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
How is blood agar differential?
differentiates among Streptococcus members by their hemolytic ability
Sheep blood provides RBCs (and Hgb) for streptolysin to hemolyze
Results for blood agar
Alpha hemolysis
-partial destruction of RBCs
-green halo
- S. viridian displays alpha hemolysis
Beta hemolysis
-FULL destruction of RBCs
-Clear halo
Gamma hemolysis
-NO hemolysis
-NO change in media
Bacitran susceptibility and resistance
differential media that differentiates between resistant Staph. and susceptible Micrococcus
Uses bacitran produced by Bacillus licheniformis
Results of Bacitran S&R
Zone of inhibition indicates bacitracin susceptibility
Staph. aureus is a mannitol fermenter and has bacitracin resistance
