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What are the defenses of the skin?
- Intact physical barrier to infection
- Cool
- pH around 5(Acidic)
- Dry
- salty sweat glands
- sebaceous glands – fatty acid, wax, esters
- beta defensins
- lysozymes
- neutrophils, Langerhans cells
- normal microbiota
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What is beta defensins?
It is one of the nonspecific defenses of the skin, these are cationic peptides that form pores in membrane of microbes
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Which are the two heavy hitter bacteria that cause bone and soft tissue infections?
- Staphylococcus aureus
- Streptococcus pyogenes
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Which is the most common cause of skin and soft tissue infection in the U.S?
MRSA
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What is the pattern of Staphylococcus aureus abscess formation?
Localized collection of pus surrounded by inflamed tissue
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What is the characteristic of Streptococcus pyogenes infection?
Spreads through tissues
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What are the most common etiologies for subcutaneous fat cellulitis?
- Streptococcus pyogenes
- Staphylococcus aureus
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Which is the most susceptible group of people getting infected by Kingella kingae?
Toddlers
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Which is the most susceptible group of people getting infected by S.aureus?
Elderly
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What is the bacteria in freshwater necrotizing fasciitis?
Aeromonas
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What is the bacteria in saltwater necrotizing fasciitis?
- Vibrio vulnificus
- What are the common physical causes that leads to cellulitis?
- Superficial skin lesion
- Trauma
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What are the symptoms of cellulitis?
- Pain
- Erythema
- Warmth
- Edema
- Indistinct border
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Cellulitis may progress to sepsis within ____ hours.
24-48
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True/False: Cellulitis often have systemic symptoms such as malaise, chills, lymphadenopathy?
False; systemic symptoms are possible but not common
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True/False: cellulitis can lead to necrotizing fasciitis and/or osteomyelitis?
True
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Cellulitis are more commonly seen in which part of the body?
Lower extremities
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What is the best treatment for cellulitis while waiting for culture result?
Treating empirically for S.aureus and S.pyogenes
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What are some treatment methods for cellulitis?
- Empiric antibiotic
- Elevation
- Debridement
- Hospital admission and IV antibiotics
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What is one distinguishing factor that differentiates S.aureus from other gram + cocci?
Coagulase positive
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What kind of hemolysis does S.aureus do?
Beta hemolysis = lysing RBC
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What is a unique metabolic function that S.aureus can do?
Mannitol fermentation
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What is the main difference between Streptococci and Staphylococci?
- Streptococci are catalase negative
- Staphylococci are catalase Positive
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Where are the most common places that S.aureus found in the body?
Nose, skin and mucous membranes
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True/False: S.aureus are facultative anaerobes?
True
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What would be a result of coagulase test run for S.aureus?
Positive; this indicates that there is fibrin formation
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Which structural component of S.aureus contribute to phagocytosis?
Capusl
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Which structural component of S.aureus contribute to binding to mucosal cells and tissue matrices of host?
Fibrinogen, elastin-binding proteins
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Which structural component of S.aureus contribute to anti-opsonic abilities (Ig-mediated clearance)?
Protein A
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Which structural component of S.aureus contribute to WBC chemoattractant?
Peptidoglycan
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Which toxins of S.aureus affect many human cell types?
Alpha hemolysin : pore formation
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Which toxin of S.aureus affect neutrophils?
PVL (contribute to puss)
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Which enzyme of S.aureus converts fibrinogen to fibrin?
Coagulase
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Which enzyme of S.aureus help it to spread through our tissues?
Hyaluronidase, lipase, nuclease, protease
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Which enzyme of S.aureus dissolve fibrin clots?
Fibrinolysin
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What is one component that is shared by all methicillin-resistant S.aureaus (MRSA)?
Staphylococcal cassette chromosome mec (SCCmec) that encodes the MecA gene that alters a transpeptidase which is a penicillin binding protein
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What is the result of an altered transpeptidase protein in MRSA?
Broad spectrum Beta lactam (antibiotic) resistance
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Which group do Eikenella corrodens and Kingella kingae belong to?
HACEK group
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What is the shape of Eikenella corrodens and Kingella kingae?
Gr NEGATIVE. Bacilli to coccobacilli pleiomorphs
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How fast do HACEK group grow?
Fastidious, slow-growing (but could grow with carbon dioxide, hold blood plates for 7 days)
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What is the main difference between Kingella and Eikenella?
- Kingella has capsule and Beta-hemolysin
- Kingella is the leading cause of septic arthritis, osteomyelitis in children 4 years under
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What is the shape of Nocardia and Actinomyces?
Gr POSITIVE. Filamentous rod
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Where is Nocardia most likely found?
In the environment, not microbiota. I.e. Soil, plants, water
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How fast do Nocardia grown?
Slow
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What is the characteristic of Nocardiosis?
Necrosis, abscess formation, granulomas
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What is the most common way of getting infected with Nocardiosis?
Pulmonary inhalation especially in immunocompromised patients
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What is the likely source of cutaneous Nocardiosis?
Traumatic introduction such as a thorn
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What is an example of cutaneous Nocardiosis?
Mycetoma
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How would a culture of Nocardia appear?
Aerial filaments
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What is necessary in order to treat nocardiosis?
Debridement before antibiotics
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Where could Actinomyces be found in humans?
Normal microbiota in oropharynx, intestines and GU
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What is a characteric of Actinomyces isarelii?
Molar tooth colonies
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What disease does Actinomyces israelii commonly cause?
Actinomycosis
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What are the common forms of acitnomycosis?
- Cervicofacial (most common, about 50% of cases; male affected 3:1)
- Thoracic
- Abdominal
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What is the hallmark of actinomycosis?
- Spread without regard to anatomical barrier
- Sulfur-colored granules
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What are the risk factors for cervicofacial actinomycosis?
- Tooth decay
- Dental operation
- Face trauma
- Diabetes/ immunosuppression
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