Staphylococcus Aureus 1. Main biological features a. Cell shape, arrangement, Gr
ID: 147349 • Letter: S
Question
Staphylococcus Aureus
1. Main biological features
a. Cell shape, arrangement, Gram stain, endospores, capsule, unusual features.
2. Clinical Manifestations
a. List the diseases that are produced by this microorganism.
3. Mechanism of Disease
a. List of how the microorganism induces disease: Toxin, proteolysis, pyogenic, immunological mechanism or multiple mechanisms.
4. Transmission
a. How the microorganism is transmitted and who is at risk of acquiring the infection.
5. Prevention
a. List the most common prevention methods
b. Is there a vaccine?
6. Treatment
a. Is antimicrobial intervention necessary?
b. Have resistant strains been detected?
c. List the common methods of treatment (you don’t need to list drug names).
d. Prognosis – Mortality associated with the disease
Explanation / Answer
Staphylococcus Aureus
1. Main biological features
a. Cell shape: spherical cocci
arrangement: grape like cluster
Gram stain: gram positive
endospores : absent
capsule: in young cultures
unusual features: produce golden yellow pigment on Nutrient agar media
2. Clinical Manifestations:
Pyigenic infections
Fever
Localised pyogenic lesions
a.diseases that are produced by this microorganism:
Foliculitits
Furuncle
Carbuncle
Tonsillitis
Pharyngitis
Sinusitis
Otitis
Meningitis
Endocarditis
Arthritis
Brinchopneumonia
Food poisoning
3. Mechanism of Disease
Toxins: hemolysins
Leucocidin
Toxic shock syndrome toxin
Enterotoxin for food poisoning
Staphylococcus aureus are pyogenic bacteria that cause localized lesions in contrast to streptococci that are spreading in nature. Staphylococci adhere to the damaged skin, mucosa, or tissue surfaces. At these sites, they evade defense mechanisms of the host, colonize, and cause tissue damage. They produce disease by: Liberating toxins,
multiply in the host
and
Stimulating inflammation.
4. Transmission:
Human cases and carriers are the important reservoir of infection.
Human cases of cutaneous and respiratory infections shed large numbers of staphylococci into the environment for a prolonged period of time. Staphylococci colonize the skin very early in life (in neonates on the umbilical stump).
Staphylococci shed by the patients and carriers contaminate handkerchiefs, bed linens, blankets, and other inanimate fomites and persist in them for weeks.
S. aureus found in the nose and sometimes on the skin, especially in hospital staff and patients is the main source of infection in hospitals.
Domestic animals, such as cows, can also be reservoirs of staphylococcal infection.
5. Prevention:
There is no effective immunization with toxoids or bacterial vaccines against staphylococcal infection. Cleanliness, frequent hand-washing, and aseptic management of lesions help in the control of S. aureus infection
6. Treatment:
Skin and soft tissue infections are treated best with local wound care with or without topical antibiotics (e.g., neomycin). Spontaneous or surgical drainage of pus and debridement of necrotic tissue is an effective mode for treatment of staphylococcal abscess. Systemic antibiotics are necessary for deep-seated and systemic infections.
Penicillin resistance in staphylococci and Methicillin-resistant staphylococci species have emerged.
Methicillin-resistant S. aureus (MRSA) denotes resistance of S. aureus to penicillin, as well as to all other beta-lactam antibiotics including the third-generation cephalosporins and carbapenems.
MRSA strains can be treated with glycopeptide antibiotics, such as vancomycin and teicoplanin in serious systemic infections, such as pneumonia, bacteremia, and endocarditis. MRSA are sensitive to one or more of the second-line drugs, which include erythromycin, clindamycin, quinolones, fusidic acid, trimethoprim, chloramphenicol, tetracycline, and rifampicin
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