Flashcards in Ch1: Skin Deck (276):
Pathogens usually enter the lower layers of epidermis and dermis after what?
Pathogens can infect the follicle how?
Descending from surface of skin
Pathogens can also infect subcutaneous and dermis how?
Leaving the blood
Function of the skin is to do what? (6)
1. Protect from environment
4. Temp regulation
5. Blood pressure
6. Synthesize Vitamin D
Normal skin flora inhabit what areas predominately?
Moist: groin, armpits
What are the most common genera of skin flora? 2
1. Staph epidermidis (100% of pop)
2. Staph aureus (20% of pop)
Host defenses of the skin include?
1. Stratum corneum: Sloughed cells carry microbes away
2. Low moisture = fewer microbes
3. Salty sweat = discourage growth
4. Sebum = decreases pH --> discourage growth
5. Hair follicles = Produce lysozyme
6. Lower temperature = discourage growth
7. Langerhans cells = APC's of skin
8. Innate immunity
What are the two steps for inflammation of the skin? (2)
What happens in recognition?
Bacterial components such as peptidoglycan, LPS, and other PAMP's are recognize by Toll-like receptors that cause release of inflmmatory cytokines
What happens in recruitment?
Effector cells are recruited to the site of infection by cytokines
What is the effect of cytokines on blood capillaries?
Dilates them -->
1. WBC's recruited
2. Leakage of plasma --> Redness
Why does an inflammation cause pain in the skin?
Due to high density of nerve endings in the skin, swelling causes pain
What is pus formed from? (2)
2. Lysis of foreign things
Viscosity of pus is due to what?
What does TLR-4 recognize?
LPS from gram-negative bacteria
Infections of the skin are of what 3 categories?
Breach in skin
What is a macule?
Circumscribed change in skin color that is NOT raised
What is a papule?
Does it have liquid?
Solid elevated lesion with raised edges
Yes and No.
What is a pustule?
Circumscribed raised cavity containing pus
What is a abscess/boil?
Localized inflammation with pus
What is a furuncle?
Acute, deep-seated red hot nodule or abscess
What is a carbuncle?
Where are they normally found?
Deeper-seated composed of interconnecting abscesses/boils in subcutaneous fat
Neck and upper back where skin is elastic
What two lesions of the skin have pus?
What is pus due to?
Pustule and Abscess/boil
What is staphylococci's shape?
Spheres in clusters (Grape-like)
What is the test for staphylococcus?
Staph aureus secretes what enzyme?
What does coagulase do?
Converts fibrinogen to fibrin
How does the coagulase test work?
Bacteria sample is suspeneded in tube with rabbit plasma, if the bacteria has coagulase produced, a clot will form due to fibrin formation
What does the aureus mean in staph aureus?
Gold, which i the color of colonies
Is staph aureus gram positive or negative?
Size of staph aureus?
1.0 um in diameter
What is the habitat of staph aureus?
1. Human skin
2. Anterior nares
4. hands and fingers
5. Arms and groin
What percentage of human population is colonized with staph aureus?
Transmission of staph aureus is through what?
1. Direct contact
What are fomites?
Objects that can transmit an organism
What does endogenous mean?
Part of normal flora, but can accumulate or go somewhere they shouldn't
What is a virulence factor?
Something that can promote disease
What are the two cell-associated virulence factors of staph aureus? (2)
1. Polysaccharide capsule
2. Protein A
Function of polysaccharide capsule?
Surrounds the bacteria and acts as an anti-phagocytic
Function of protein A?
binds the FC portion of IgG antibodies (including those directed towards itself) which inhibits antibody-mediated phagocytosis
Where is Protein A exactly?
On cell wall and linked to PTG
What are the two secreted virulence factors of staph aureus?
What is exfoliatin?
Protease that degrades desmosomes of tight junctions between cells in epidermis
What does exfoliatin cause? (2)
1. Scalded skin syndrome
2. Bullous impetigo
Genes encoding S. aureus superantigens are located where?
What type of transfer does this allow for?
In mobile genetic elements such as bacteriophage and pathogenicity islands
Do all staph aureus species have the same superantigens?
No, different isolates have different compositions
Superantigens bind to what? 2
Simultaneously to the MHC class II molecule on surface of APC's and the T-cell receptor
Result of superantigens binding to APC and T cell?
Non-specific stimulation of T cells (2-20%) resulting in excessive cytokine release leading to to fever, hypotension, rash and a variety of other clinical manifestations
What is the most common and important superantigens?
What does it cause?
Toxic Shock Toxin-1 (TST-1)
Toxic Shock Syndrome
Fever, Hypotension, Shock
What are the two categories of staph infections?
What does bacteria disease of staph do?
The bacteria invades and evokes clinical manifestations
What does toxigenic disease of staph mean?
Clinical manifestations are due to staph toxin only
Skin diseases of staph?
What is impetigo?
Infection of epidermis leading to bullous impetigo
What is foliculitis?
Infection of hair follicle
What is a stye?
Folliculitis in eye
What are the three main bacterial versions of staph infection?
1. Skin diseases
2. Wound Infection
What can cause bacteremia? (4)
1. Ruptured abscess
What can staph cause once in the blood? 4
Three forms of toxigenic disease from staph aureus?
1. Scalded skin syndrome
2. Bullouis impetigo
3. Toxic shock syndrome
Scalded skin syndrome is due to what?
What does the exfoliatin toxin do uppon reaching the blood?
Spreads out and degrades desmosomes of epidermis --> Top layer of epidermis to be released
Complications of SSS? 2
1. Fluid loss
2. Secondary infections of skin
How does scalded skin syndrome appear?
What population gets it?
Burn or blister
Neonates and children
How do you diagnose SSS? 2
1. Patient history
What is bullous impetigo?
What causes it?
Toxic shock syndrome is caused by what?
Superantigens that nonspecifically stimulate cytokine production.
Most potent superantigen of s. aureus?
What can it cross that other superantigens can't?
Cross mucal membrane
TSS is based on what 4 features?
1. Fever greater than 102
2. Hypotension less than 90 mmHg
4. Abnormalities in 3 organ systems
Two types of TSS?
Describe menstrual TSS.
S. aureus that normally colonizes the vagina grows to greater numbers during menstruation --> Produced superantigen (mainly TST-1) --> Crosses mucosa --> Enters blood --> Causes symptoms of TSS
Increased growth of s. aureus during menstruation is due to what? (3)
1. Increase supply of nutrients in vagina
2. Increase in pH of vagina
3. Drying of vaginal mucosa by highly absorbent tampons leading to tears in epithelium
TST-1 production in menstrual TSS is enhanced by what?
Presence of synthetic fibers used in tampons
What is non-menstrual TSS? 2
1. When superantigens produced by S. aureus colonizaiton of skin/wounds enters the bloodstream to cause systemic effects
2. S. aureus is present in bloodstream and produces superantigens.
Non-menstrual TSS is associated with what? 4
2. Post partum
3. Barrier contraceptives
4. Cutaneous infections
What are the two tests to run when diagnosing potential staph aureus?
1. Gram-stain = Positive
2. Coag test = Positive
S. aureus grows well on what medium?
Mannitol salt agar is useful for what reasons in testing for staph aureus
1. Selective: Selects ability of staph to grow in high salt environment
2. Differential: S. aureus can ferment mannitol causing pH indicator to turn yellow
Why is culturing so important with staph aureus?
Have to determine degree the strain has resistance to different antibiotics
Treatment of skin lesions of staph aureus includes what?
Incision and drainage with or without mupirocin or additional antibiotics
What does antibiotic use against s. aureus depend on?
1. Speed lesion is progressing
2. Systemic symptoms
3. extremes of age
What percentage of staph aureus is resistant to penicillin?
Produce a penicillinase which degrades penicillin
MRSA is an isolate that is resistant to what?
All penicillinase-resistant Beta-lactam antibiotics: Methicillin, oxacillin, floxacillin
Resistance to methicillin-like antibiotics is associated with what?
What is this?
Mobile DNA element that encodes a penicillin binding protein that is NOT activated by methicillin like antibiotics
Due to the significance of MRSA how do we designate s. aureus?
MRSA = Resistant
MSSA = Sensitive
Is hospital acquired MRSA different from community acquired?
They are different genetically, and HA-MRSA is more resistant to antibiotics
Which of the two, HA-MRSA and CA-MRSA is a recently emerged infectious agent?
CA-MRSA have what gene?
CA-MRSA can have what effects in addition to normal s. aureus? (3)
1. Necrotizing fasciitis
2. Purpura fulminans
3. Necrotizing pneumonia
Treatment of CA-MRSA is most effective when?
If the antibiotic sensitivity of the organism is determined.
In severe cases in which MRSA is suspected, what antibiotics are used? 3
CA-MRSA requires what to be accurately treated?
Multiple sampling for > 90% sensitivity
Treatment of CA-MRSA depends on what? 2
1. Severity of disease
2. Local susceptibility data
What is VISA?
Vancomycin-intermediate resistant staph aureus
VISA produces what anatomically?
Thicker cell wall of PTG that decreases vancomycin's ability to weaken cell wall
What is VRSA?
Vancomycin-resistant staph aureus
VRSA has what genetic advantage?
What does this do?
Where did it get it from?
Modifies structure of PTG making it not susceptible to vancomycin
VanA VRSA have what protein change?
D-ala D-lac in PTG crosslinking instead of D-ala, D-ala
What vaccine exists for staph aureus?
What does the word streptococci mean?
Streptus = Pliant
Cocci = Berry
How does strep stain in a gram stain?
Two special shape characteristics of strep?
2. Cell division occurs in one plane --> Chain
How does strep react in a catalase test?
Catalase = Negative
Is strep an anaerobe or aerobe?
Do they tolerate O2?
Two ways to classify strep?
Describe the hemolysis classification of strep
Beta strep: Complete cleaning around colony
Alpha: Partial clearing (green)
Gamma: No hemolysis
What is hemolysis of strep performed on?
Agar plates with blood
What is lancefield classificaiton based on?
Presence of different carbohydrates in the cell walls of different strep species
How many species are in Group A and Group B strep?
Essentially one each
What is the Group A strep?
What is group A streps
Appearance similar to?
Similar to other beta-hemolytic
Habitat of s. pyogenes?
Human mucosal surfaces
What other organisms can s. pyogenes inhabit?
Transmission of s. pyogenes is how? 2
Cell associated Virulence factors of S. pyogenes? 2
1. Polysaccharide capsule
2. M protein
The polysaccharide capsule is comprised of what in s. pyogenes?
Is it antigenic?
Is it similar to hyaluronic acid in our bodies?
Identical to hyaluronic acid in our bodies
What is it called when s. pyogenes avoids detection by using the same hyaluronic acid as in humans?
The M protein of s. pyogenes is where?
Embedded in cell wall
How many serotypes of M protein exist?
Does an antibody against one serotype protect against other serotypes?
What is the M protein's 100 serotypes an example of?
The M protein has what function? 2
1. Inhibits phagocytosis
2. Allows GAS to adhere to human epithelial cells
What is the most important virulence factor of GAS?
What are the five secreted virulence factors of GAS?
1. Streptolysin O
What does streptolysin O do?
It is a pore-forming toxin that lyses eukaryotic cells
How is streptolysin O seen diagnostically?
It is responsible for Beta-hemolysis
What form is streptolysin O in?
An elevated antibody titer to streptolysin O (ASO test) indicates what?
1. Recent strep pyogenes pharyngeal infection, but not skin infection.
2. Rheumatic fever
How many types of DNAses does s. pyogenes release?
Four (A, B, C, D)
DNAses are secreted into human host to do what?
Degrade nucleic acids present in Neutrophil Extracellular Traps, a part of innate immunity
An elevated antibody titer to DNAse B suggests what? (2)
1. S. pyogenes skin infection recently
2. Post-streptococcal glomerulonephritis
What does protease do? (2)
What is it also known as?
1. Degrades human proteins
2. Promotes tissue invasion
Streptokinase has what function?
Activates plasminogen to plasmin
Plasmin can activate what? 3
3. Proteins involved in tissue repair
Human plasmin can also bind to the surface of bacterium to do what? (2)
1. Degrade tissue
2. Promote dissemination
What are the superantigens in strep pyogenes called?
Streptococcal pyrogenic exotoxins
SPE's are encoded by what?
Streptococcal superantigens function how?
Same as superantigens in staph
What is impetigo?
Infection of epidermis caused by S. pyogenes, S. aureus, or both
What is erysipelas?
Infection of dermis
What is cellulitis?
What typically causes it?
Infection of dermis and/or cutaneous tissue
1. S. pyogenes
2. S. aureus
What are some Characteristics of cellulitis?
1. Might be able to culture the bacteria
2. Lymph nodes are swollen
3. Fever, chills, malaise
4. Infection can progress rapidly --> Sepsis
Which has a more clear demarcation, erysipelas or cellulitis?
what is necrotizing fasciitis?
Infection of subcutaneous CT and fascia with myonecrosis
What can cause necrotizing fasciitis? 4
1. S. pyogenes
3. Clostridium perfringens
4. Aeromonas hydrophila
Where does necrotizing fasciitis typically begin?
Site of trauma
Symptoms of necrotizing fasciitis?
What antibiotic works well against necrotizing fasciitis?
Foot/limb infections in diabetic patients are typically caused by what?
Mixed infections of s. aureus, s. pyogenes, pseudomonas, enterobacteriaceae
Diabetic neuropathy is due to what?
What is post infection sequelae?
Disease that occurs after primary infection
Can post-infection sequelae occur even if the microbe has been eliminated?
Post-infection sequelae is caused by what?
Misdirected immune response to microbe
S. pyogenes infection precedes what three post-infection sequelae?
What type of infection does each follow?
1. Post-streptococcal acute glomerulonephritis (PSAGN): Skin
2. Acute rheumatic fever/heart disease: Pharyngeal
3. Pediatric autoimmune neuropsychiatric disorders: (Pharyngeal)
What happens in PSAGN
Antibody-antigen complexes are deposited in glomerula of kidney causing inflammation and damage
Laboratory diagnosis of s. pyogenes shows what in
1. Gram stain
2. Blood-agar culture
1. Gram positive
3. Catalase negative
4. Group A
To obtain evidence of a recent s. pyogenes skin infection determine what?
Levels of antibody titer against streptococcal DNAseB
What is drug of choice for s. pyogenes?
What else works? (3)
Amoxicillin, Erythromycin, Cephalosporins
Why is erythromycin used sometimes instead of penicillin?
Avoid allergic responses to penicillin
Is there a vaccine for s. pyogenes?
what are the two most important gram positive spore formers?
What does clostridium perfringens cause?
4 main features of gas gangrene?
1. Gram positive
2. Bacillus shape
3. Forms endospores
Habitat of clostridium perfringens? (4)
1. GI tract of animals
How does one make sure to be rid of clostridium perfringens on fomites?
How is c. perfringens transmitted?
Exogenously or endogenously
Two clinical infections of c. perfringens?
Traumatic gas gangrene
Spontaneous/Nontraumatic gas gangrene
Traumatic gas gangrene results from what?
Contamination at site of trauma (cut, gun shot, puncture wound) with spores that germinate to initiate infections.
How does trauma facilitate better growth of c. perfringens?
Trauma --> Decreased tissue oxygenation
Spontaneous/nontraumatic gas gangrene occurs in patients with what?
Tissues lack adequate oxygen
Diabetes, colon cancer, atherosclerosis
Since c. perfringens is an anaerobe, it ferments, thus producing what?
H2S that stinks and you can see the gas
Laboratory diagnosis of c. perfringens? (2)
1. Gram positive rods in fluid from infected area
2. Nagler's reaction
How does Nagler's reaction work to test for c. perfringens?
Since c. perfringens secretes a lecithinase, when it is grown on agar plate with lecithin (egg yolk), it will degrade the lecithin and form a zone of opacity.
Treatment of c. perfringens? (3)
1. Prompt surgical remova of dead, damaged, infected tissue
2. Amputation if necessary
3. Antibiotics (penicillin)
IV drug users can insert drugs how? 3
1. Using contaminated needles
2. Not disinfecting skin
3. Injecting drugs contaminated with microbes
Is propionibacterium acnes part of normal flora?
What type of bacteria is propionibacterium acnes?
Habitat of propionibacterium acnes?
Sebaceous glands of skin because there is not much oxygen and sebum provides nutrients
End product of propionibacterium acnes eating sebum? (3)
1. Fatty acids
Transmission of propionibacterium acnes?
Inflammatory acne is due to what?
Bacterial infection, and mainly propionibacterium acnes
What are the sebum channels called?
What must happen to pilosebaceous ducts for propionibacterium acnes to grow well?
Duct has to get clogged so that bacteria are not washed out to surface of skin.
Hormonal changes associated with puberty may result in acne why? (2)
1. Increased sebum production
2. Increased keratinizaiton
Treatment of propionibacterium acnes? (4)
1. Benzoyl Peroxide
What does benzoyl peroxide do?
Generates O2 as it breaks down in skin --> Inhibits propionibacterium acnes growth
What do retinoids do?
Inhibit sebum production
Burns have what two main effects on skin?
1. Damage physical barrier of skin
2. Diminish neutrophil function
Minimizing colonization of burn involves what?
Topical antimicrobials like silver nitrate
Most important pathogens involved in burn wounds? (3)
1. Pseudomonas aeruginosa
2. Staph aureus
3. Strep pyogenes
Physical treatment of burn? (2)
1. Surgical debridement to decrease bacterial numbers
2. Different forms of silver to inhibit microbes
Antibiotic treatment of burns?
Whatever antibiotic is best for the specific agent
Pediatric burn patients are more susceptible to what? 2
2. Toxic shock syndrome
S. aureus and x. pyogenes
Pseudomonas aeruginosa is seen in what clinical infection setting?
Pseudomonas aeruginosa can cause what? (3)
2. External otitis
3. Hot tub rash/itch
What is pyoderma?
Infection of epidermis
What is external otitis?
Infection of external auditory canal
Pseudomonas aeruginosa is diagnosed how in the lab?
1. Using Woods lamp with UV light to see fluorescein which is produced by Pseudomonas aeruginosa
2. Culture from blood or skin
Treatment of vaccine for Pseudomonas aeruginosa?
Is Pseudomonas aeruginosa very resistant to antibiotics?
Yes to many common ones
Leprosy is called by what?
Characteristics of Mycobacterium leprae? 5
1. Acid fast positive
3. Grows best at 30 degrees Celsius
4. Can not culture on solid media
5. grows on armadillo
Habitat of Mycobacterium leprae? (3)
Is Mycobacterium leprae a zoonotic disease?
No, have to get from another human
How is Mycobacterium leprae transmitted?
Mycobacterium leprae has a predilection for what type of cell?
What does Mycobacterium leprae do upon entering body?
Invades schwann cells, tissue macrophages, and endothelial cells --> Granuloma formation
What special distinction does Mycobacterium leprae have?
Only bacteirum known to damage the peripheral nervous system
Two states of leprosy?
Symptoms of tuberculoid leprosy?
Regions of skin lose sensation due to nerve damage from immune response --> injury and secondary skin infection
What limits the infection in tuberculoid leprosy?
What gets activated?
How much bacteria is in skin and nose?
Cell mediated immunity
Very little, due to CMI response
What does the tubercle mean in tuberculoid leprosy?
Granuloma containing M. tuberculosis has formed which indicates an effective immune response
Is the person very infectious in tuberculoid leprosy?
Lepromatous leprosy refers to a disease state of what?
When CMI response is ineffective.
Are you safe if lepromatous leprosy skin test comes back negative?
Bacteria in lepromatous leprosy grow where?
Skin and peripheral nerves --> Not contained by immune system
which form of leprosy is most contagious?
Diagnosis of Mycobacterium leprae? (2)
1. Acid fast test on nose, lesion, and earlobe biopsies
2. Lepromin test
What is lepromin test?
Extract of Mycobacterium leprae
Antibiotics for Mycobacterium leprae? 3
Dapsone (folic acid synthesis)
Mycobacterium marinum is endemic where?
How is mycobacterium marinum commonly called?
Fish tank or swiming pool granuloma
Initially where does M. marinum infect?
Visibly looks how to start?
Progresses to what?
Skin at sites of minor trauma
After 2-8 weeks looks like papule
Becomes suppurative ulcer
Mycobacterium ulcerans is endemic where?
Infections occur where?
Sign of disease?
Africa and australia
Sites of trauma
Painless ulcerative lesions
Mycobacterium tuberculosis colonizes skin how? (2)
1. Usually hematogenous dissemination
2. Direct inoculation can occur
How does m. tuberculosis look clinically?
Papule --> Painless ulcer
Superficial mycoses include what?
Pityriasis versicolor or tinea versicolor
What causes pityriasis versicolor/tinea versicolor?
Is malassezia furfur a normal flora of skin?
How does its lesion appear?
Is it contagious?
Well-demarcated with scaling patches of different color
Melanin synthesis disrupted
KOH wet mount of a malassezia furfur appears how?
Spaghetti and meatball yeast forms
Dermatophyte infections involve organisms that do what?
Dermatophyte infections are spread by what?
What are the three dermatopyte species?
Dermatophytes invade what structures? 3
How can dermatophytes be clinically diagnosed? (2)
1. Fluoresce under UV light
2. Grow on sabouraud's agar
Symptom of dermatophytes?
Dermatophyte infections are treated how?
Do they disseminate?
Tinea means what?
What causes it?
What is tinea capitis?
Ringworm of scalp and hair
Is tinea capitis infectious?
What is important for transmission?
Most common causes of tinea capitis?
Microsporum (most likely)
What is tinea cruris?
What is common cause? 2
What is tinia pedis?
What is common cause?
Candida species cause what two skin manifestations?
2. Diaper rash
Candida albicans require what for growth?
Subcutaneous mycoses is caused the most by what in the US?
Sporotrichosis is a noedular condition caused by what?
Sporothrix schenckii is seen where? (3)
2. Thorned plants (gardeners)
3. Sphagum moss
Sporotrichosis enters body how?
Skin breaks and then follows lymphatics
Systemic mycoses that can manifest in the skin include? (4)
histoplasmosis, and cryptococcosis.
The systemic mycoses are initiated how?
Inhaled and then disseminate in blood
Reactive arthritis is also known as what?
What happens in this disease?
Additional symptoms? (2)
Microbe --> Autoimmune response --> Inflamed joints
Conjunctivitis and urethritis
Common bacterial causes of reactive arthritis? 5
Septic arthritis is caused how?
Circulating bacteria in the blood localizes in a joint or bacteria gains access to join through skin.
Fever, pain, swelling
How do you diagnose septic arthritis?
Culture synovial fluid and blood
Common ways to pick up septic arthritis? 2
Common bacterial causes of septic arthritis?
Treatment of bacterial arthritis? 2
Antibiotics and Drainage
Osteomyelitis is what? 3
Bone infection by an adjacent infection (direct), orthopedic surgery, hematogenously
Symptoms of osteomyelitis? (2)
1. Pain at site
Diagnosing osteomyelitis? (2)
Osteomyelitis is treated how? 2
Common bacterial causes of osteomyelitis?
Which type is common in newborns?
Which type is common in sickle cell?
S. aureus: newborns
Coag negative staph
Salmonella: Sickle Cell
Treatment of osteomyelitis?
1. Identify bacteria and resistance through needle aspiration and culture
Antibiotic therapy lasts how long for osteomyelitis?
Transmission of infective endocarditis?
Hematogenous: Circulating microbes bind to valves
Guaranteed symptoms of infective endocarditis? (2)
3. Heart murmur
Endocarditis is categorized in what two ways?
What type of bacteria
Acute: Virulent bacteria like Staph Aureus
Chronic: Less virulent: Strep viridans
Viridans strep describes what group?
Strep that lives in oral cavity normally
Viridans strep regularly enter bloodstream when? 3
1. Tooth brushing
3. Dental procedures
What type of heart do the less virulent strep viridans infect?
What is the mortality of infective endocarditis with treatment?
With no treatment?
What is the diagnosis criteria for infectious endocarditis?
What is required? (3)
1 major and 3 minor
Major criteria for infectious endocarditis? 2
1. More than one positive blood culture
2. Evidence of myocardial involvement
Minor criteria for infectious endocarditis? (6)
1. Predisposition (Rheumatic fever, IV drug use)
3. Vascular problems (Emboli, bleeding)
4. Immunological problem (glomerulonephritis)
5. One positive blood culture
6. Echocardiographs consistent with endocarditis
What is most important test for diagnosing infective endocarditis?