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Introduction to Medical Microbiology > Lecture 8- Systematics > Flashcards

Lecture 8- Systematics Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Define Systematics

A

the scientific process of characterising micro-organisms in an orderly manner with the aim of providing an identification

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2
Q

What does systematics come under the broad area of?

A

Taxonomy

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3
Q

Define Taxonomy?

A

he orderly classification of organisms into appropriate categories on the basis of relationships among them, with the application of suitable and correct names

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4
Q

Taxonomy comprises three interrelated disciplines, what are they?

A
  • Classification
  • Nomenclature
  • Identification
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5
Q

How are organisms classified in taxonomy?

A
  1. Morphologic traits
  2. Physiological traits
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6
Q

Define Nomenclature?

A

Labeling/naming of the groups and the members

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7
Q

What are the main feature of nomenclature?

A

Names have a Latin or Greek derivation

First letter of genus is always Capitalised (S.aureus or Staphylococcus)

Species designation is always lowercase

Both components are either italicised OR underlined

Genus may be abbreviated to first letter i.e. S.aureus

Species name is never abbreviated

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8
Q

Define Identification

A

the process of characterising the features of an unknown organism and comparing these with the known features of previously characterised organisms so that it can be classified within the most suitable taxa (group) and assigned an appropriate genus and species name.

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9
Q

What are the main steps involved in classification of bacteria?

A
  • Colony morphology (on various media - fastidious nature)
  • Gram reaction (size, shape, colour, arrangement)
  • Atmospheric requirements (AnO2, ̄O2, CO2)
  • Motility
  • Biochemical tests
  • Serological tests
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10
Q

What is Cowan and Steel s Manual for the Identification of Medical Bacteria?

A

A compact book containing an extensive list of sequential tables describing characteristics of both Gram positive AND Gram negative bacteria

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11
Q

What does +, - and D mean in idenditfying medical bacteria?

A

’ -‘ means 0-15% of strains are positive

’+’ means 85-100% of strain are positive

‘D’ means 16-84% of strains are positive (Differential).

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12
Q

What are the general primary identification test performed on medical bacteria

A
  • Shape
  • Acid Fastness
  • Spores (spore stain)
  • Motility
  • Growth in air (O2 - air only contains 21% oxygen)
  • Growth anaerobically (AnO2)
  • Catalase
  • Oxidase
  • Glucose (acid)
  • O-F test
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13
Q

What identification test are not performed on gram negative bacteria?

A

NO Acid Fast stain or spore stain

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14
Q

What bacteria can not have a gram stain done on it

A
  • Chlamydia (intracellular existence)
  • Mycoplasma, Ureaplasma (lack a cell wall)
  • Spirochetes (too small to be resolved by light microscope?)
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15
Q

Describe the method of gram staining

A

Crystal violet (30 sec),

iodine (30 sec),

alcohol (15 sec) or acetone (1-2 sec),

carbol fuchsin (30 sec)

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16
Q

What is the reason for gram stains ability to be differential?

A

Differential staining based on cell wall composition

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17
Q

General charecteristic of a gram positive stain?

A
  • thick layer of peptidoglycan with teichoic acid cross linkages
  • resist decolourisation (crystal violet-iodine complex intact)
  • blue/purple colour
  • coccus/bacillus
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18
Q

General charecteristics of a gram negative stain?

A
  • thin layer of peptidoglycan
  • decolourisation due to disruption of lipid rich outer membrane

and thin layer of peptidoglycan

  • colourless until counterstained
  • pink colour
  • coccus/bacillus/curved/helical
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19
Q

What is the name for an acid fast test?

A

Ziehl-Neelsen Stain

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20
Q

What organisms have a positve test result for a acid fast test?

A

Mycobacterium and Nocardia are positive

  • M. tuberculosis
  • M. leprae
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21
Q

What is general method and what do the colours indicate on an acid fast test

A
  • Concentrated carbol fuchsin and heat
  • Decolourise with acid alcohol
  • Counterstain with methylene blue
  • Acid fast organisms - red/pink
  • Other organisms and background material - blue
22
Q

What is a spore stain?

A

It is a test used for the detection of bacterial spores (only in gram positive)

23
Q

What are the bacteria that will test positive for a spore stain

A

Bacillus and Clostridium are positive

24
Q

Decribe the general method of spore staining?

A
  • Malachite green
  • Counterstain with safranin
  • Spores - green
  • Bacterial cell - red
25
Q

What is the reason for motility?

A

Motility is due to flagella

26
Q

When testing motility in wet preperations what must you be catous of?

A

careful interpretation due to Brownian motion

27
Q

What is the main test for motility in a lab?

A

Hanging drop - coverslip suspended above the slide

28
Q

How do we prove motility for proteus?

A
  • Peritrichous flagella which help it to grow and move across the plate
  • Very strong foul odour
29
Q

Growth anaerobically?

A

absence of molecular oxygen

30
Q

Obligate aerobe?

A

grows in air, requires molecular oxygen for growth, will not grow anaerobically

31
Q

Microaerophilic?

A

requires oxygen for growth but at a lower concentration than is present in the atmosphere (6-16% O2, 2-10% CO2) – generated using a gas pack

32
Q

Obligate anaerobe

A

will only grow in the complete absence of oxygen

33
Q

Facultative anaerobe

A

will grow in the presence or absence of oxygen

34
Q

Capnophilic (carboxyphilic)?

A

grow best with increased carbon dioxide

35
Q

What is catalase?

A

Catalase is an enzyme which catalyses the breakdown of hydrogen peroxide to produce oxygen and water

36
Q

How is a catalase test perfomed?

A

Mix colony material with hydrogen peroxide and observe for the production of effervescence

37
Q

What could contaminate a catalase test to give a weak positive reaction?

A

Weak positive reaction If inoculum is contaminated with RBC (BA)

38
Q

What can be used as a control for a catalase test

A

Use any Staphylococcus sp. as a positive control

39
Q

What results would you expect from a catalase test for the following bacteria staphylococci, streptococci and enterococci (GPC)

A

staphylococci (GPC) = positive

streptococci and enterococci (GPC) = negative

40
Q

What does an oxidase test detect

A

Detects the presence of the enzyme cytochrome oxidase in the bacteria

41
Q

What is the enzyme cytochrome involved in?

A

The enzyme is involved in electron transport and metabolic pathways of some bacteria

42
Q

Describe the method for an oxidase test?

A

Use filter paper that has been presoaked with TMPD and allowed to dry oxidase

reagent (e-) + oxidase + O2 ® indophenol blue (purple < 10 secs)

43
Q

What type of instrument can produce a false negative in an oxidatative test?

A

Any loops or wires containing iron (Use platinum or tooth pick)

44
Q

What are clinically significant genera that are oxidase positive

A

Pseudomonas sp., Vibrio sp., Campylobacter sp., Aeromonas sp., Pasteurella sp., Neisseria sp., Moraxella sp.

45
Q

What does a glucose (acid production) test detect?

A

Detects the presence of acid from the utilisation of glucose through fermentation or oxidation

46
Q

How are the results of a glucose (acid production) test determined

A

Acid production detected by colour change of the pH indicator

  • bromthymol blue (green) to yellow (acid production)
47
Q

What does a Oxidation-Fermentation Test detect

A

Detects whether an organism metabolises glucose by oxidation or fermentation (requires oxygen)

48
Q

What is fermentation?

A

Fermentation is the anaerobic metabolism of glucose

49
Q

What are the indicators for a Oxidation-Fermentation Test?

A

Utilisation of glucose produces acid

  • bromthymol blue pH indicator (green) to yellow (acid)
50
Q

What do the two tubes contain in an Oxidation-Fermentation Test

A

Test utilises two tubes

  • 1% glucose with a loose lid (oxygen present)
  • 1% glucose with a layer of paraffin (oxygen absent)
51
Q
A

Introduction to Medical Microbiology (7 decks)

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