Mrs. Jincy Ealias
Mr. Binu Babu
MBA, M.Sc. (N)
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
• S. hominis – lives around sweat glands.
• S. capitis – live on scalp, face, external ear.
• S. saprophyticus – lives on skin, intestine, vagina.
General Characteristics of
• Common inhabitant of the skin and mucous
• Spherical cells arranged in irregular clusters
• Lack spores and flagella
• May have capsules
• Non motile and non spore forming
• Gram positive cocci
• Size is 0.7 to 1.2 µm in diameter
• Irregular clusters that resemble cluster
• Grows in large, round, colonies.
• Optimum temperature of 37oC
• Facultative anaerobe
• Withstands high salt, extremes in pH, and high
• 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
zone of hemolysis
• Produces many virulence factors. i.e
production of enzymes and toxins
Virulence factors of S. aureus
• Coagulase – coagulates plasma and blood.
• Hyaluronidase – digests connective tissue
• Staphylokinase – digests blood clots
• DNase – digests DNA
• Lipases – digest oils; enhances colonization
• Penicillinase – inactivates penicillin
• Hemolysins – lyse red blood cells
• Leukocidin – lyses neutrophils and
• Enterotoxin – induce gastrointestinal
• Exfoliative toxin – separates the epidermis
from the dermis
• Toxic shock syndrome toxin (TSST) –
induces fever, vomiting, shock, systemic
• Present in most environments frequented
• 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,
• 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;
– Staphylococcal scalded skin syndrome – toxin induces
bright red flush, blisters, then desquamation of the
– Toxic shock syndrome – toxemia leading to shock and
• 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;
The diagnosis of staphylococcus aureus is
suggested by the finding of gram positive bacteria in
clumps in the sample.
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.
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.
• 95% S. aureus have penicillinase and are
resistant to penicillin and ampicillin.
Cephalosporins are the drug of choice in
case of penicillin resistance.
Prevention of Staphylococcal Infections
• Universal precautions by healthcare
providers to prevent nosocomial infections
• Hygiene and cleansing