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Infectious Disease > Diagnostics > Flashcards

Diagnostics Flashcards

1
Q

What are the types of methods used for identification of microorganisms associated with infectious disease

A
  1. Direct

2. Indirect

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2
Q

Examples of direct methods of microorganism identification

A
  1. Blood
  2. Faeces
  3. Tissue biopsy
  4. Mucosal swab
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3
Q

Examples of indirect methods of microorganism identification

A
  1. blood sample and search for an antibody against a suspected pathogen
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4
Q

what happens after collected sample using direct method

A
  1. speciment collection
  2. Microscopic examination
  3. Microbial detection using
    a) culture based techniques
    b) non culture techniques
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5
Q

When collecting specimen using direct technique how should you collect?

A
  1. Aseptically
  2. representative site
  3. sufficient quantity
  4. Specimens collected prior to antimicrobial therapy to maximise pathogen recovery
  5. If cultures not immediately initiated after collection, specimens must be refrigerated
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6
Q

How do you obtain a representative sample?

A
  1. specimen must be from site containing pathogen

2. adequate volume

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7
Q

Definition of aseptic technique

A

refers to a procedure that is performed under sterile conditions, or to prevent contamination.

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8
Q

Samples are submitted to clinicians. What else must be submitted?

A
  1. complete submission form presumptive diagnosis
  2. must specify: what is the sample type, where swab collected from
  3. Case history
  4. Required test
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9
Q

How is a sample stored?

A
  1. Only do so if necessary
  2. 4oC better than anything cooler or warmer
  3. long-term storage at -80oC or below
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10
Q

How is sample transported?

A
  1. stop bugs from dying
    get the sample to the lab fast!
  2. use “transport medium
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11
Q

Pros of direct method: microscopic observation

A
  1. cost effective lab test
  2. Immediate info on presence/ absence and number of organisms
  3. Provides info on host cellular response
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12
Q

3 ways to prepare a slide for microscope

A
  1. smear using swab
  2. smear using aspirate (spread sample)
  3. Tissue impression smear (biopsy)
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13
Q

What is the msot common sued stain of bacteria?

What categories are the bacteria then divided into?

A
  1. Gram stain
  2. Gram positive = purple stain
  3. Gram negative = pink stain
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14
Q
  1. Before staining what must happen to the smears made from the specimens?
  2. What is the slide then covered by? and how long?
A
  1. Smears must be fixed, usually by passing them trough a Bunsen burner flame 2-3 times.
  2. The slide is then covered with cristal violet for 30 sec, iodine, 60 sec, then decolorized by covering the slide with alcohol for few sec.
  3. Iodine is also used in Gram’s staining, it enhances dye to enter through the pore present in the cell wall/membrane.
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15
Q

What are phenotypic trains of bacteria that help with identification?

A
  1. Staining properties: gram, acid fast, polychrome methylene blue
  2. Oxygen requirements: anaerobic or aerobic?
  3. Culture characteristics: colonial morphology, size, pigmentation
  4. Microscopic morphology: shape, size, cellular arrangement, presence of spores
  5. Biochemical reactions: fermentation reactions, catalase, oxidase, urease
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16
Q

What methods to microbiologists use to identify an unknown pathogen?

A

Methods that fall into 3 categories

  1. Phenotypic based: describing morphology (micro and macroscopic)
  2. Immunological: serological analysis = identification of bac, fungi, virus
  3. Molecular techniques: genetic techniques suitable for slow growing, non culturable, viruses
17
Q

What are different types of media used for bacteria cultivation?

A
  • Enrichment media are general purpose media supplemented by blood or other special nutrients to encourage the growth of fastidious organisms
  • Selective media favour the growth of particular microorganisms and inhibits the growth of others.
  • Differential media distinguish between different groups of bacteria on the basis of their biological characteristics
18
Q

When interpreting the test what are 2 sources of error?

A
  1. test itself: false positive and false negative

2. interpreter of test

19
Q

A perfect test is:

A
  • never positive in a patient who hasn`t got the disease

- never negative in a patient who is in fact diseased

Infectious Disease (9 decks)

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