Lecture 7 Staphylococcus Flashcards
What is the major location for S. aureus
In the nasal cavity
What are the 3 major Staph that are pathogens and cause most of the disease?
S. aureus
S. epidermidis
S. saprophyticus
Major location for S. epidermidis?
Dry skin or epithelium
Major location for S. saprophyticus
Mucosa, Moist epithelium
Which of the three Staph organisms are Coagulase +?
S. aureus
4 main characteristics of S. aureus
- Coagulase +
- Protein A, many secreted enzymes and toxins
- Frequently Drug Resistant (MRSA)
- Involved in many illnesses such as Food poisoning, Toxic Shock etc.
4 characteristics of S. epidermidis
- No Coagulase
- Capsule
- Frequently drug resistant
- Catheter and prosthetic implant infections
2 characteristics of S. saprophyticus
- No Coagulase
2. Urinary tract infections in young women
What is the #2 cause of UTI’s in women?
S. saprophyticus
Does S. aureus have a high carrier rate?
Yes, it is found in 20-30% of general population at any one time. Carrier rate is higher in Hospital Personnel
Some isolates of S. aureus have become resistant to almost all antibiotics except what?
Vancomycin
Name the 6 virulence factors on S. aureus
- Fibrin binding proteins on cell wall that help colonize cells and tissues
- Protein A
- Many enzymes secreted
- Cytolytic toxins
- Superantigen exotoxins
- Catalase +
How is catalase a virulence factor for S. aureus
Catalase is able to convert the H2O2 secreted by PMN’s and allow S. aureus to survive
What type of toxin is associated with Scalded Skin Syndrome in children
Exfoliative Toxin
How do catalytic toxins work?
They lyse most cells, including host defense cells
Superantigens (virulence factor) stimulate cytokine production which produces what two illnesses?
- ‘True’ Food poisoning
2. Toxic Shock syndrome
What is the name of the Superantigen that produces Toxic Shock Syndrome?
Toxic Shock Syndrome toxin (TSST-1)
How does Protein A work?
It binds to the IgG Fc site, this blocks the phagocyte adherence to IgG opsonization
How does Coagulase work as a virulence factor
produces local fibrin deposition that can act to wall off the infection
Difference between secreted coagulase and surface coagulase
- Surface coagulase coats the staph cells with host fibrin, hiding bacterial epitopes and camoflaging itself from immune system
- Secreted coagulase produces local fibrin deposition that acts as a wall around the bacteria and restrict immune system from entering. This often leads to an abcess
What leads to an abcess?
When Fibrin is deposited by a bacteria and acts to wall off the bacteria from the body and immune system.
Name 3 specific spreading factors
Staphylokinase
Lipase
Hyaluronidase
4 types of local infection caused by S. aureus
Local Skin infections
Deep, localized infections
Acute Endocarditis
Pneumonia
Local skin infections may lead to what?
Cellulitis and Bacteremia
2 examples of Local skin infection
Abscesses (boils, carbuncles)
Impetigo
3 examples of Deep, localized infections
Abscesses of the spleen, liver and kidney
Osteomyelitis
Septic Arthritis
Explain Scalded skin syndrome
An exfoliative toxin (protease) degrades desmosomes releasing the outer layer of epidermis. Rarely fatal and occurs in small babies
Explain ‘True’ Food poisoning
Enterotoxins (superantigen) acting directly or indirectly on the GI tract to induce diarrhea and vomiting. Toxin does the poisoning not the bacteria
What occurs during the Toxic Shock syndrome
Superantigen TSST-1 can be released from a focal infection, most commonly next to a mucosal surface. This toxin activates huge numbers of Th cells and macrophages that release cytokines. This massive release of cytokines causes hypovelemic shock, fever, a skin rash with defoliation, diarrhea and vomiting.
What two bacteria are a common and increasingly dangerous cause of nosocomial and iatrogenic infections
S. Aureus, S. Epidermidis
What is a main way in which antibiotic resistant Staph is proliferated?
They are usually encoded by plasmids that are readily shared between species and strains, even between enteric bacteria and Staph.
Difference between nosocomial infection and iatrogenic infection
Nosocomial: Hospital acquired
Iatrogenic: Doctor acquired
