Isolation of Staphylococcus aureus

and Streptococcus Lab #12

Medgar Evers CollegeProf. Santos

Exercise 70 week 2

• You should have from last week, three tubes of Staphylococcus broth with S.aureus from three sources; a control, a fomite, and your nose.• This week, you will attempt to isolate the colonies by plating them on

solid media. You will use two media; MSA (MANNITOL SALT AGAR) and SM110 (STAPHYLOCOCCUS MEDIUM 110)

MSA

• This medium containsa. Mannitolb. 7.5 % sodium chloridec. Phenol red indicator S.aureus ferments mannitol and will turn the medium from red to yellow due to the formation of acid. The other strains of Staph do not ferment mannitol and will appear red.

MSA

SM110

• This medium contains mannitol, 7.5 % NaCl but lacks the phenol red so the medium doesn’t change to yellow. The advantage of using this medium is that it allows you to see the different colony colors produced by the different Staph strains.

SM110

Exercise 71

• This week you will examine your blood agar plate from last week, and differentiate between alpha and beta hemolysis.• Alpha hemolysis is partial breakdown of red blood cells and beta

hemolysis is total breakdown of red blood cells. • Greenish colonies are indicative of alpha hemolysis and clear colonies

are indicative of beta hemolysis.• This week you will pick the colonies and make sub-cultures for next

week. Use trypticase soy broth for this experiment.

Alpha hemolysis

Beta hemolysis

Lab 72; week 1

• Isolating pathogenic gram – organisms.

• You will be given a sample of either Salmonella or Shigella to isolate.

• Streak a plate of MacConkey and a plate of Hektoen Enteric agar with the mixture provided.

• These 2 media inhibit the growth of gram + bacteria.