Staphylococcus aureus Flashcards
Motility:
non-motile
Catalase:
positive
Gram reaction:
gram positive cocci in clusters
Atmosphere requirements:
Environmental air. Facultative anaerobe
Areas of the body where SA is a commensal:
Skin and mucosal membranes
Which percent of the population is colonized by SA in their nares?
20-40%
What are the virulence factors of SA?
Capsular polysaccharides and biofilm formation
Adhesins
Unique peptidoglycan cell wall with teichoic and lipoteichoic acids
Protein A
Enzymes
Hemolysin
Leukocidins
Toxin production
Superantigens
Colony morphology:
Large, smooth colonies. Some strains are pigmented (golden). Some strains are beta-hemolytic.
What does the polysaccharide capsule of SA do?
Promotes adherence to host cells and prosthetic devices. Prevents ingestion by PMNs. Alters the binding of complement.
70-80% of significant isolates belong to one of these two serotypes:
Serotype 5 or 8
What is the chemical makeup of peptidoglycan?
Cross-linked polymers of N-acetylglucosamine and N-acetylmuramic acid
What do the teichoic and lipoteichoic acids in the peptidoglycan wall do?
Help adhere to mucosal surfaces and anchor into cell wall enzymes
Which gene codes Protein A?
spa
What does Protein A do?
Binds to Fc region of all IgG (except IgG3), von Willebrand Factor, and complement protein C3. In doing so, it interrupts the signaling that occurs to initiate an immune response.
What is clumping factor?
Enzyme responsible for binding SA to fibrin and fibrinogen.
What is coagulase?
Free or cell bound enzyme. Binds and activates prothrombin, promoting the conversion of fibrinogen to fibrin.
What are fibrinolysins?
Enzymes that breaks down fibrin clots, allowing SA to infect nearby tissues.
What is hyaluronidase?
Enzyme that breaks down mucopolysaccharides, allowing SA to invade other tissues.
What do the lipases SA has do?
Aid in the spread to cutaneous and subcutaneous areas
What is alpha-hemolysin?
Toxin produced by SA that is responsible for the beta hemolysis around cell growth on SBA. This can cause monocytes, macrophages, lymphocytes, and erythrocytes to lyse.
What is beta-hemolysin?
Toxin produced by SA that hydrolyzes sphingomyelin. Cytotoxic to monocytes and erythrocyte susceptibility varies between animal species. Responsible for synergistic hemolysis observed in positive CAMP test.
What are exfoliatins?
Epidermolytic toxins responsible for the clinical presentation of “SSSS.” There are two proteins usually associated with SA. ET-A is carried on a chromosome while ET-B is carried on a plasmid.
How long does Staphylococcal food poisoning last?
2-8 hours
Which enterotoxins are responsible for Staphylococcal food poisoning?
A-E, H, and I
What are the classic signs of toxic shock syndrome?
Fever >102 degrees F, diffuse macular erythroderma, desquamation of palms and feet 1-2 weeks after onset of illness, hypotension <90mmHg, plus the involvement of three or more organ systems
How does Staphylococcal bacteremia present?
Chills, rigor, fever, small hemorrhagic skin lesions, necrotic ulcers
How does Staphylococcal endocarditis present?
Janeway lesions, Roth spot, splinter hemorrhages, heart murmur, pericardial effusion.W
What are common Staphylococcal skin infections?
Folliculitis, impetigo, furuncles, carbuncles, hidradenitis supperativa, mastitis, wound infection, and cellulitis.
When does Staphylococcal meningitis occur?
Primary: local trauma involving neuro surgery. Secondary due to complicated bacteremia.
How does Staphylococcal pneumonia present?
Tissue necrosis with cavitation, bacteremia, lung abscesses, pleural empyemas.
How does Staphylococcal osteomyelitis occur?
Complication of local infection with hematogenous seeding
