Staphylococci Flashcards
What is the gram stain for staphylococci?
Gram positive - PURPLE
What shape are staphylococci?
Cocci in clusters
What are the common types of staphylococci?
Staph aureus, epidermis and saprophyticus
Which type of staphylococcus is the most virulent?
Staph aureus
How does Staph aureus enter the body?
Via a break in the skin
Is staph aureus naturally found in the body?
Yes - on skin and mucous membranes
Name some virulence factors for Staph aureus
Polysaccharide capsule
Protein A
Fibronectin
Cytolytic exotoxin
How is the polysaccharide capsule a virulence factor?
Increases resistance to phagocytosis
How is protein A a virulence factor?
Protein A in the cell wall binds to Fc region of IgG, exerting its anti-opsonin effect therefore strong anti-phagocyte
How do suprantigen exotoxins work as virulence factors?
They have the ability to bind to MHC class II hence stimulate enhanced T cell response. This can cause toxic shock syndrome because of the huge amounts of T cell production.
How is staph aureus transmitted?
Common transmission is via a break in the skin. Also can enter via the respiratory tract
How can you identify staph aureus in a lab?
Stains strongly gram positive
Appears in grape-like clusters
Yellow and haemolytic
Coagulase positive
What is a serious complication of staph aureus?
Sepsis
What can staph aureus cause?
Skin infection - cellulitis and impetigo Septic joint Pneumonia Toxic shock MRSA
What is the treatment for staph aureus?
Resistant to a number of B-lactam antibiotics
What does MRSA stand for?
Methicillin resistance staphylococcus aureus
How is MRSA spread?
Via skin contact and contact with clothes, sheets etc
Why is MRSA so resistant?
Gene for distinct penicillin bound protein (PBP-2a). This protein codes for a new peptidoglycan transpeptidase with a low affinity for B-lactate antibiotics.
How do we treat MRSA?
Vancomycin given intravenously - this is a glycopeptide antibiotic
Describe some features of staphylococcus epidermis?
Coagulase negative staph
What can staph epidermis result in?
Infection of implants such as prosthetic heart valves and catheters
Describe virulence of staph epidermis.
Low virulence however, produces slime that facilitates adherence to bioprosthetic material surfaces. Also slime acts as a barrier to antimicrobials
Describe some features of staph saprophyticus?
Coagulase negative staph
Where is staph saprophyticus found?
Normal vaginal flora
