LAB 2 - COLONIAL AND GRAM MORPHOLOGY, CULTURE MEDIA Flashcards
A plate is growing white, opaque colonies, non-hemolytic on a BAP. The sample was taken from
a patient with a UTI. What organism is of most concern? Are there any additional tests that
must be done? If so, what are they and what are the expected results?
a. What would you report if it is the organism of concern?
- Staphylococcus saprophyticus
- Gram stain (g+c, clps) → catalase (+) → coagulase (-) → DNAse → (-) novobiocin (R)
What makes a media differential? What makes a media selective? What makes a media
enriched?
Selective media: Inhibitory reagents (dyes, chemicals, antimicrobials) inhibits growth of certain bacteria
Enriched media: Serum, blood, yeast added to grow fastidious bacteria
BAP:
1. Components
(include inhibitory
agents, indicators,
etc.)
2. Function of
major
components
3. Type of media (i.e..
Selective,
differential,
enriched, etc.)
4. Examples of
organisms that
grow on this
media
- Defibrinated sheep blood (5%) on TSB agar
- Bacterial growth
- Enriched, non-selective, differential (hemolysis)
- Staphylococcus, streptococcus, almost everything…
TSB - Tryptic Soy Broth
CAP:
1. Components
(include inhibitory
agents, indicators,
etc.)
2. Function of
major
components
3. Type of media (i.e..
Selective,
differential,
enriched, etc.)
4. Examples of
organisms that
grow on this
media
- Heated sheep blood (5%) on TSB agar, yeast extract, hemin (X factor), NAD (V factor)
- Growth of fastidious bacteria; heated BAP destroys NADase and releases hemoglobin for growth
- Enriched, non-selective, differential (hemolysis)
- Haemophilus influenzae
TSB - Tryptic Soy Broth
NAD - Nicotinamide adenine dinucleotide
Colisin-Nalidixic Acid
Agar (CNA):
1. Components
(include inhibitory
agents, indicators,
etc.)
2. Function of
major
components
3. Type of media (i.e..
Selective,
differential,
enriched, etc.)
4. Examples of
organisms that
grow on this
media
- Antibiotics (colisin+nalidixic acid), dyes chemical inhibitors added to nutrient/ enriched media
- Inhibits growth of normal flora
- Selective
- Gram positive bacteria
MAC:
1. Components
(include inhibitory
agents, indicators,
etc.)
2. Function of
major
components
3. Type of media (i.e..
Selective,
differential,
enriched, etc.)
4. Examples of
organisms that
grow on this
media
1-2. Peptone, proteone peptone, NaCl, lactose (substrate), neutral red (indicator), crystal violet (inhibits gram+ve), bile salts
3.
- Selective: inhibits growth of gram+ve bacteria; allows growth for Enterobacteriaceae and non-fermentative bacilli
- Differential: lactose fermenters (pk) from non-lactose fermenters (wh)
4. Enterobacteriaceae
What is an advantage of using MAC for Proteus sp.?
Inhibits Proteus sp. from spreading over the plate and other colonies
Explain alpha, beta and gamma hemolysis? What is happening to the red cells?
Alpha: incomplete hemolysis with partial breakdown of hemoglobin; partial clearing with green discoloration around colonies
Beta: complete lysis of RBC and breakdown of hemoglobin; distinct clearing around colonies
Gamma: no hemolysis
Why is it good practice to avoid streaking too close to the edge of a plate?
There are contaminants near the edge of the plate