Download Identification of Strep and Staph and Isolating gram

Identification of Strep and Staph
and Isolating gram – pathogens
Lab # 10
Medgar Evers College
Prof. Santos
Exercise 70
• Isolation of Staphyloccocus aureus from three sources, fomite,
nose and a given culture.
• There are some properties you need to know beforehand
– Gram positive spherical bacteria that divide in more than one plain to
form irregular clusters.
– When grown in trypticase soy agar or blood agar the colonies are 1 to 3
mm in diameter.
– The colonies may be yellow, orange or white.
– they are coagulase positive meaning they can clot serum
– they produce alpha toxin to yield a clear zone of beta hemolysis in
blood agar plate
– ferment mannitol sugar to produce acid
– Are salt tolerant.
• Know the chart of the three
different species of
Staphylococcus and their
properties.
S. aureus
S. epidermidis
S.saprophyticus
Alpha toxin
+
-
-
Mannitol
+
-
Mostly +
Coagulase
+
-
-
Biotin for growth
-
+
Not significant
Novobiocin
sensitive
sensitive
resistant
Week 1
•
•
•
•
Inoculate three tubes of Staphylococcus broth.
One from a culture of Staph
One from a fomite
One from your nose using a sterile cotton
swab!
Exercise 71
• The main objective here is to isolate
Streptococci and characterize them based on
certain properties. Pretty much you need to be
able to identify them according to Lancefield
group, A, B, C, D or none. Know the table in
your book!
• Know 2 differences between the Staphylococci
and Streptococci.
2 differences
1- Staph grows in clusters and Strep grows in
chains.
2- Streptococcus are catalase negative and
Staphylococcus are catalase positive.
Week 1
• Isolate Strep from your throat using a sterile
cotton swab and tongue depressor.
Swab the back of your throat and inoculate a
blood agar plate.