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Microbiology > Quiz: MacConkey, etc., > Flashcards

Quiz: MacConkey, etc., Flashcards

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1
Q

Mannitol Salts Agar (MSA)

purpose?

A

Is used for isolation and differentiation of Staphylococcus aureus

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2
Q

Mannitol Salts Agar (MSA)

differential and/or selective ingredients

A

Mannitol provides the substrate for fermentation and makes the medium differential

Sodium chloride makes the medium selective because its concentration is high enough to dehydrate and kill most bacteria

Phenol red indicates whether fermentation has taken place by changing color as the pH changes.

Phenol red is yellow below pH 6.8, red at pH 7.4 to 8.4, and pink at pH 8.4 and above.

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3
Q

Mannitol Salts Agar (MSA)

Working principles/mechanisms

A

Staphylococci thrive in the medium, largely because of their adaptation to salty habitats such as human skin

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4
Q

Mannitol Salts Agar (MSA)

Expected results

A

Most staphylococci are able to grow on MSA but do not ferment the mannitol, so the growth appears pink or red and the medium remains unchanged.

Staphylococcus aureus ferments the mannitol, which produces acids and lowers the pH of the medium. Result is bright yellow colonies usually surrounded by a yellow halo

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5
Q

Mannitol Salts Agar (MSA)

poor growth or no growth

A

Organism is inhibited by NaCl (sodium chloride)

Not Staphylococcus

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6
Q

Mannitol Salts Agar (MSA)

good growth

A

Organism is not inhibited by NaCl

Staphylococcus

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7
Q

Mannitol Salts Agar (MSA)

Yellow growth or halo

A

Organism produces acid from mannitol fermentation

Possible pathogenic
Staphylococcus aureus

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8
Q

Mannitol Salts Agar (MSA)

Red growth no halo

A

Organism does not ferment mannitol. No reaction

Staphylococcus other than S. aureus

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9
Q

MacConkey Agar (MAC)

purpose

A

Is used to isolate and differentiate members of the Enterobacteriaceae based on the ability to ferment lactose

Is a selective and differential medium

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10
Q

MacConkey Agar (MAC)

differential and/or selective ingredients

A

Bile salts and crystal violet: inhibit growth of Gram-positive bacteria

Neutral red dye: pH indicator that is colorless above a pH of 6.8 and red at a pH less than 6.8

Acid accumulating from lactose fermentation turns the dye red

Contains:
lactose
bile salts
neutral red
crystal violet

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11
Q

MacConkey Agar (MAC)

working principles/mechanisms

A

Bile salts and crystal violet: inhibit growth of Gram-positive bacteria

Acid accumulating from lactose fermentation turns the dye red

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12
Q

MacConkey Agar (MAC)

expected results

A

Lactose fermenters turn a shade of red.

Lactose non-fermenters retain their normal color or the color of the medium

Formulations without crystal violet allow growth of Enterococcus and some species of Staphylococcus, which ferment the lactose and appear pink on the medium

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13
Q

Eosin Methylene Blue Agar (EMB)

purpose

A

Used for the isolation of fecal coliforms

A complex (chemically undefined), selective, and differential medium)

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14
Q

Eosin Methylene Blue Agar (EMB)

differential and/or selective ingredients

A

Contains:
-Peptone: provides a complex mixture of carbon, nitrogen, and other nutritional components

-Lactose: supports coliforms such as E. coli

-Sucrose: encourage growth of enteric bacteria and to differentiate them based on color reactions created when combined with the dyes; supports pathogens such as Proteus or Salmonella

-Dyes Eosin Y and Methylene Blue

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15
Q

Eosin Methylene Blue Agar (EMB)

working principles/mechanisms

A

Purpose of the dyes is (1) they inhibit the growth of Gram-positive organisms and (2) they react with vigorous lactose fermenters and (in the acidic environment) turn the growth dark purple or black

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16
Q

Eosin Methylene Blue Agar (EMB)

expected results

A

Dark growth is typical of E. coli and is accompanied by a metallic sheen

Other less aggressive lactose fermenters such as Enterobacter or Klebsiella species produce colonies that can range from pink to dark purple on the medium

Non fermenters and sucrose fermenters typically retain their normal color or take on the coloration of the medium

17
Q

Eosin Methylene Blue Agar (EMB)

poor growth or no growth

A

Organism is inhibited by eosin and methylene blue

Gram-positive

18
Q

Eosin Methylene Blue Agar (EMB)

good growth

A

Organism is not inhibited by eosin and methylene blue

Gram-negative

19
Q

Eosin Methylene Blue Agar (EMB)

growth is pink and mucoid

A

Organism ferments lactose with little acid production

Possible coliform

20
Q

Eosin Methylene Blue Agar (EMB)

Growth is “dark” (purple to black, with or without green metallic sheen)

A

Organism ferments lactose and/or sucrose with acid production

Probable coliform

21
Q

Eosin Methylene Blue Agar (EMB)

Growth is “colorless” (no pink, purple, or metallic sheen)

A

Organism does not ferment lactose or sucrose, no reaction

Noncoliform

22
Q

Blood Agar

Purpose

A

Is used for isolation and cultivation of many types of fastidious bacteria

Also used to differentiate bacteria based on their hemolytic characteristics, especially within the genera Streptococcus, Enterococcus, and Aerococcus

23
Q

Blood Agar

differential and/or selective ingredients

A
24
Q

Blood Agar

working principles/mechanisms

A

Several species of Gram-positive cocci produce exotoxins calle hemolysins, which are able to destroy red blood cells and hemoglobin.

Blood Agar, allows differentiation of bacteria based on their ability to hemolyze RBCs

25
Q

Blood Agar

Expected results

A

B-hemolysis: the complete destruction of RBCs and hemoglobin, results in a clearing of the medium around the colonies

a-hemolysis: is the partial destruction of RBCs and produces as greenish discoloration of the agar around the colonies

y-hemolysis: non-hemolysis and appears as simple growth with no change to the medium

26
Q

Blood Agar

Clearing around growth

A

Organism hemolyzes RBCs completely

B-hemolysis

27
Q

Blood Agar

Greening around growth

A

Organism hemolyzes RBCs partially

a-hemolysis

28
Q

Blood Agar

No change in the medium

A

Organism does not hemolyze RBs

no (y) hemolysis

Microbiology (17 decks)

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