Staphylococcus aureus: Pathogenesis, Clinical Syndromes
PATHOGENESIS:
- Adhere to damaged skin, mucosa or tissue surfaces
- At these sites, they evade defence mechanisms of the host
- Colonize and cause tissue damage
- S.aureus produces disease by
- Multiplying in tissues
- Liberating toxins
- Stimulating inflammation
CLINICAL SYNDROMES:
- Conjuctivitis
CUTANEOUS INFECTIONS:
Folliculitis:
- Inflammation of the hair follicles.
- A small red bump or pimple develops at infection sites of hair follicle.
Sty:
- Folliculitis affecting one or more hair follicles on the edge of the upper or lower eyelid.
Furuncle/boils:
- Deep seated infection, originating from folliculitis,( if infection extends from follicle to neighbour tissue)
- Causes redness, swelling, severe pain
- Commonly found on the neck, armpit and groin regions
Carbuncle:
- Carbuncle is an aggregation of infected furuncles. Carbuncles may form large abscesses.
- It is a large area of redness, swelling and pain, punctuated by several sites of drainage pus.
Bullous Impetigo:
- Very superficial skin infection common in children, usually produces blisters or sores on the face, neck, hands, and diaper area.
- It is characterized by watery bristles, which become pustules and then honey coloured crust
Botryomycosis:
- Cutaneous infection
- Classically occurs on the extremities in areas of trauma
- In immunocompromised individuals.
- Wound infection
DEEP INFECTIONS:
Osteomyelitis:
- Both acute & chronic osteomyelitis is caused by S.aureus
- Bacteria can get to the bone Via bloodstream following an injury
- Clinical features: pain, swelling, deformity, defective healing, in some case pus flow,
- Diagnosis: X-ray, MRI, bone aspirates
Periostitis:
- Clinical features: fever, localised pain, leucocytosis
- Diagnosis: needle aspiration of subperiosteal fluid
Endocarditis:
- It is an inflammation of the inner layer of the heart, the endocardium
- Prosthtetic valve, tooth extraction may be the aggrevating factor in Infective endocarditis by s. aureus
- Endocarditis occurs when bacteria enter bloodstream, travel to heart, and lodge on abnormal heart valves(Prosthetic valve endocarditis ) or damaged heart tissue.
- Myocardial abscess is most common in acute endocarditis caused by Staphylococcus aureus
- Septic arthritis( in children)
- Pneumonia( In patient with bronchiectasis)
Staphylococcal pneumonia
- URTI , pyoderma or other associated purluent disease
- Besides the usual features of pneumonia child has fever and anorexia and is listless and irritable.
- Abdomen is usually distended due to septicemia and ileus.
- Cyanosis may be present
- Most common pathogen causing, pulmonary infection in cystic fibrosis in infants & young children is Staphylococcus aureus
- Sore throat
- Pneumatocoele
- Chest radiograph shows patchy areas of consolidation and multiple bilateral thin walled air containing cysts
Exfoliative diseases:
- ‘Staphylococcal skin scalded syndrome’previously called dermatitis exfoliativa
- pemphigus neonatorum
- Lyell’s disease
- Ritter’s disease
- Epidermal toxin produced by S.aureus at skin and is carried by bloodstream to epidermis
- Split cellular layer i.e., this toxin separates outer layer of epidermis from underlying tissue
TOXIC SHOCK SYNDROME:
- Caused when Toxin shock syndrome toxin (TSST) liberated by S.aureus enters bloodstream
It is a multisystem illness, that occurs due to superantigen& is characterized by:
- High Fever
-
Headache
-
Conjunctival reddening
-
Hypotension
-
Vomiting
-
Diarrhoea
-
Skin rashes
-
Kidney failure
STAPHYLOCOCCUS FOOD POISIONIG:
- Caused when consuming food in which S.aureus has multiplied and pre-formed endotoxin
- Intradietic toxin is responsible for intestinal symptoms.
- Commonly occurs with dairy products
- Optimum temperature for toxin production is 37°C
- Incubation period is 1-6 hours
- Gastroenteritis within 4-6 hrs of consumption of cooked food indicates the cook to be in the carrier state of staphylococcus
- Staphylococcus appear in stool
Symptoms:
- Nausea
- Vomiting
- Severe abdominal cramp
- Diarrhoea
- Sweating
- Headache,etc.
Exam Question
CLINICAL SYNDROMES:
- Conjuctivitis
CUTANEOUS INFECTIONS:
Bullous Impetigo:
- It is characterized by watery bristles, which become pustules and then honey coloured crust
- Botryomycosis
DEEP INFECTIONS:
- Osteomyelitis
- Both acute & chronic osteomyelitis is caused by S.aureus
- Periostitis
Endocarditis:
- It is an inflammation of the inner layer of the heart, the endocardium
- Prosthtetic valve, tooth extraction may be the aggrevating factor in Infective endocarditis by s. aureus
- Endocarditis occurs when bacteria enter bloodstream, travel to heart, and lodge on abnormal heart valves(Prosthetic valve endocarditis ) or damaged heart tissue.
- Myocardial abscess is most common in acute endocarditis caused by Staphylococcus aureus
- Septic arthritis( in children)
- Pneumonia( In patient with bronchiectasis)
Staphylococcal pneumonia
- URTI , pyoderma or other associated purluent disease
- Most common pathogen causing, pulmonary infection in cystic fibrosis in infants & young children is Staphylococcus aureus
- Sore throat
- Pneumatocoele
- Chest radiograph shows patchy areas of consolidation and multiple bilateral thin walled air containing cysts
Exfoliative diseases:
- ‘Staphylococcal skin scalded syndrome’previously called dermatitis exfoliativa pemphigus neonatorum
- Lyell’s disease
- Ritter’s disease
TOXIC SHOCK SYNDROME:
- Caused when Toxin shock syndrome toxin (TSST) liberated by S.aureus enters bloodstream
- It is a multisystem illness, that occurs due to superantigen
STAPHYLOCOCCUS FOOD POISIONIG:
- Caused when consuming food in which S.aureus has multiplied and pre-formed endotoxin
- Intradietic toxin is responsible for intestinal symptoms.
- Commonly occurs with dairy products
- Optimum temperature for toxin production is 37°C
- Incubation period is 1-6 hours
- Gastroenteritis within 4-6 hrs of consumption of cooked food indicates the cook to be in the carrier state of staphylococcus
- Staphylococcus appear in stool
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