View
63
Download
0
Category
Preview:
Citation preview
STAPHYLOCOCCI
Mrs. Jincy EaliasM.Sc. (N)Asst. Professor
Mr. Binu BabuMBA, M.Sc. (N)Asst. Professor
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.
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
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
S. Aureus Morphology
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
Biochemical properties• Produces many virulence factors. i.e
production of enzymes and toxins
Virulence factors of S. aureusEnzymes:• 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
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
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.
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
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 stainingCultureCoagulase test
Gram stainingThe 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.
Coagulase test1 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.
Treatment
• 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
Thank You
Recommended