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MacConkey Agar is used to isolate and differentiate which type of bacteria
How is MacConckey both selective and differential?
- It is selective due to bile salt only allowing the growth of gram (-) bacteria and inhibiting gram (+)
- It is differential due to the lactose. Pink growth ferments lactose (possible coliform) and colorless growth does not ferment lactose (noncoliform)
What sugar is used in MacConkey Agar?
Name the 4 test that give presumptive indication of coliform bacteria
- LTB/ Multiple Tube Fermentation
- Brillant green lactose bile
- Endo Agar
Why is bile salt aded to MacConkey Agar?
It makes it differential, only allowing growth of gram (-) bacteria
At a pH less then 6.8 is what color? A pH above 6.8 is what color?
- pH <6.8 is yellow (Acidic)
- pH >6.8 is hot pink (Basic/Alkaline)
If an organism grows on MacConkey Agar but remains colorless, what can you conclude about this organism?
- The colorless growth is a gram (-) bacteria but is a non lactose fermenter
What is hemolysin?
Its an enzyme the lyses RBC
What does hemolysin do? What type of organism produces it?
It is produced Streptococci and they lyse RBC
What does alpha hemolysis look like on blood agar?
INcomplete destruction of RBC causes the greenish discoloration
What does beta hemolysis look like on a blood agar plate?
- Complete destruction of RBC
- A clear zone
What pathogen is an example of beta hemolysis? What disease does it cause?
- Streptococcus pyogens
- Cause pharyngitis and scarlet fever
What does "normal flora" mean?
That an organism is indigenous or living in its natural habitat
What does oxygen labile mean?
It means that is can be deactivated by O2
How is MSA(Mannitol Salt Agar) selective?
It contains a high [salt] of 7.9%
How is MSA(Mannitol Salt Agar) differential?
- It differentiates between pathogenic and non pathogenic organisms
- Non pathogenic cannot ferment mannitol
- Pathogenic can ferment mannitol
MSA favors organisms that can tolerate what?
What species does MSA differentiate?
Staphylococci - which will ferment mannitol, from less pathogenic species that DO NOT
What is the pH indicator in MSA
What test is this? What does it determine?
- This is a MSA agar plate
- Differentiate pathogenic vs non pathogenic
- Yellow= mannitol fermenters
- Pink= Non mannitol fermenters
Give two examples of pathogenic and non pathogenic organisms and their fermentation results
- Staph. aures- Pathogenic; (+) fermenter
- Staph. epidermis- Nonpatho; (-) fermenter
Name the two types of hemolysin produced by streptococci. Which one is oxygen stable? Which one is oxygen labile?
- Streptolysin O - Oxygen labile
- Streptolysin S- Oxygen stable
What is the name of the NonLancefield group and organism that produce alpha hemolysis?
- Viridans group
- Strep. pneumoniae
What are the two groups the produce beta hemolysis and examples of each.
- Group A Strep (GAS)- Strep. Pyogens
- Group B Strep (GBS)- Strep agalactiae
Which bacteria is part of the normal flora of the gut and the female urogenital tract? What does it cause?
- Strep. agalactiae
- Meningitis during baby delivery
Which organism contributes to tooth decay? What is it resistant to?
- Strep. mutans
- Forms biofilms
- Resistant to optochin
What does Bile Esculin Azide Agar detect?
- Enterococcus faecalis
- Gram(+) cocci
How is Bile Esculin Azide Agar selective?
- Contains oxgall (Bile from an ox)
- Inhibits all gram(+) growth EXCEPT Enterococci
- Contains sodium azide
- Inhibits growth of Gram(-) organisms
What is the indicator in Bile Esculin Azide Agar?
Iron is the indicator
How does Bile Esculin Azide Agar work?
- Esculin can be hydrolyzed under acidic conditions to glucose+esculetin, but bile prevents this from happening, except for enterococci
- Esculetin reacts with iron turning medium dark brown
What indicates a positive test for Bile Esculine Azide Agar?
More then 50% of the tube dark brown within 48 hours
What test is used for Staphylococcus ID?
Mannitol Salt Agar
What are common characteristics of Stahpylococcus
- Gram (+)
- Salt tolerant
- Found in skin and nasal cavity
What does a yellow MSA test mean? How can you be sure?
- Presumptive for Staph. aureus
- To be sure organism is Staph aureus you can perform 3 other tests: Catalase, Blood Agar(B-hemolysis), coagulase. (all 3 must be positive)
What is the CAMP test used to differentiate?
Group B Streptococcus (Streptococcus agalactiae) from other Strep species
How are different species of Streptococcus differentiated?
What organism produces the CAMP factor?
How is the CAMP factor made?
Hemolytic factor of Strep. agalactiae acts with beta hemolysin of staph. aureus creating the camp factor
What is bacitracin and where can you find it commercially?
Bacitracin is an antibiotic found in neosporin
What are the 4 components of blood?
- WBC (leukocytes)
What is the responsibility of RBCs?
What is the responsibility of WBCs?
Works for the immune system
- Liquid portion of the blood
- CONTAINS clotting factors
Blood plasma WITHOUT clotting factors
Coagulase Test tests for what? Is used for to confirm what?
- To test for the enzyme coagulase that staph aureus produces
- Confirms the presence of Staph aureus
Why is Staph. aureus resistant to immune system and antimicrobials?
- Due to the coagulase enzyme
- Works with fibrinogen to form a protective fibrin(protein) barrier around the bacterial celel
- Protects it from phagocytosis
What is the main ingredient in the Coagulase test?