This document discusses Staphylococcus, including S. aureus. It describes the morphology and cultural characteristics of S. aureus, noting it is a gram-positive coccus that grows in clusters and produces golden yellow pigment on blood agar. S. aureus can cause a variety of infections through production of enzymes and toxins. Laboratory diagnosis involves gram staining, culturing, and coagulase testing of samples. Treatment often involves cephalosporins due to high resistance of S. aureus to penicillin.

1. STAPHYLOCOCCI
Mrs. Jincy Ealias
M.Sc. (N)
Asst. Professor
Mr. Binu Babu
MBA, M.Sc. (N)
Asst. Professor

2. Staphylococci
Staphylococcus is a gram positive cocci. It is frequently
involved in nosocomial and opportunistic infections.
Different species of Staphylococcus are;
• S. aureus – lives in respiratory tract and skin.
• S. epidermidis – lives on skin and mucous
membranes.
• S. hominis – lives around sweat glands.
• S. capitis – live on scalp, face, external ear.
• S. saprophyticus – lives on skin, intestine, vagina.

3. General Characteristics of
the Staphylococci
• Common inhabitant of the skin and mucous
membranes
• Spherical cells arranged in irregular clusters
• Gram-positive
• Lack spores and flagella
• May have capsules

4. Staphylococcus aureus
Morphology
• Non motile and non spore forming
• Gram positive cocci
• Size is 0.7 to 1.2 µm in diameter
• Irregular clusters that resemble cluster
of grapes

5. S. Aureus Morphology

6. Cultural characteristics
• Grows in large, round, colonies.
• Optimum temperature of 37oC
• Facultative anaerobe
• Withstands high salt, extremes in pH, and high
temperatures
• Isolation is best done in blood agar. Produce a
characteristic golden yellow carotenoid pigment. On
blood agar colonies are usually surrounded by a zone of
clear hemolysis.
zone of hemolysis

7. Biochemical properties
• Produces many virulence factors. i.e
production of enzymes and toxins

8. Virulence factors of S. aureus
Enzymes:
• Coagulase – coagulates plasma and blood.
• Hyaluronidase – digests connective tissue
• Staphylokinase – digests blood clots
• DNase – digests DNA
• Lipases – digest oils; enhances colonization
on skin
• Penicillinase – inactivates penicillin

9. Toxins:
• Hemolysins – lyse red blood cells
• Leukocidin – lyses neutrophils and
macrophages
• Enterotoxin – induce gastrointestinal
distress
• Exfoliative toxin – separates the epidermis
from the dermis
• Toxic shock syndrome toxin (TSST) –
induces fever, vomiting, shock, systemic
organ damage

10. Pathogenesis
• Present in most environments frequented
by humans.
• Carriage rate for healthy adults is 20-60%.
• Carriage is mostly in anterior nares, skin,
nasopharynx and intestine
• Predisposition to infection include: poor
hygiene and nutrition, tissue injury,
preexisting primary infection, diabetes,
immunodeficiency.

11. Staphylococcal Disease
• Localized cutaneous infections – invade skin
through wounds, follicles, or glands.
• Systemic infections
– Osteomyelitis – bone infection
– Bacteremia – transmission of bacteria from one infected
site to another. Eg: endocarditis
• Toxigenic disease
– Food intoxication – ingestion of heat stable enterotoxins;
gastrointestinal distress
– Staphylococcal scalded skin syndrome – toxin induces
bright red flush, blisters, then desquamation of the
epidermis
– Toxic shock syndrome – toxemia leading to shock and
organ failure

13. Laboratory diagnosis
• Staphylococcus aureus is frequently isolated
from samples such as pus, tissue exudates,
sputum, urine, and blood.
• Different methods for laboratory diagnosis of
Staphylococcus aureus are;
Gram staining
Culture
Coagulase test

14. Gram staining
The diagnosis of staphylococcus aureus is
suggested by the finding of gram positive bacteria in
clumps in the sample.
Culture
10 ml venous blood is inoculated into 50 ml
glucose broth. Identification of staphylococcus
aureus depends on its colony characteristics in
culture media such as blood agar. The characteristics
haemolysis and yellow pigmentation suggest S.
aureus.

15. Coagulase test
1 ml of overnight broth suspension from agar
plate is mixed with 1 ml of 10% dilution of human
plasma (any fresh plasma). The mixture is incubated
at 37oC for 3-6 hrs. Check for presence of clot. If clot
appears it is positive and if no clot it is negative.

17. Treatment
• 95% S. aureus have penicillinase and are
resistant to penicillin and ampicillin.
Cephalosporins are the drug of choice in
case of penicillin resistance.

18. Prevention of Staphylococcal Infections
• Universal precautions by healthcare
providers to prevent nosocomial infections
• Hygiene and cleansing

19. Thank You