Specialized Media/Carbohydrate Metabolism
Terms
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- enriched media
- basal growth media with one or more growth factors added (enrichments)
- What are some growth factors?
- blood, carbs, amino acids, vitamins, and nacl
- what characterizes fastidious bacteria
- the need for additional nutrients in their media/environment
-
what is an auxotroph?
for e.g., -
it is derived from a prototroph which grows on a basal media.
-a bacterium which has mutated and developed a specific growth requirement that it previously synthesized itself
e.g. Streptococcus - halophile
-
salt-loving bacterium;
e.g., Vibrionolipherocous - enrichment media
-
-suppresses normal flora while enhancing pathogen growth
-usually for stool specimens - What does a selective media do?
- selects for the growth of some bacteria while inhibiting the growth of others.
- Some general agents of a Selective media
- Antibiotics, Dyes, Chemicals, pH changes
- What is the purpose of a selective media?
- to better identify a bacterium
- What is the purpose of an Enteric Media?
- to isolate pathogens of the intestine.
- What are ALL enteric media selective for?
- Gram negative bacilli
-
What does a Low selectivity Enteric media ALLOW to grow?
Moderately selective?
HIghly selective? -
-All GNB, whether pathogen or not.
-Moderately inhibits some normal flora.
-Highly inhibits almost all normal flora
and sometimes the pathogen itself too! - What is the purpose of a differential media?
- to differentiate between bacteria, based on some charactistic which is usually based upon a biochemical reaction.
- What kind of media are pH indicators in, and what do they do?
- in DIFFERENTIAL; they register the difference between bacteria.
- what are the three main ways for bacteria to produce energy?
-
-Fermentation
-Aerobic respiration
-Anaerobic respiration -
catabolism
anabolism -
break down of molecules into energy
buildup of molecules using energy -
how to report hemolysis:
gamma
alpha
beta -
gamma - no hemolysis
alpha - incomplete hemolysis; green-brown discoloration
beta - complete hemolysis; clear, colorless zone around colony - why stab the plate for hemolysis?
- so if colonies being streaked are oxygen labile they will have the correct atmosohere to grow in
- most common types of enrichment media:
-
-selenite
-GN broth
-tetrathionate - additives that make a medium selective:
- dyes, bile salts, pH adjustments, antibiotics
-
CA stands for
and does what -
chocolate agar
supports growth of fastidious bacteria -
what plates are low selectivity?
how do they work? -
LEMB and McConkey's.
allow all gnb to grow; do not select for enteric pathogens. -
What plates are moderately selective?
How do they work? -
-xld
-ss
-he
they select for GNB, and contain chemicals that inhibit growth of normal gnb flora. -
what plates are highly selective?
how do they work? -
bismuth sulfite agar
brillian green agar
contain chemicals which inhibit virtually all enteric non-pathogens.