28. Bacteria Of The Skin Flashcards
What are the 3 layers of the skin?
1) epidermis
2) dermis
3) hypodermis
What are the characteristics of the epidermis?
- most superficial layer
- avascular (lacks blood vessels)
- varies in composition in different parts of the body
- 10-35 cells in thickness
What are the 2 layers of the epidermis explained in the lab?
- stratum basale (deepest part of epidermis)
- 1 cell thick
- contain basal cells that are attached to the basement membrane
- stratum Corneum (most superficial)
- 10-35 cells thick
- contain keratinocytes (inactive and lack organelles)
- constantly slough from the skin
As basal cells are pushed away from the stratum basalem they undergo a differentiation process. What happens here?
- synthesis of keratin and secretions of waterproofing lipids
- cell membranes get thicker and organelles are broken down.
- they also change shape going from cuiboidal to squamous
What are the characteristics of the dermis?
- contains blood vessels, fibroblasts, collagen fibers, adipocytes, hair follicles, sweat glands
- contains pressure, temperature, and pain receptors
What are the characteristics of the hypodermics/ subcutaneous layer?
- deepest layer of the skin
- contains mostly adipose tissue (fat)
What are the 4 common groups of skin bacteria?
1) Propionibacterium genus (gram +)
2) Staphylococci (gram +)
3) Corynebacterium (gram +)
4) proteobacteria (gram -)
2 common skin bacteria (characteristics)
Staphylococcus epidermidis
- normal microbiota - Gram + cocci, clustered growth - not highly virulent - severe S. Epi infections limted to immunocompromised persons
Staphylococcus aureus
- Gram + coccus - colonizes the skin - classified as a primary pathogen
All members of the Staaphylococcus genus is able to grow on what kind of media? What kind of medium can be used?
- high salt media
- MSA: contains height concentration of salt (7.5%)
-high salt media suppresses the growth of many organisms, but not S. Epi and S. Aureus
How is S. Epidermidis and S.Aureus differentiated using MSA?
- MSA contains mannitol and a pH indicator
- S. Aureus ferments mannitol to acidic products (lactic acid) > grows yellow colonies
- S. Epidermidis does not ferment mannitol > grows pink or red colonies
S. Aureus cells secrete what kind of protein? What is its function
- coagulase
- activates prothrombin, turning it into thrombin
- Thrombin allows S. Aureus cells growing inside people to coat themselves with fibrin mesh
- contributes to the virulence of S. Aureus (avoids detection, attach, trigger inappropriate blood clots near sites of infection
Why are the cells of the stratum corneum not adequate hosts for viruses?
- cells are dead
- not able to do protein synthesis or nucleic acid replication
Describe the mechanical and physiological antimicrobial defenses found on and in the skin
1) many layers; anchoring proteins
2) skin is thick
3) outer layers (stratum corneum)
- dead cells
- no viral replication
- keratin protein (hard to digest)
4)perspiration >salts > inhibit some microbes
5) sebum: fungistatic
- antimicrobial peptides
Where on and in the skin are the normal microflora found?
- skin surface
- hair follicle
- sebaceous gland
- sweat gland
Which integumentary system locations have high density of microflora?
- intertriginous skin ( any skin that comes in contact with any other skin)
- more moist
- accumulation of dead skin cells
-scalp
Which integumentary system locations have low density of microflora?
- dry skin
- nails
- outer ear
How do normal microflora of skin help protect us against skin infections
- acids decrease pH
- suppresses pathogens
- competitive exclusion
- microbial antagonism
- microflora consuming nutrients, so pathogen cannot consume them
- secrete bacteriocins (short proteins/peptides> attack other bacteria)
What is the % of people that have S. Aureus…
Nose
Throats
Healthcare workers
Nose and throat: 10% of people in the population
healthcare workers: 30%>
Are all strains of S. Aureus equally pathogenic?
- No
- vary with respect to their ability to cause disease
- some are weak and some have virulence factors
- production of certain toxins
- vary of resistance to antibiotics
What is the function of the enzyme coagulase ?
How would you detect the presence of this enzyme in the lab?
-allows the bacteria to cause inappropriate blood clots
- Coagulase test
- you supply clotting factors; plasma that contains fibrinogen
- Positive test:tube coagulates
Which species test positive and negative for coagulase?
+: S. Aureus
-:S. Epidermidis, S. Saprophyticus. (CoNS)
Describe what a furuncle is
-Staphylococcus infects hair follicle
Describe a non bulbous impetigo
Infection of the skin frequently around the mouth and nose but can occur at any broken skin
-non bullous:crusty yellow fluid from pustules; may be caused by strep
Describe bollous impetigo
-S. Aureus releases proteases (“exfoliating toxins”) that digest anchoring proteins in the epidermis;Bullous result
Describe what a ecthyma is
- deep impetigo, causing skin lesions
- may be caused by Streptococcus
What is the general definition of pneumonia
- when an organism infects the alveoli of the lungs
Virulence factors of S. Aureus
- exfoliating toxin
- coagulase
- leukocidin
- toxin that kills WBC/neutrophils
- Hyalauraonidase
- digests ECM around epithelial cells
- spreads inside the body
- Protein A
- Binds to Fc region of antibody
- Staphylokinase
- activates plasmin (control blood clotting)
-enterotoxin
-toxic shock syndrome toxin
-
S. Aureus food intoxication
Which properties of the Rely tampon contributed to the increase in the number of cases of toxic shock in the late 1970s?
- it changed the environment of the vagina that it promoted the growth of S. Aureus
- Rely were 20x more absorbent that they were able to keep them in for almost a day
- carboxymethylcellulose promoted the growth of S. Aureus
What are superantigens?
- proteins/toxins
- overstimulate immune system
- cross link T cell receptors on CD4 T-cells to MHC2 protein
- cytokine storm (too many cytokines) > toxic shock syndrome
- overstimulate immune system
Name 3 superantigens. Which 2 cause toxic shock or similar syndromes?
Toxic shock syndrome toxins ‘TSST-1’ (S. Aureus) > toxic shock syndrome
Enterotoxin ( S. Aureus) > NVD cramps
Streptococcus pyogenes > Toxic shock syndrome
What are antigens
- molecules/structures that lymphocytes recognize as foreign
- stimulate the adaptive immune system
What are the symptoms of toxic shock syndrome
- decrease in blood pressure
- pulmonary edema
- DIC; microscopic blood clots throughout body uses up clotting factors (coagulopathy)
