More Agar & Bacteria Susceptibility Flashcards
What are lysins?
Lysins are poison. Hemolysins destroy blood.
Examples of lysins
Hemolysins, Streptolysins, Streptolysin O, and Streptolysin S
Hemolysin
exotoxins produced by several species of gram (+) cocci, which are able to destroy RBCs and hemoglobin
Streptolysins
Hemolysins produced by Streptococci
Type O & S
Streptolysin O
oxygen labile and expresses max activity under anaerobic conditions
Streptolysin S
oxygen stable & responsible for the hemolytic zones around streptococcal colonies growing on the surface
Streak & Stab Technique
STREAK - allows isolation of colonies
STABS - encourage streptolysin activity bc of reduced oxygen concentration in the subsurface environment
2 types of agar used to identify gram (+) microbes
Mannitol Salts Agar & Blood Agar
Mannitol Salts Agar ID…
Staphylococcus
Blood Agar ID…
Streptococcus
Mannitol Salts Agar are…
selective & differential
How are mannitol salts agar selective?
select for gram (+) staphylococci
- suppresses growth of gram (-)
-NaCl inhibits growth of gram (-) and most gram (+) other than Staphylococci
How are mannitol salts agar differential?
differentiates btw pathogen and non-pathogenic Staphylococci
Mannitol- Sugar substrate for fermentation; pathogenic Staph. can ferment mannitol
Phenol red- pH indicator; turns yellow (usually pathogenic) when acidic and red when neutral
Results for MSA?
Gram (-) will not grow
Staphylococcus mannitol fermenters (pathogenic) grow with yellow halow
Staph. non-manitol fermenters (non-pathogenic) grow w no color change
most non-Staph gram (+) will not grow on this media
Blood agar is…
Differential
