1. Staphylococcus aureus
Buga Rudolf
HTC LECTURE SERIES.
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2. Introduction
•S. aureus:
A major pathogen for humans may cause suppuration,
abscess formation, scalded skin syndrome, toxic
shock syndrome and food poisoning.
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3. Characteristics
• Facultative anaerobe
• Catalase positive
• Coagulase positive
• DNase positive
• Gram positive cocci
• Salt tolerant
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4. Microscopy
•Gram positive
cocci in clusters
(bunch of grapes)
• Non-sporing
• Non motile
• Non capsulate
• 1µm in diameter
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5. Lab Diagnosis
•Specimens: Pus swab, sputum, blood, urine, faeces,
etc.
• Gram posittve cocci
• Culture:
• Growth atmosphere: O2/ANO2 at 370 C
• Incubation: 24 hours
• Media used: Mc, BA, Mannitol Salt agar,etc.
• Cols: shinny, smooth , low convex and 1-3mm in
diameter on NA or BA
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6. Lab Diagnosis…
4. Identification tests:
• Catalase test
• Coagulase test
• DNase test (Confirmatory test)
• Typing methods:
• Plasmid profile analysis
• Pulsed-field gel electrophoresis
• Phage typing (epidemiological purpose).
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8. Antimicrobial resistance
•MRSA ( Methicillin Resistance Staph
Aureus)
•VRSA ( Vancomycin Resistance Staph
Aureus)
• NB: Limited treatment option.
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9. Pathogenesis
•Present in the nose of 30% of healthy people and
may be found on the skin
•Causes infection at sites of lowered host resistance,
e.g. damaged skin or mucous membrane
•Produce diseases by both invasiveness and toxin
production
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10. Pathogenesis…
Virulence factors:
Cytotoxins
• α-toxin: Pore-forming, and cytotoxic to many types of
cells including muscle cells
• β-toxin: Degrades sphingomyelin and toxic to many
kinds of cells, including human RBCs
• γ-toxin: Pore-forming
• η-toxin: Has detergent-like activity
• P-V leucocidin: Similar to γ-toxin in structure, kill
WBCs of many animals and associated with severe
cutaneous infections.
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11. Pathogenesis…
•Exfoliative (epidermolytic) toxins
• Proteases that bind to GM4-like glycolipids
• Split intercellular bridges in epidermis
• Cause the generalized desquamation of the
staphylococcal scalded skin syndrome
• Produced by 5-10% of S. aureus
•Toxic shock syndrome toxin-1 (TSST-1)
Super antigen, associated with fever, shock,
desquamative skin rash of toxic shock syndrome in
humans
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12. Pathogenesis…
Enterotoxins:
• Super-antigens ; Ten (10)antigens (A, B, C1,
C2, C3, D, E, G, H, and I) soluble toxins
produced by about 50% of S. aureus
• Heat-stable (1000C, 30 min.) and resistant to
the gut enzymes
•Enterotoxins are produced in carbohydrate
and protein foods
• Causing emesis, a characteristic of
staphylococcal food poisoning
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13. Pathogenesis…
Enzymes
•Coagulases: bound and free forms. (associated with
invasiveness)
•Fibrinolysin (staphylokinase): to dissolve fibrin clot.
•Catalase: to remove H2O2
•Hyaluronidase: to facilitate spread of S. aureus in
tissue
•Lipase: associated with superficial skin infection
•Nuclease: produced only by S. aureus
•Penicillinase
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14. Epidemiology
Sources of Infection:
1. Infected lesions
• Large no. of spread in pus and dried exudates
discharged from infected wounds, burns,
secondarily infected skin lesions and in sputum
• Direct contact is an important mode, but airborne
spread may occur
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15. Epidemiology…
2. Healthy carriers:
• Spread by hand-shake, handkerchiefs, clothing
and dust consisting of skin squames and cloth
fibres of healthy carriers
• Some carriers (shedders) disseminate
exceptionally large no. of cocci like that from
infected persons
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16. Epidemiology…
Areas at highest risk for severe infections:
• 1. New born nursery
• 2. ICU
• 3. Operating rooms
• 4. Surgical
• 5. Cancer chemotherapy wards
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17. Clinical diseases
1. Cutaneous infections
(folliculitis, e.g stye and acne;
furuncles; carbuncles, impetigo).
2.Wound infections: may occur
after surgery or trauma, and
involve skin, bone (osteomyelitis
from an open fracture) or
meninges (meningitis from skull
fracture)
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18. Clinical diseases…
Bacteremia
•Mostly results from surgery or continued use of
intravascular catheters
•Haematogeneous spread of bacteria may result into
• Endocarditis
• Osteomyelitis
• Septic arthritis
• Meningitis
• Pulmonary infection (pneumonia and empyema.)
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19. Clinical diseases…
Aspiration pneumonia in
very young, very old, cystic
fibrosis patients, influenza,
etc.
Staphylococcal scalded skin
syndrome (SSSS or Ritter's
disease)
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20. Clinical diseases…
Bullous impetigo, a
localized form of
SSSS, with the
blisters containing
the bacteria.
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21. Clinical diseases…
Food poisoning: due to ingestion of preformed
enterotoxin in food (meat and carbohydrates), with
short incubation (1-8 hr). Violent nausea, vomiting
and watery diarrhea; no fever; rapid convalescence
Staphylococcal enterocolitis occurs in patients who
have received broad spectrum antibiotics (antibiotic-
associated diarrhea)
Toxic shock syndrome: abrupt onset of high fever,
vomiting, diarrhea, myalgia, scarlatini form rash,
desquamation of palms and soles, and hypotension
with cardiac and renal failure.
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22. Antibiotics/Control
• 1st line drugs: CN, COT, CXM,E, P, MT/OX
• 2nd line drugs: C, CIP, RA, TEI, VA .
• Cleansing of the wound and application of an
effective disinfectant
• Prevention of wide dissemination from
staphylococci carriers is very important . RA plus a
second antibiotics, or some topical agents, may
suppress or cure of nasal carriage.
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