Transcript Staphylococcus aureus

Gram –Positive cocci
Staphylococcus
Introduction:
)Staphylococcus aureus (yellow
Genus: Staphylococcus
Family: Micrococcaceae (see table 1)
Species: Staphylococcus aureus (most medically important species). It can
causes serious bacterial infections, intoxication, food poisoning, toxic shook
syndrome
Others:
Staphylococcus epidermidis
Staphylococcus saprophyticus
Staphylococcus haemolyticus
Definition :staphylococcus aureus are Gram positive and occur
characteristically in irregular grape-like clusters .
Normal habitat:*
S. aureus is carried in the nose of 40% or more of healthy people.
Epidemiology
Carriers serve as a source of infection to themselves and others e.g. :
Direct contact
By contamination of vomits
Or food which results to food poisoning
Nosocomial infection
Phathogenicity:
1. Common cause of primary localized skin infections including
2. Deep, localized infections these maybe metastatic from superficial infections
or skin, or trauma
ostomyelitis (bown marrow infection)
Arthritis (infection of the joints)
3. Acute endocarditis associated with intravenous drug abuse
4. Septicemia: generalized infection with sepsis or bacteremia
5. Pneumonia and empyema
6. Nosocomial infection its one of the most common cause of hospital acquired
infections
7. osteomyelitis
8. artharitis
9. Toxinoses
A. toxic shock syndrome : TSS :
B. staphylococcus gastroenteritis: is caused by ingestion of food
contaminated with enter toxin, usually contaminated by a food handler these
food tend to be protein rich for example egg salad, cream pastry, ice cream,
and improperly refrigerated, symptom are nausea vomiting and diarrhea after
short period of incubation like 6 hours
C. scalded skin syndrome (Lyell’s syndrome),
Virulence factors
Enzymes and toxins produced by S. aureus
1. Cell wall virulence factor
Protein A
Fibronectin-binding protein FNBP
2. Cytolytic exotoxins ∞, ß, γ,
3. superantigen exotoxins:
4. enterotocxins : six major antigen types A, B, C, D, E, and G)
5. Coagulase
•Deoxyribonuclease (DNAse), that destroys DNA
•Hyaluronidase, that helps S. aureus to spread in the tissues
•Lipase, that breaks down fat
•Staphylokinase, that causes fibrinolysis
•Exofoliatin, that causes peeling of the skin
•Enterotoxin B, that causes food poisoning
•Beta-lactamase (antibiotic-inactivating enzymes), that lead to Penicillin
resistance.
•Capsular Polysaccharide
•Leukocidin
FIGURE 2. Virulence determinants of Staphylococcus aureus
laboratory diagnosis :
Specimens :
Pus
Sputum
Blood
Faeces
If food poisoning suspected (vomiting)
Anterior nasal swap required to detect S. aureus carrier
Swaps from different site infected.
Portion of intravenous device
Direct Microscopy
Culture:
Temperature: optimal (33-37ºC) temperature range (10-42ºC)
Atomospher: aerobically also in carbon-dioxide, most trains grow anerobically.
Time: over night 24 hrs.
Different media
Nutrient agar
Blood agar (Golden yellow- with B-haemolysis when grown areobically) for and
other than S. aureus are white colonies, all easy to emulsify.
MacConckey: small colonies which are pink in color due to lactose
fermentation. Most strains are non-lactose fermented.
Manitol salt agar :
Biochemical reaction
Coagulase test
This test is used to differentiate S. aureus form S. epidermidis and S.
saprophyticus.
Free Coagulase
Bound Coagulase
II. DNAse
If plasma is not available or the Coagulase test are not clear.
This test is used to differentiate S. aureus which produces the enzyme DNAse from
other staphylococci which don’t produce DNAse.
Catalase test:
To differentiate staphylococcus species are catalase positive where from
streptococcus species are catalase negative.
Antimicrobial sensitivity
Penicillin resistance most of staph are resistance to penicillin G . This has required
the replacement of the initial agent of choice, penicillin G by B-lactamase –
resistance penicillin such as nafcillin or oxacillin
Methecillin resistant test:
Medium is trypticase soya agar salt (TSA)
MRSA: methecillin resistant S. aureus
MSSA. Methecillin sensitive S. aureus
vancomycin : the drug of choice for MRSA, but the possibility that this
resistance my increase in strength spread to other species
prevention
there is no effective vaccines against S. aureus so infection control procedures
such as barier precautions, washing hands and vomits are important in
control of nosocomial infection,