Bacterial Culture Media

Question 1

Media is classified based on?

Answer 1

• Chemical constituents
• Physical nature - liquid, semi solid, solid
• Function - supportive, enriched, selective, differential

Question 2

Chemical constituents categories

Answer 2

Defined - All conc’ns + components known

Complex - Ingredients + conc’ns unknown

Question 3

Media types - diff functions

Answer 3

Supportive - supports any organisms e.g. soy agar

Enriched - general purpose media enriched with blood; increase num of microbes to detectable levels
—heat to release nutrients from blood

Selective - allows growth of particular organisms and inhibits growth of others

Differential - diff groups based on biological characteristics

Question 4

Examples of selective media

Answer 4

• MacConkey agae has Bile salts - allow certain microorganisms to grow e.g. E coli
• eosin Y and methylene blue - inhibits gram +ve bacteria
• Bile salts and crystal violet - inhibits gram +ve bacteria
• 7.5% NaCl - selects Staph spp.

Question 5

Examples of differential media

Answer 5

Blood agar - haemolytic vs non-haemolytic
—> (alpha haemolysis - strep haemolysis,
beta haemolysis - strep viridians,
gamma haemolysis - enterococcus faecalis)

MacConkey agar (selective+differentiating) - lactose fermenter - E coli (red) vs non-fermenter (pale) - salmonella

Question 6

Anaerobe cultures requirements

Answer 6

Culturing anaerobes requires:

• -appropriate media = low oxidation-reduction potential
• -substrates obtained by microorganisms in their natural habitat

Question 7

Anaerobic culture - specimen

Answer 7

Throat, rectal swabs, urine, bronch washes, cervico-vaginal mucosal swabs, sputum

Question 8

Liquid media - purpose

Answer 8

Liquid media provide greater sensitivity for the isolation of small numbers of microorganisms

Question 9

Growth in liquid media also can be ordinarily quantitated (T/F)

Answer 9

False

Question 10

Bacteria grown in liquid cultures often form colloidal suspensions (T/F)

Answer 10

True

Question 11

Examples of liquid media

Answer 11

Peptone water, nutrient broth, glucose broth, brain-heart infusion broth, alkaline peptone water, selenite F broth, Tetrathionate broth, Robertson’s cooked meat broth

Question 12

Peptone water use

Answer 12

Sugar fermentation test, indole test

Question 13

Nutrient broth use

Answer 13

Routine culture

Question 14

Glucose broth use

Answer 14

Blood culture, Fastidious organisms e.g. Streptococci

Question 15

BHI broth use

Answer 15

Whole blood, bone marrow, body fluid culture

Question 16

Alkaline peptone water use

Answer 16

Enrichment media - Vibrio

Question 17

Selenite F Broth use

Answer 17

Enrichment media - Salmonella + shigella

Specimen: feces

Question 18

Tetrathionate Broth use

Answer 18

Salmonella culture

Specimen: feces

Question 19

Robertson’s cooked meat broth use

Answer 19

Anaerobic bacterial culture

Question 20

Solidifying agent in culture media

Answer 20

Agar is used as a solidifying agent in most culture media.

Question 21

Solid media can be altered via agar in what way?

Answer 21

By varying the concentration of agar, it is possible to make the medium solid or semisolid.

Question 22

Solid media vs liquid media

Solid media function

Answer 22

Solid media

• less sensitive than liquid media,
• isolated colonies that can be quantified and identified

Question 23

Examples of solid media

Answer 23

Nutrient agar, MacConkey agar, blood agar, Chocolate agar, Deoxycholate citrate agar, Thiosulfate citrate bile salt sucrose agar, Loeffler’s serum slope, Lowenstein-Jensen medium

Question 24

Nutrient agar use

Answer 24

Routine culture

Question 25

What solid media cultures gram negative bacteria e.g. E coli?

Answer 25

MacConkey agar

Question 26

Blood agar use

Answer 26

Routine culture, culture of fastidious organisms e.g. Streptococci

Question 27

What solid media cultures H influenzae and Neisseria?

Answer 27

Chocolate agar

Question 28

What solid media cultures Vibrio cholerae?

Answer 28

Thiosulfate citrate bile salt sucrose agar

Question 29

Solid media responsible for culture of Salmonella spp and Shigella spp

Answer 29

Deoxycholate citrate agar

Question 30

Solid media responsible for culture of Corynebacterium diptheriae

Answer 30

Loeffler’s serum slope

Question 31

Solid media responsible for culture of Mycobacterium tuberculosis

Answer 31

Lowenstein-Jensen medium

Question 32

Selective media examples

Answer 32

Mannitol salt agar, 
Thayer-Martin medium, 
MacConkey agar medium, 
Thiosulfate citrate bile salt sucrose agar, 
Charcoal yeast extract
Lowenstein Jensen media
Sabouraud's dextrose agar

Question 33

Selective media that

• inhibits streptococcus spp and
• facilitates growth of staphylococcus spp

Answer 33

Mannitol salt agar

Question 34

Selective media that

• inhibits gram +ve cocci and
• facilitates growth of Neisseria spp

Answer 34

Thayer-Martin medium

Question 35

Selective media that

• inhibits gram positive cocci and
• tests lactose fermentation

Answer 35

MacConkey agar medium

Question 36

Selective media that

• inhibits enteric bacilli and
• tests sucrose fermentation

Answer 36

Thiosulfate citrate bile salt sucrose agar

Question 37

Selective media that

• inhibits gram +ve cocci and
• facilitates growth of Legionella spp

Answer 37

Charcoal yeast extract

Question 38

Selective media that

• inhibits cocci and
• facilitates growth of Mycobacterium spp

Answer 38

Lowenstein Jensen media

Question 39

Selective media that

• inhibits most bacteria and
• facilitates growth of most fungi

Answer 39

Sabouraud’s dextrose agar

Question 40

Which of the three tests conducted in this identification process did not require the use of an incubator?

• Coagulase test
• Catalase test
• Novobiocin sensitivity test
• Mannitol salt agar plate

Answer 40

Catalase test