What is a superantigen?
What biological and physiological effects does a superantigen have?
A substance that causes proliferation of entire subsets of T cells (those w/ T cell receptors w/ specific Vß domains)
Large amounts of cytokines such as IL-1 and TNF are released
Cytokines cause fever, shock, and organ failure
What are the steps in pathogenesis?
- Enter the host
- Adhere to the host
- Multiple, persist, damage the host (invade into cells, secrete toxins, evade immune response)
- Spread to next host sometimes
What are Staphylococci?
Gram-positive cocci that grow in grape-like clusters
What are the three medically important staphylococci?
- Staphylococcus aureus
- Staphylococcus epidermidis
- Staphyloccocus saprophyticus
What is important about Staphylococcus saprophyticus?
Staphylococcus saprophyticus is a common cause of UTIs in young women
What is important about Staphylococcus epidermidis?
Staphylococcus epidermidis is adept at attaching to and growing on prosthetic devices
(normal inhabitant of skin, nose, and mouth of humans; less virulent than S. aureus)
Staphylococcus aureus is a [Gram, shape, description, metabolic]
Gram-positive cocci that grows in grape-like structures and is a facultative anaerobe
What is the most virulent of the staphylococci?
Which compounds determine the pathogenicity of Staphylococcus aureus?
- Toxic shock syndrome toxin 1 (TSST-1)
- Staphylococcal enterotoxins A-E, G-I
- Exfoliatin (exfoliative toxin)
- Alpha toxin (alpha-hemolysin)
- Panton-Valentine leukocidin (PVL)
- Protein A
Why is TSST-1 from Staphylococcus aureus relevant?
How does TSST-1 exert systemic effects?
What sort of antigen is TSST-1?
Cause of most cases of bacterial toxic shock syndrome
May be produced by staphylococci growing at an isolated site, reach the bloodstream, and cause systemic effects without bacteremia
Why are Staphylococcal enterotoxins A-E and G-I relevant?
How do they exert their effects?
Why are they hard to kill?
Cause staphylococcal food poisoning and toxic shock syndrome
Act directly on neural receptors in upper GI tract, stimulating vomiting center in brain to cause vomiting 2-5 hrs after ingestion
Resistant to boiling for 30 minutes and digestive enzymes
What condition does exfoliatin from Staphylococcus aureus cause?
How does it do that?
Scalded skin syndrome
Disrupts intercellular junctions in the skin, leading to splitting of epidermis between stratum spinosum and stratum granulosum
What kind of toxin is alpha-toxin from Staphylococcus aureus?
What kind of factor alpha-toxin an example of?
(inserts into lipid bilayers of mammalian cells, forms pores, causes cell death and tissue destruction)
(lyses RBCs when bacteria are grown on blood agar plates, thought to lyse other types of cells during infections or disrupt intercellular junctions in epithelial barriers)
What kind of toxin is Panton-Valentine leukocidin from Staphylococcus aureus?
What sort of Staphylococcus aureus infection is it associated with?
How does it work?
What is the gene for PVL carried by?
Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA)
Contributes to cell lysis, causing severe necrotic infections associated w/ many CA-MRSA strains
What is the function of coagulase from Staphylococcus aureus?
How does it work?
Helps create a mechanical barrier that blocks off neutrophils
- Binds to prothrombin to form a complex
- Complex initiates polymerization of fibrin to form a clot
- Fibrin contributes to fibrin capsule surrounding many abscesses
- Mechnical barrier prevents neutrophils from entering abscesses
What is the function of Protein A from Staphylococcus aureus?
How does it work?
Prevents antibody-mediated immune clearance
Binds to Fc portion of IgG molecules
What clinical diseases does Staphylococcus aureus cause?
- Joint and bone infections
- Toxic shock syndrome
- Staphylococcal food poisoning
- Scalded skin syndrome
- Skin and soft tissue infections
- Hospital-acquired infections (nosocomial)
How does Staphylococcus aureus cause joint and bone infections?
Gains access to bloodstream and causes infections at distant sites such as joints (septic arthritis) and bones (osteomyelitis)
How does Staphylococcus aureus cause endocarditis?
Why does this often lead to death?
Which population is this especially common in?
What are the clinical signs?
Staphylococcus aureus goes to the bloodstream and causes localized infection of valves of the heart
Bacteria form biofilms on heart valves and a very difficult to eradicate with antibiotics
IV drug users
Osler's nodes, Janeway lesions, conjunctivital hemorrhages, heart murmurs
What are the symptoms of toxic shock syndrome from Staphylococcus aureus?
What tends to occur upon resolution of toxic shock syndrome?
What is this illness most associated with?
What is this illness also associated with?
Are blood cultures positive or negative?
High fever, vomiting, diarrhea, sore throat, muscle pain, rash, hypotension or shock that can lead to organ failure
Desquamation of skin, especially digits
Most common cause: tampon use (strains that colonize vagina and produce TSST-1)
Wound infections (S. aureus enterotoxins or TSST-1 are the cause)
Blood cultures are negative
Which toxin is the cause of food poisoning in Staphylococcus aureus?
Describe food poisoning due to Staphylococcus aureus
A self-limited episode of vomiting and diarrhea that begins 2-5 hrs after ingestion of food contaminated w/ enterotoxins
Which toxin is the cause of scalded skin syndrome due to Staphylococcus aureus?
What is the main symptom?
Which age groups are primarily affected?
Describe the localization of the infection
Infants and children under 5 years old
Infection is usually localized, such as conjunctivitis, but exfoliatin reaches bloodstream and may cause exfoliation at remote sites
What is the difference between a furuncle and a carbuncle?
Furuncles are boils, most of which begin with the blockage of hair follicle or sweat gland that subsequently becomes infected
Carbuncles are multiple abscesses formed after infection spreads from a furuncle
What types of skin and soft tissue infections does Staphylococcus aureus cause?
- Furuncle and carbuncle
- Cellulitis (also folliculitis, other soft tissue infections)
Which two types of bacteria tend to cause skin infections?
Staphylococcus aureus, group A streptococci
What is a nosocomial infection?
An infection acquired after people are admitted to the hospital and have undergone procedures
Describe the diagnostic laboratory test findings for Staphylococcus aureus
- Easily culturable on blood agar plates and seen on Gram-stain of tissue specimens
- Colonies have a gold color
- Catalase positive
- Coagulase positive
How can you differentiate Staphylococcus aureus from streptococci using a lab test?
Staphylococcus aureus is catalase positive
Streptococci are catalase negative
How can you differentiate Staphylococcus aureus from Staphylococcus epidermidis and Staphylococcus saprophyticus on a lab test?
Staphylococcus aureus is coagulase positive
Staphylococcus epidermidis and Staphylococcus saprophyticus are coagulase negative
How is Staphylococcus aureus infection treated?
Why is treatment difficult?
Drainage of all collections of pus and antibiotics
Almost all isolates produce a beta-lactamase that degrades penicillin
Antistaphylococcal penicillins (methicillin, nafcillin, oxacillin) and cephalosporins are resistant to beta-lactamases but MRSA is resistant to the antistaphylococcal penicillins
VRSA is resistant to vancomycin