LG1.9 Microbiology: Intro to Musculoskeletal Infections – Dr. Pettit Flashcards
What are examples of non-specific defenses of the skin?
1) Physical barrier to infection
2) ~pH 5
3) mostly dry
4) sweat glands
5) salty
6) sebaceous glands
7) fatty acids, wax esters
8) Beta-defensins*
9) Lysozyme
10) Neutrophils, langerhans cells
11) Normal microbiota*
What is a Beta-defensin and what is its function?
β-defensins are cationic peptides and thus can interact with the membrane of invading microbes, which are negative due to lipopolysaccharides (LPS) and lipoteichoic acid (LTA) found in the cell membrane. The peptides have higher affinity to the binding site compared to Ca2+ and Mg2+ ions. The peptides will therefore exchange place with those ions, thus affecting the stability of the membrane. The peptides have a greater size compared with the ions which cause changes in the membrane structure. Due to changes in the electric potential, peptides will pass across the membrane and thus aggregate into dimers. Pore complex will be created as a result of breaking the hydrogen bonds between the amino acids in the terminal end of the strands connecting defensins monomers. Formation of pore complex will cause membrane depolarization and cell lysis.
What are the two leading agents of soft tissue and bone infection?
Staphylococcus aureus and Streptococcus pyogenes
In general which bacteria normally formed a localized abscess?
S. aureus
In general which bacteria normally tends to spread through tissues?
S. pyogenes
What is the most common cause of skin and soft tissue infection in the U.S.?
MRSA
What is cellulitis?
Acute spreading infection of deeper dermis and subcutaneous fat.
What are the most common symptoms of cellulitis?
-Pain, erythema, edema, and warmth
What are other possible (uncommon) symptoms of cellulitis?
1) Regional lymph node enlargement, malaise, chills
2) May progress to sepsis within 24-48 hours
3) Can lead to necrotizing fasciitis, osteomyelitis
What are the main points in the diagnosis of cellulitis?
- Rapid
- Clinical, history
- Can be confirmed by culture
- Specimen is taken from the advancing edge.
What is the treatment for cellulitis?
1) Oral or parenteral empiric antibiotic coverage streptococci, staphylococci until culture results in.
2) Elevate
3) Debridement
4) For more serious or rapid spreading cases, admit and IV antibiotics.
What bacteria most commonly causes necrotizing fasciitis in salt water?
Vibrio vulnificus
What bacteria most commonly causes necrotizing fasciitis in fresh water?
Aeromonas
Which Gram type bacteria is mostly on the skin and why?
Gram positive is normally more common on the skin, this is because they are handle the external environment better than gram negative.
Where does cellulitis normally originate from?
1) Skin lesions (Boils, ulcers, and tinea pedis)
2) Trauma
