Lecture 9: Staphylococcal Flashcards
What are the 2 divisions of Staphylococcus?
Coagulase + are usually S. aureus and pathogenic
Coagulase - are organisms like S. epidermidis are less invasive
What are the General Characteristics of the Staphylococci?
- common inhabitant of the skin and mucous membranes
- Spherical cells arranged in irregular clusters
- Gram-positive
- Lack of spores and flagella
- extracellular pathogen
What are the characteristics of staphylococcus aureus?
- Grows in large round colonies-grape like
- Golden yellow colonies on blood agar plate
- Facultative anaerobe
- Withstands high salt, extremes in pH, and high temperatures
What are the 2 divisions of disease produced by staphylococcus aureus?
- Infections
2. Intoxication
What are the stages of the mechanism of pathogenesis of staphylococcal infection?
- bacteria gains access to damage skin, mucosa or tissue site
- colonized by adhering to cells or extracellular matrix
- evade the host defense mechanism and multiple
- causes damage
What are the bacteria portals in the local infection affecting skin and soft tissue of staphylococcal disease?
- hair follicle
- break in the skin (needle-stick or a surgical wound)
What are the 4 types of system infection of staphylococcus?
- osteomyelitis
- bacteremia
- endocarditis
- pneumonia and empyema
What is osteomyelitis?
S. aureus invasion of the bone (through wound or bacteremia), inflammation of bone marrow and surrounding bone
What is bacteremia?
bacteria in the blood. Primary origin is bacteria from another infected site or medical devices
What is endocarditis?
attacks the lining of the heart (including its valves). Non-specific flu-like symptoms but conditions quickly worsens as the amount of blood pumped from the heart drops.
50% mortality rate.
What is the difference between pneumonia and empyema?
Pneumonia - inflammation of lungs, fluid fills within alveoli and bronchioles.
Empyema - collection of pus in the space between the lung and the inner surface of the chest wall.
What are the 3 types of intoxication of staphylococcus?
- food
- skin - staphylococcal scaled skin
- toxic shock syndrome
What is food intoxication?
ingestion of heat-stable enterotoxins (not the bacteria itself); gastrointestinal distress
What is scalded skin syndrome?
toxin induces bright red flush, blisters, then pealing of the epidermis
What is toxic shock syndrome?
toxemia leading to shock and organ failure
What are the symptoms of toxic shock syndrome (TSS)?
8-12 h post infection Fever Susceptibility to Endotoxins Hypotension Diarrhea Multiple Organ System Failure Erythroderma (rash)
What is the structural component of protein A?
Type I membrane protein which binds immunoglobulin (IgG) molecules on their heavy chain within the Fc region to render them ineffective
What are some traits of Coagulase?
Can be bound to the outer surface of the bacteria or cell-free
Highly correlated with virulence - most (but not all) virulent strains are coagulase positive
What are the extracellular factors of s. aureus?
- Enzymes
2. toxins
What does Hyaluronidase do?
- Breaks down hyaluronic acid, major component of the matrix between cells (digests connective tissue)
- Enables bacteria to spread between cells throughout the body
What does Staphylokinase do?
Dissolves fibrin threads in blood clots, allowing S. aureus to free itself from clots
Helps bacterial spread to new locations
What are the functions of lipases S. aures?
They hydrolyze lipids
they may help the bacteria survive in sebaceous glands in the skin (enhances colonization)
may aid in development of skin infections and subcutaneous infections
What do hemolysis do?
Hemolysins (α, β, γ, δ) – lyse red blood cells
What is delta toxin?
a very small peptide toxin produced by most strains of S. aureus and S. epidermidis that lyse red blood cells
What do B-toxin do?
sphingomyelinase which damages membranes rich in this lipid
The majority of human isolates of S. aureus do not express ß-toxin
What do Leukocidin do?
lyse neutrophils and macrophages
What are the causes of community-acquired MRSA?
skin/soft tissue infections (77%) wound infections (10%) urinary tract infections (3%) bacteremia (3%) lung infections (2%) Other infections: necrotizing pneumonia, severe sepsis, necrotizing fasciitis, endocarditis, etc.
Where are the common outbreaks of community-MRSA?
Prisons
Child day-care centers
Sports teams
Military recruits
Why has vaccine efforts been vain for s. aureus?
S. aureus expresses a large array of virulence factors such that a vaccine against any one may not prove effective.
What is infection?
The disease is caused by the bacteria themselves
What is intoxication?
The disease is caused by bacterial exotoxins, which are produced either in the infected host or performed in vitro
what are some of the pre dispositions to infection?
- poor hygiene
- poor nutrition
- tissue injury
- preexisting primary infection
- diabetes
- immunodeficiency
what are traits of cell associated polymers?
- cell wall polysaccharide
- teichoic acid (in peptidoglycan layer of gram positive)
- capsular polysaccharide
how does Staph protect itself from phagocytosis?
- protein A
- bound coagulase
- capsule
What does coagulase capsule do?
- inhibits chemotaxis of and endocytosis by leukocytes and aids in attachment
- Converts fibrinogen into insoluble fibrin which causes clotting
What are the enzymes for virulence of staphylococcus?
- free coagulase
- catalase
- lipase
- hyaluronidase
- DNAase
- thermonuclease
- staphylokinase
- phosphatase
What do DNase do?
marker for virulence, digests DNA
What does penicillinase do?
inactivates penicillin
What do enterotoxins do?
- they stimulate muscle contractions, nausea, and intense vomiting associated with food poisoning.
- when expressed systemically, can cause toxic shock syndrome
How does alpha hemolysin work?
- binds to the membranes of susceptible cells in a monomeric form
- subunits then oligmerize to form heptameric rings with central pore through which cellular contents leak
- Platelets and monocytes are particularly sensitive to alpha toxin
What do exfoliative toxins do?
separates the epidermis from the dermis
What do Toxic shock syndrome toxin (TSST) do?
induces fever, vomiting, shock, systemic organ damage
which toxins have superantigen activity?
- enterotoxins, they stimulate T cells non specifically without normal anitgenic recognition
- toxic shock syndrome toxin
what are the 6 antigenic types of enterotoxin?
SE-A through SE-G
what is special about enterotoxins B and C?
cause 50% of non menstrual cases of TSS
what are the properties skin has to prevent S. aureus colonization?
- low temperature
- low pH
- skin commensals
- antimicrobial peptides
what do keratinocytes do?
they produce keratin and express recognition receptors such as TLR2 and NOD2
what does TLR2 do?
recognizes S.aureus lipopeptides and lipotechoic acid
what does NOD2 do?
recognizes S. aureus peptidoglycan breakdown product muramyl-peptide
what does TLR2 and NOD2 signaling lead to?
activation of NF-kB and other transcription factors that induce transcription of pro-inflammatory mediators
what does S. aureus infection of skin result in?
- production of IL-1a, IL-1b, and IL-17
- induce keratinocyte production of anitmicrobial peptides
- granulopoiesis factors that promote neutrophil recruitment
what is Mecin/PBP2a?
a penicillin binding protein that is intrinsically insensitive to methicillin and all beta lactams that have been developed
What is Protein A?
an abundant surface protein that is able to interact with the Fc portion of immunoglobulin, suppressing the adaptive immune response by limiting B cell antibody production.
What do Coagulases do?
Converts fibrinogen into insoluble fibrin which causes clotting
What doe B-lactamase influence?
treatment options
What species of Staphylococcus produces delta toxins?
S. epidermidis.
