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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
Q

What is the gram sign and morphology of staph aureus?

A
  • Gram positive

- Cocci in clusters

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26
Q

What is the gram sign and morphology of lactobacillus?

A
  • Gram positive

- Rods

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27
Q

A healthy vagina should have high amounts of _____ organisms

A

Gram positive

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28
Q

What do acid fast stains detect and why?

A

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
Q

What happens once an organism with mycolic acid is stained?

A

It will be stained forever

30
Q

Acid fast stains are generally used for ____

A

Tuberculosis

31
Q

How are fluorescent stains viewed?

A

In a microscope with a UV light source instead of white light

32
Q

What is the easiest and fastest way to test for tuberculosis?

A

Fluorescent staining

33
Q

Define resolution

A

The minimum distance between 2 objects that the eye can determine them as 2 distinct objects

34
Q

What is the resolution of electron microscopes?

A

0.1 - 1.0 nm

35
Q

What is the resolution of the naked eye?

A

100,000 nm

36
Q

What is found in an electron microscope?

A
  • A beam of electrons instead of a beam of light

- Magnets instead of lenses

37
Q

What is the difference between SEM and TEM?

A
  • SEM shows surface structures

- TEM shows internal structures

38
Q

What is helpful in identification of viruses?

A

Electron microscopy

39
Q

Are electron microscopes used in clinical labs?

A

Not usually

40
Q

_____ is much more rapid than culturing

A

Immunodetection

41
Q

What is immunodetection generally used for and why?

A

CNS infections because they are very serious and diagnostics need to be carried out fast

42
Q

When does clumping occur?

A

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
Q

What are 3 common causes of bacterial meningitis?

A
  • Streptococcus pneumoniae
  • Haemophilus influenza
  • Neisseria meningiditis
44
Q

When can a false positive occur in immunodetection?

A

When Ab and Ag aren’t equal in the specimen

45
Q

Immunodetection is a _______ method

A

Qualitative

46
Q

When is immunodetection useful?

A

When the patient has received antibiotics and organisms may appear morphologically unidentifiable in CSF and fail to grow in culture

47
Q

What is ELISA?

A

Enzyme-linked immunosorbent assay

48
Q

How do ELISA work?

A

By detecting Abs for a pathogen

49
Q

How are secondary Abs tagged?

A

By the enzyme ELISA

50
Q

Where do secondary Abs bind to?

A

Fc region

51
Q

How can ELISA be quantified?

A

Spectrophotometry

52
Q

Why is gene detecting a method of diagnostics?

A

Because if the specific gene is present, then you can assume that the organism is present

53
Q

Describe probe-based methods

A
  • Labeled, single-stranded nucleic acid fragments are made to hybridize with the target DNA
  • H bonds form between bases
54
Q

How long should probes be?

A
  • Long enough to show specificity

- Short enough so that the probe doesn’t have self-binding

55
Q

Are probe-based or amplification-based methods more advantageous and why?

A

Amplification-based methods because they are independent of the number of infectious agents in the body

56
Q

What do selective media do?

A

Select against specific pathogens

57
Q

What does mannitol salt agar do?

A

Allows growth of gram positive organisms and inhibits growth of gram negative organisms

58
Q

What type of media should be used for a sample taken from a place with a lot of normal microflora?

A

Selective

59
Q

What does differential media do?

A

Has a metabolic indicator that allows differentiation between 2 organisms without inhibiting anything

60
Q

What is the most common differential medium?

A

Blood agar plates

61
Q

What does alpha hemolysis mean?

A

Partial hemolysis of RBC’s

62
Q

What does beta hemolysis mean?

A

Complete hemolysis of RBC’s

63
Q

What does gamma hemolysis mean?

A

No hemolysis of RBC’s

64
Q

What is the cytopathic effect used for?

A

Obligate intracellular organisms

65
Q

What is the catalase test used to differentiate between?

A

Streptococcus and staphylococcus species

66
Q

What are some characteristics of Neisseria?

A
  • Gram negative
  • Cocci in pairs
  • Oxidase positive
67
Q

For biochemical tests, what does a change in colour mean?

A

Metabolism (acid production)

68
Q

What is the “metabolic fingerprint” of an organism?

A

The results of different tests for that organism

MBIO 3010 (17 decks)

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