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Medical Microbiology I > Practical Sessions > Flashcards

Practical Sessions Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Susceptibility of a microrganism to anitbiotics cannot…

A

Be predicted sometimes. This is can be due to the resistance that they form towards antibiotic

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2
Q

Why do microrganisms form resistance towards antibiotics?

A

a) Exposure of the microbe to many agents especially micro-flora that reside in the body

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3
Q

Drugs selcted to treat patients must be….

A

a) must be effective in treating
b) have less impact of the patient
c) should not disruot the microflora of the body

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4
Q

A laboratory test done to determine the effectiveness of the antibiotic administeration against specific pathogens

A

Antibiotic Sensitivity Test

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5
Q

Why is antibiotic sensitivity testing done?

A

a) Allow control of antibiotic use in clinics
b) Helps with the knowledge of which drug to prescribe
c) Allows one to view changes in antibiotic therapy of certain microbes (resistance)

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6
Q

In which cases should antibiotic senstivity test be performed?

A

a) When the patient is immunodeficient therefore can contract to many pathogens
b) When the condition being treated can cause death
c) When the pattern of antimicrobial sensitivity is unknown
d) To check resistance patterns of microbes to specific drugs

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7
Q

In which cases is antibiotic sensitivity test not perfomed?

A

a) When the pathogen has a known sensitivity pattern

b) When there are mixed cultures therefore contamination is present

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8
Q

What is a disadvantage of the E-test?

A

Is that individual test strip are needed for each antibiotic thus can be very costly

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9
Q

What is the deal with the Broth Dilution Method?

A

It is beneficial in the determinning of the minimum inhibitory concentration of the antibiotic

It’s disadvantages is that it will be time consuming in the sense that one has to expose the microbe to varing amounts of antibiotic one at a time

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10
Q

What is the limit of the Disk Diffusion?

A

It cannot be used to test slow growing bacteria

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11
Q

Why is there a limitation in the Antibiotic Sensitivity Test?

A

It is because it doesn’t reflect the same sensitivity because the patient’s exposure to the pathogen maybe extensive in terms of development of new ways in which the pathogen evades the immune system

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12
Q

In the identification of bacteria what does one start with?

A

Gram staining and then observing the shape of the bacteria either cooci or rod

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13
Q

pH indicators serve what purpose?

A

They are used in fermentation reaction where there is change of colour depending on the fermentation - acidic or alkaline

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14
Q

Glucose, lactose, …. and …. are used in carbohydrate fermentation

A

Mannitol and maltose

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15
Q

Which agar utilize carbohydrate fermentation?

A
  • MacConkey Agar
  • Mannitol Salt Agar
  • Triple Sugar Iron Agar
  • Mueller Hinton Agar
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16
Q

Why is the Mannitol Salt Agar a selective and differential test?

A

Because it consists of NaCl which is used to only allow for the growth of Staphylococcus spp

It is differential because it consists of mannitol which is a sugar that Staphylococcus aureus can ferment. So it allows for differentiation of S. aureus and other S spp

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17
Q

The MacConkey Agar consists of which carbohydrate?

A

Lactose

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18
Q

How can one differentiate lactose fermentators to non lactose fermenters?

A

Lactose fermenters : They produce lactic acid therefore causing the decrease in pH and cause a change in colour: They form Red colonies

Non lactose fermenters: They do not produce lactose therefore no change in colour : they from cream colonies

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19
Q

What is the function of the catalase enzyme?

A

It catalyzes the breakdown of hydrogen peroxide to water and O2.

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20
Q

For the catalase test how would one know that the test is + or - ?

A

+ Catalase = formation of bubbles

- Catalase = no bubbles are formed

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21
Q

In the catalase test what can produce a false positive?

A

Enterococci, consists of peroxidase enzyme which can catalyse H2O2 to H2O and Oz but at a much slower rate

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22
Q

What is the purpose of the coagulase test?

A

It is used to differentiate Staphylcoccus aureus from other Staphylococci spp

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23
Q

S aureus produces two forms of coagulase, what are they?

A

Bound and Free

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24
Q

What is bound coagulase?

A

An enzyme located on the cell wall of the S aureus and it reacts with fibrinogen directly. After reaction is causes the fibrinogen to attach itself onto the wall of the S aurerus thus causing it to clump when mixed with plasma

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25
Q

What is free coagulase?

A

It is an outside of the cell protein that causes clumping when S aureus is placed with plasma

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26
Q

What coagulase enzyme causes activation of plasma coagulasee reacting factor (CRF), which is then altered to form coagulase CRF complex?

A

Free coagulase

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27
Q

How would one know the coagulase test is +?

A

There will be clumping in less than 10 seconds

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28
Q

When the coagulase test comes back -, how would one confirm 100% that it is -?

A

Use the tube test.

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29
Q

Explain the concept of the tube test?

A

It is used to for confirming if the coagulase test is really negative.

If the test is negative after 4 hrs then place it again for another 24 hrs

if the - then no clots form

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30
Q

Describe the mechanism of the DNAase test?

A

It is used to differentiate S aureus from other S species

It works in such a way that pathogen consists of enzymes known as DNAses that break down DNA in the presence of HCl in order to use the DNA for energy and growth

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31
Q

If the DNAse test is + then….

A

There are clear zones formed

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32
Q

Functions to

a) Differentiate S. agalacataie from other Streptococci species
b) Used to identify L. monocytogenes

A

The CAMP test

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33
Q

Wht does CAMP factor do?

A

It is used to enlarge the area of hemolysis formed

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34
Q

Novobiocin Sensitivity Test

A

It is used to differentiate coagulase - Staphylococcus

It is used to identify S. epidermis from S. saprophyticus

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35
Q

Has a clear zone more than 12 mm is…

A

Novobiocin sensitive

Staphylococcus epidermis

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36
Q

Has a zone of inhibition less than 12 mm or none is….

A

Novobiocin resistant

Staphylococcus saprophyticus

37
Q

Used to identify group A beta Streptococcus

A

Bacitracin Sensitivity

38
Q

Any zone of inhibition

A

+ meaning sensitivity to the Bacitracin

39
Q

What is esculin?

A

It is a substance whose role is to act as an antioxidant

40
Q

Why is the bile esculin agar selective and differential?

A

Because it consists of Oxygall that only allows for the gram - bacteria

It also consists of sodium aziade which is used to inhibit the growth of gram - bacteria

41
Q

The Bile Esculin Agar is used for?

A

It serves to identify Group D streptococci by checking the ability of the pathogen to hydrolyse esculin in the presence of bile

42
Q

By hydrolysing Esculin what is gained or what is the function of the hydrolyses?

A

Changes in the colour of the agar slant to dark brown or black indicating test is +

43
Q

Causes the lysis or breakdown of the cell wall of ??

A

Optochin, Streptococcus pneumonaie

44
Q

+ Optochin sensitvity

A

The zone of inhibition is 14 mm or >

45
Q

What are the types of hemolysis?

A

Partial - alpha hemolysis
Complete - beta hemolysis
None- gamma hemolysis

46
Q

a) Green partial colonies
b) Clear colonies
c) Blue/ no change in colour

A

a) Alpha hemolysis
b) Beta hemolysis
c) Gamma hemolysis

47
Q

What is the function of the oxidase enzyme?

A

It acts to break down amines to form amino acid

48
Q

It is used to differentiate enterobacteria from non enterobacteria

A

Oxidase test

49
Q

Cytochrome C enzyme found in mitochondria or in bacteria that…

A

It is used to for the transfering to electrons from O2 in order to form H2O. Used in the synthesis of ATP

50
Q

+ oxidase test

- oxidase test

A

+ = change of colour to purple

  • = no change in colour
51
Q

Pseudopodes Need Vigo: coin saying for oxidase + pathogens

A

Pseudomona
Nesseria
Vibrio

52
Q

Explain the concept of gelatin liquefication?

A

Tests for the presence of gelatinase enzyme which breaks down large polypeptides in the gelatin to free amino acids thus liquifying it

53
Q

What micro-organisms has the ability to liquify gelatin?

A
  • Vibrio cholerae
  • Serratia species
  • Proteus vulgaris
54
Q

What carbohydrates does the Triple Sugar Iron Test use?

A

Gluocse and lactose

55
Q

What is the purpose of the TSIA test?

A

It is used to differentiate lactose fermenters fro non lactose fermenters

It also serves to differentiate non lactose fermenter in their ability to move and produce Hydrogen sulfide

56
Q

What is unique about the TSIA test?

A

The agar is slanted

57
Q

If the pathogen does not utilise carbohydrates then?

A

Alkaline slant(medium is red) with no change at the bottom

58
Q

If the pathogen only uses glucose?

A

Alkaline slant(medium is red) with acidic buttom

59
Q

If the pathogen uses all carbohydrates?

A

Acid slant(medium is yellow) with acidic bottom

60
Q

If the bottom of the tube is black? Give an example of a pathogen with an alkaline slant but acidic butt with H2S production?

A

Ability to produce H2S

Salmonella

61
Q

What makes the H. influenzae pathogen unique?

A

It requires X factor (( hemin) and V factor ( NAD) for growth

62
Q

+ Factor X and V

A

Growth in presence of X factor and V factor or growth in X factor but not V

63
Q

What are the pH indicators required for TSIA test?

A

Phenol red and ferrous sulphate

64
Q

If the bacteria has the ability to ferment glucose, there is a change in the colour of the medium due to acid production, what colour indicates that an acid is produced?

A

Yellow

65
Q

Which test is used to identify S species that consist of clumping factors and Protein A?

A

Staphylococcus Agglutination Test

66
Q

What is the function of Protein A?

A

It is used to prevent opsonization and phagocytosis of the bacteria by attaching on to IgG

67
Q

What is the reagent use for the Staphyl agglutination test?

A

Staphaurex reagent

68
Q

Explain the mechanism of action of the Staphy Agglutination Test?

A
  • Staphaurex reagent consists of latex particles that have fibrinogen and IgG
  • When the reagent is placed with S. aureus suspension then agglutination occurs
  • Protein A to IgG
  • Coagulase to Fibrinogen
69
Q

+ Staphy Agglutination Test

- Staphy Agglutination Test

A

+ clump formation with cleaning of milky background

  • no clump formation with the milky background
70
Q

Which bacteria are able to produce indole?

A

Hemophilius influenzae
E. coli
Proteus

71
Q

By what input is needed in order to produce indole?

A

Tryptophan

72
Q

What is the function of indole?

A

Formation of

  • biofilm
  • spores
  • drug resistance
  • virulence
73
Q

+ indole production

A

Change of colour to dark red

74
Q

What does the citrate utilisation test entail?

A

It tests the bacteria’s ability to use Na citrate as a source of carbon

75
Q

Which bacteria uses citrate as a source of carbon?

A

Kleibsella pneumonia

76
Q

Which bacteria other than S. aureus are + for the DNAse enzyme?

A
  • Serratia marcesens
  • Vibrio cholera
  • Aeromonas
  • Moraxella catarrhalis
77
Q

Describe the mechanism in which DNAase enzyme is indentified using a medium?

A

Add methyl green to the medium then it binds to the hydrolysed DNA, causing the medium to turn colourless around the test organism

78
Q

What is the difference between fastidous and non fastidous bacteria?

A

Fastidous bacteria require complex media that will allow for the growth of the organism.

Non fastidous bacteria can grow in any media

79
Q

Give examples of fastidous bacteria with the media they grow in?

A
  • Bordetella pertussis: Potato blood agar with Penicillin G

- Hemophilius influenzae: Blood agar with Factor X and V

80
Q

What is the difference between the chocolate agar and the blood agar?

A

The red blood cells in the chocolate agar are lysed by heating while in the blood agar they are not lysed

81
Q

How would one use the flagella test to indentify the bacteria?

A
  1. Presence or absence of flagella
  2. Number of flagella present
  3. Location of the flagella
82
Q

Give an example of a peritrichous bacteria? Peritrichous bacteria has more than one flagella, located around the the microrganism

A

Escherichia coli

83
Q

Give an example of a polar bacteria?

Polar bacteria have a single flagella located at one end tip of the bacteria

A

Pseudomonas aeruginosa

84
Q

How would you differentiate a + motile test from a - motile test?

A

+ motile test, the bacteria will have spread or moved from the site of inoculation
- motile test, the bacteria will remain at the site of inoculation

85
Q

What does the urea hydrolysis test entail?

A

Test the ability of an enzyme to produce the enzyme urease. So that the urease enzyme breaks down urea to CO2 and Ammonia

86
Q

Postive urea hydrolysis test: +

A

Change of colour of medium from light orange to magenta

87
Q

What pH shift occurs in the urea test?

A

Since there is production of ammonia ,the pH shifts from 6.8 to 8.1

88
Q

Since there are a lot of species of Hemophilius? How would one differentiate them?

A

For H. influenzae, there is growth around the XV disks meaning that it requires both XV

For H. parainfluenzae, there is growht around the XV and V disks meaning that it requires V only

For other Hemophilus spp there is growth over the entire media meaning it does not require XV, X or V for growth.

89
Q

What is a + citrate sodium utilitisation test?

A

Change of bromthymol blue indicator from green to blue

Medical Microbiology I (6 decks)

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