  • Morphology (shape)
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24
Q

Are gram stains the only stains that can show morphology?

A

No, any type of stain can show morphology

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25
What is the gram sign and morphology of staph aureus?
- Gram positive | - Cocci in clusters
26
What is the gram sign and morphology of lactobacillus?
- Gram positive | - Rods
27
A healthy vagina should have high amounts of _____ organisms
Gram positive
28
What do acid fast stains detect and why?
Mycobacteria (organisms that carry mycolic acid in their cell walls) because they have a waxy cell wall that doesn't take up a gram stain
29
What happens once an organism with mycolic acid is stained?
It will be stained forever
30
Acid fast stains are generally used for ____
Tuberculosis
31
How are fluorescent stains viewed?
In a microscope with a UV light source instead of white light
32
What is the easiest and fastest way to test for tuberculosis?
Fluorescent staining
33
Define resolution
The minimum distance between 2 objects that the eye can determine them as 2 distinct objects
34
What is the resolution of electron microscopes?
0.1 - 1.0 nm
35
What is the resolution of the naked eye?
100,000 nm
36
What is found in an electron microscope?
- A beam of electrons instead of a beam of light | - Magnets instead of lenses
37
What is the difference between SEM and TEM?
- SEM shows surface structures | - TEM shows internal structures
38
What is helpful in identification of viruses?
Electron microscopy
39
Are electron microscopes used in clinical labs?
Not usually
40
_____ is much more rapid than culturing
Immunodetection
41
What is immunodetection generally used for and why?
CNS infections because they are very serious and diagnostics need to be carried out fast
42
When does clumping occur?
When a specific Ag that is present on a bacterial cell surface is added to its corresponding Ab that is coated onto a latex bead
43
What are 3 common causes of bacterial meningitis?
- Streptococcus pneumoniae - Haemophilus influenza - Neisseria meningiditis
44
When can a false positive occur in immunodetection?
When Ab and Ag aren't equal in the specimen
45
Immunodetection is a _______ method
Qualitative
46
When is immunodetection useful?
When the patient has received antibiotics and organisms may appear morphologically unidentifiable in CSF and fail to grow in culture
47
What is ELISA?
Enzyme-linked immunosorbent assay
48
How do ELISA work?
By detecting Abs for a pathogen
49
How are secondary Abs tagged?
By the enzyme ELISA
50
Where do secondary Abs bind to?
Fc region
51
How can ELISA be quantified?
Spectrophotometry
52
Why is gene detecting a method of diagnostics?
Because if the specific gene is present, then you can assume that the organism is present
53
Describe probe-based methods
- Labeled, single-stranded nucleic acid fragments are made to hybridize with the target DNA - H bonds form between bases
54
How long should probes be?
- Long enough to show specificity | - Short enough so that the probe doesn't have self-binding
55
Are probe-based or amplification-based methods more advantageous and why?
Amplification-based methods because they are independent of the number of infectious agents in the body
56
What do selective media do?
Select against specific pathogens
57
What does mannitol salt agar do?
Allows growth of gram positive organisms and inhibits growth of gram negative organisms
58
What type of media should be used for a sample taken from a place with a lot of normal microflora?
Selective
59
What does differential media do?
Has a metabolic indicator that allows differentiation between 2 organisms without inhibiting anything
60
What is the most common differential medium?
Blood agar plates
61
What does alpha hemolysis mean?
Partial hemolysis of RBC's
62
What does beta hemolysis mean?
Complete hemolysis of RBC's
63
What does gamma hemolysis mean?
No hemolysis of RBC's
64
What is the cytopathic effect used for?
Obligate intracellular organisms
65
What is the catalase test used to differentiate between?
Streptococcus and staphylococcus species
66
What are some characteristics of Neisseria?
- Gram negative - Cocci in pairs - Oxidase positive
67
For biochemical tests, what does a change in colour mean?
Metabolism (acid production)
68
What is the "metabolic fingerprint" of an organism?
The results of different tests for that organism

MBIO 3010 (17 decks)

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