12. Staphylococci Flashcards by Giorgia Tanner

What are the lab results for all staphylococci?

Gram positive cocci in clusters

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Where does staph aureus colonise?

Moist skin folds
Mucosa
Nasopharynx

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What is the portal of entry of staph aureus into the body?

Ingestion

Break in skin

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What factors allow staph aureus to attach to cells?

Surface proteins
Capsule
Fibrin/fibrinogen binding protein
Matrix binding proteins

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What is the function of coagulase?

Produces clots to protect from phagocytosis

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What is the function of protein A, which is found on the cell wall of staph aureus?

Prevents phagocytosis

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What is the function of alpha toxin?

Lysis of monocytes and platelets

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What does leukocidin/PVL cause?

Skin and soft tissue infections

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What is the function of staphylokinase?

Dissolves clots to allow spread

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What is the function of hyaluronidase?

Breaks down hyaluronic acid in connective tissue which allows further spread

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What 3 methods can staph aureus use to cause damage to the host?

Direct
Enzymes
Toxins

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How does staph aureus cause direct damage to the host?

Peptidoglycan wall increases cytokine release

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What 2 types of toxins are released by staph aureus?

Superantigens Eg. toxic shock syndrome toxin, enterotoxin

Exfoliative toxins Eg. epidermolytic toxin

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How does staph aureus spread?

Person to person or via environment

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What is the difference between a furuncle and a carbuncle?

Furuncle is a single collection of pus with a single point of drainage
A carbuncle is a collection of boils which have multiple points of drainage

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Name the skin and soft tissue infections caused by staph aureus?

Folliculitis
Mastitis
Styes
Boils
Impetigo
Cellulitis
Necrotising fasciitis
Scalded skin syndrome
Toxic shock syndrome

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What systemic infections are caused by staph aureus?

BSI
Endocarditis
Pneumonia
Osteomyelitis
Septic arthritis

What are the risk factors for endocarditis?

IV catheter
SSI
Surgical valve replacement

What are the risk factors for pneumonia?

Influenza
CF
on ventilator

How is osteomyelitis diagnosed?

Bone biopsy
Direct needle aspiration
MRI

What investigations take place when toxic shock syndrome is suspected?

History
FBC
U&amp;E
Lactate
Wound swab

How is toxic shock syndrome managed?

Rapid IV antibiotics
Resus
Care for wounds

What toxin mediated infections are due to staph aureus?

Food poisoning
Scalded skin syndrome
Toxic shock syndrome

What is Nikolsky’s sign?

Peeling of layers of skin in scalded skin syndrome

What groups of people is scalded skin syndrome most common in?

Neonates Immune compromised Renal failure

What are the symptoms of toxic shock syndrome?

Fever Low BP Rash

What are the possible complications of toxic shock syndrome?

Renal failure | CNS and muscular involvement

What is the method of resistance present in MRSA?

Altered penicillin binding protein | Causes resistance to most beta-lactam antibiotics

What gene causes MRSA?

mecA

Which antibiotics can still be used for an MRSA infection?

Vancomycin Linezolid Daptomycin

What infections are caused by community acquired MRSA?

Skin infections | Pneumonia

What toxin is present in MRSA?

PVL

How are staph aureus infections managed?

``` History and clinical exam Blood tests Microbiology specimen depends on site of infection Radiology Antibiotics if needed ```

What blood tests are useful in a staph aureus investigation?

FBC CRP U&E lactate

What is the preferred antibiotic for MSSA?

Flucloxacillin

Which antibiotics are used for MRSA?

Vancomycin | Teicoplanin

What sorts of infections are caused by staph epidermidis?

Infections associated with prosthetic devices as it forms a biofilm

What infection is caused by staph saprophyticus?

UTI (cystitis)

Which staphylocci are coagulase positive and which are negative?

Aureus is positive | Epidermidis and saprophyticus are negative

How does mannitol salt agar differentiate between sub species of staph?

Aureus ferments and turns yellow | Epidermidis remains pink

How is mannitol salt agar selective?

Staph can withstand high levels of salt, as it colonises on skin High salt levels can stop other bacteria growing

What susceptibility test is used to differentiate between staph saprophyticus and epidermidis?

Novobiocin | Saprophyticus is resistant