LAB : Week 13

used to differentiate bacteria based on the hemolysis of blood

- a differential media with various nutrients and 5% sheep blood
- can be used to cultivate the normal flora in the throat to determine if bacteria can hemolyze RBC's by using exotoxins called Hemolysins to breakdown RBC's

complete lysis of the RBC's by the exotoxin beta-hemolysin
- results in a clear zone around the growth

partial lysis of the RBC's by the exotoxin alpha-hemolysin
-results in green color around growth and partial clearing

no hemolysis and bacteria will grow normally on the blood agar plate

grouping of bacteria based on the M protein that helps bacteria avoid phagocytosis (Group A,B, D)

- Group A Strep and can cause strep throat (pharyngitis)
- beta-hemolytic

- Group B Strep and can cause problems with new borns
- beta-hemolytic

- Group D Strep that lives in the GI tract
- some strains are resistant to antibiotics
- gamma-hemolytic

a strain of enterococcus faecalis that is resistant to antibiotics
- nosocomial infection

- causes dental caries by digesting sucrose into dextran (glucose) which causes acid production to cause dental caries
- alpha-hemolytic

- causes pneumonia and produces a capsule that is anti-phagocytic so that the bacteria can avoid phagocytosis
- alpha-hemolytic

- has Bacitracin (antibiotic)
- Streptococcus pyogenes (strep throat) is sensitive to the bacitracin and will not grow in the presence of it
- used to detect streptococcus pyogenes

- has Optochin (antibiotic)
- only bacteria sensitive to the Optochin is streptococcus pneumoniae

- test performed to confirm the presence of Group B Streptococcus agalactiae
- differentiates between Group A and B

purpose is to select for staphylococcus and to presumptively identify staphylococcus aureus

- found on 100% of all humans and 90% on the skin flora
- non-pathogenic
- non-fermenter on mannitol on the plate

- found on 30% of humans
- pathogenic
- mannitol fermenter and only this type can ferment

- peptones : general growth (alkaline products)
- mannitol : fermentable sugar (acidic products)
- phenol red : pH indicator
- sodium chloride : 7.5% high concentration to inhibit the growth of microbes that can't tolerate the high amounts of salt

- purpose to determine if the bacteria produce coagulase
- can be used to confirm the presence of staphylococcus aureus from the MSA plate since pathogenic strains produce coagulase

- rabbit plasma used since has clotting factor fibrinogen
- if bacteria produce coagulase then it will use the fibrinogen to form fibrin clots
- fibrin blood clots can then surround the bacteria to protect the bacteria from phagocytosis