LESSON OUTLINE #9
MICROCOCCACEAE
GENERAL CHARACTERISTICS
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Gram (+) cocci in cluster
Aerobic or facultative anaerobic
Catalase (+) except Stomatococcus
Colony characteristics: opaque, smooth, growth is butyrous
This genera includes three genus
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Micrococcus
Staphylococcus
Somatococcus
They can be differentiated as in the fallowing table:
Genera
Catalase
Mod.
Oxidase
Sensitivity
Furazolidone
Bacitracin
Micrococcus
+
+
Resistant (R)
Sensitive (S)
Staphylococcus
+
-
S
R
Stomatococcus
-
-
S
S
STAPHYLOCOCCUS
Staphylococcus (from the Greek: staphylē, "grape" and kókkos, "granule") is a genus of
Gram-positive bacteria. Under the microscope, they appear round (cocci), and form in grapelike clusters.
Staphylococcus can be differentiated from Streptococcus on basis of positive catalase test
3 medically important species of Staphylococcus are as follows:
1. S. aureus causes abscesses, pyogenic infections (endocarditis, osteomyelitis), food
poisoning, and toxic shock syndrome. It is the most important of species distinguished
from other Staphylococcus by positive coagulase test.
2. S. epidermidis may cause endocarditis. It is coagulase negative, produces glycocalyx
and sensitive to novobiocin. It is also present on inhabits skin.
3. S. saprophyticus causes urinary tract infections. It is also coagulase negative but
resistant to novobiocin.
STAPHYLOCOCCUS AUREUS:
MICROSCOPY:
Gram’s staining
CULTURAL CHARECTERS:
1. On Nutrient agar: Opaque, smooth, small, golden yellow colonies.
2. On Sheep Blood agar: Small, opaque, Beta haemolytic colonies.
3. On Tellurite lysine agar: Small, smooth, black colonies.
4. On Mannitol salt agar: ferments mannitol.. Yellow colonies (+) for Staphylococcus
aureus)
Pathogenecity: It produces many toxins which helps this bacteria to cause disease
1. Enterotoxins –toxin produced that is very potent
Laboratory Diagnosis:
1. Microscopy: Gram positive cocci in clusters.
2. Culture:
a. On Nutrient Agar Plate (NAP) : Opaque, smooth, small, golden yellow
colonies.
b. On Sheep Blood Agar Plate (sBAP): Small, opaque, Beta haemolytic colonies.
c. On Tellurite lysine agar (TLA) : Small, smooth, black colonies.
d. On Mannitol Salt Agar (MSA) : ferments mannitol.
3. Biochemical reactions:
a. Catalase Test: Catalase is an enzyme that converts H202 into water and
oxygen. Therefore when we put a colony of staphylococcus in H2O2 it gives
(+) reaction, that is bubble formation.
b. Coagulase Test: In the presence of coagulase, fibrinogen is converted to fibrin.
It can be detected by 2 methods.
i. Slide test – detects bound coagulase
ii. Tube test – detects free coagulase
c. DNAse Test: S.aureus also produces DNAse (deoxyribonuclease) which
breaks down the DNA. The test agar contains an emulsion of DNA, peptides
as a nutrient source, and methyl green dye. Bacterial colonies that secrete
DNase will hydrolyze the DNA in the medium, . This results in clearing
around the bacterial growth.
d. Oxidase Test: Bacteria that possess cytochrome C produce a dark-blue end
product when reacted with modified oxidase reagent.
4. Antibiogram: The antibiotics which can be used area. Lysostaphin
b. Bacitracin
c. Furazolidone
d. Novobiocin
5. Serology: Many readymade tests are available to detect staphylococcal infection.
6. Phage Typing
SUPPLEMENTAL READING:
Microbiology Demystified by Tom Betsy, 2005.
Foundation of Microbiology, 4th edition by Talaro, Kathleen , 2002. Chapter 7. Elements of Microbial
Nutrients
Textbook: Microbiology: introduction 10th edition: Tortora, Funk, case