Lab 28: Bacteria of the skin Flashcards
what organ is the skin?
the largest organ of the body
what are the skin’s functions?
Physical barrier to pathogens
Senses environment
Regulates temperature
Restricts loss of fluids
what line of defense is the skin?
first line of defense
what are the 3 layers of the skin?
- Epidermis (most surface level)
- Dermis
- Hypdermis (deepest layer)
describe the epidermis
-Outermost, avascular layer (no blood vessels).
-Made of 4-5 layers
-Stratum basale: deepest layer
-Stratum corneum: topmost layer
what does the stratum basale contain?
Bottom most/deepest layer:
-1 cell thick
-Made of basal cells, which are alive
-Cells undergo division, new cells pushed out towards the top layers
what does the stratum corneum contain?
Topmost/surface layer:
-10-35 cells thick
-Made of dead cells called keratinocytes
-Constantly flake off carrying away pathogens (flushing action)
-Basal cells differentiate into keratinocytes as they move up, they make keratin, waterproofing lipids, change shape from cuboidal to flat, lose organelles and die
what does the dermis layer contain?
-connective tissue layer
-contains nerves, glands, blood vessels, lymphatic vessels, adipocytes, and hair follicles
-has pressure, temperature, and pain receptors
-provides nourishment to the epidermis
what are three ways that the dermis helps to fight off pathogens?
- Sweat glands: produce salty sweat that inhibits microbes
- Sebaceous glands: produce sebum, an oily secretion that keeps hair and skin soft, flexible, and water-repellant.
- Normal microbiota: break down (aka metabolize) lipids into toxic fatty acids that inhibit microbes and are toxic to pathogens.
what is the hypodermis?
-Subcutaneous tissue
-Contains adipose tissue and blood vessels
what are common skin microbiota/common skin bacteria:
- Propionibacterium (G +)
- Staphylococcus (G +)
- Including S. epidermidis and S. aureus - Corynebacteriaceae family (G +)
- Proteobacteria phylum (G -)
what is Staphylococcus epidermis part of?
The normal microbiota
what type of clusters are found in Staphylococcus epidermis?
Gram positive cocci in clusters
can S. epidermidis cause infection? is it virulent?
It can cause infection if they enter a wound or are displaced - it is NOT very virulent.
However, it can cause severe infections only in immunocompromised.
what is Staphylococcus aureus a part of?
Transient microbiota of the skin, and nasal passage
what type of clusters are S. aureus found in?
Gram positive cocci in clusters
how many people are asymptomatic carriers of S. aureus?
2-30% of people are asymptomatic carriers. You can be a carrier and still pass it on to other people
can S. aureus cause severe infections?
Yes, it can cause severe infections like pneumonia, staphylococcal scalded skin syndrome, staphylococcal food intoxication, staphylococcal TSS, etc.
how can we identify S. aureus in the lab?
Using the MSA medium: high salt (7.5%) NaCl allows the growth of halotolerant skin bacteria.
how does S. aureus show up on the MSA plate?
S. aureus ferments mannitol and turns yellow on MSA plates; S. epidermidis stays pink.
If we see yellow colonies, we know we are a carrier of S. aureus.
We have to confirm that S. aureus is actually present since we cannot only rely on the MSA test. What other tests can we use to determine if S. aureus is present?
It is:
Gram +
Catalase + (H2O2)
Coagulase +
what happens when you have a coagulase + test?
-During normal clotting, signals from damaged tissues activate plasma protein prothrombin to form thrombin.
-Thrombin converts plasma protein fibrinogen into fibrin - which is an insoluble protein that forms a mesh that traps blood cells to form a clot.
-Coagulase activates thrombin causing S. aureus to coat itself with fibrin mesh - which helps it to hide/evade the immune system and attached to the cells to cause infection.
what do we incubate for a coagulase test?
bacteria + rabbit plasma incubated at 37 degrees C for 4 hours
how do you know if a coagulase test is + for S. aureus?
Coagulations
if there is no coagulation, what do we conclude?
CoNS (coagulase-negative staphylococci)
how does S. aureus hide from the immune system?
it covers itself with a fibrin mesh/clot formed by coagulase
what kind of infection can S. aureus cause?
Hair follicle infections - S. aureus enters the skin through hair follicles to the dermis and causes inflammation, etc.
what is folliculitis?
First stage of the infection:
Inflammation of hair follicles.
Small red bumps or pimples form, it is self-clearing.
what is Fununcle (boil)?
Second stage of the infection:
Infection spreads to adjacent tissue.
Abscess formation (redness, swelling, pain).
what is the carbuncle?
Third stage of the infection,
Infection spreads to a larger area.
Abscess + fever.
May require minor surgery to drain pus
Antibiotics given
what is the prevention of hair follicle infections?
hand washing
why is S. aureus so good at causing infections?
Because of its virulence factors
what are the 6 virulence factors of S. aureus?
- Capsule
- Clumping factor
- Protein A
- Coagulase
- Enzymes
- Toxins
what does the capsule do for the virulence factor?
prevents phagocytosis (basically prevents binding of sentinel cells)
what does the clumping factor do for the virulence factor?
allows cells to crosslink and form a big clump that is hard to phagocytose; allows attachment of cells to damaged host cells and medical devices coated with fibrinogen
what does Protein A do for S. aureus virulence factors?
prevents opsonization and ADCC
what does coagulase do for S. aureus virulence factors?
S. aureus forms a clot of fibrin mesh around itself to help evade the immune system
what do enzymes do for S. aureus virulence factors?
break down host proteins, lipids, etc.
what do toxins do for S. aureus virulence factors?
kills host cells including leukocytes (WBCs)
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