Skin Infections

  1. Risk factors for skin and soft tissue infection
    • damage to corneal layer (puncture, scrape, abrasion)
    • excessive skin moisture (allows for organism growth, including gram-negatives)
    • poor hygiene
    • ingrown hairs
    • inadequate blood supply
    • underlying diseases (DM, obesity, malnutrition, IVDU, immunosuppression)
  2. Epidermis (stratum corneum)
    • consists of flattened, cornified cells
    • skin cells get renewed
    • shedding of skin cells
  3. Dermis
    • connective tissue
    • blood vessels
    • lympathics
    • sensory nerve endings
    • sweat & sebaceous glands
    • hair follicles
  4. Subcutaneous layer
    • fat (adipose) tissue
    • * underneath SQ layer is fasica: which separates skin from underlying muscles
  5. Infection Normally Resistant to Skin and Soft Tissue
    • dry surface is not conducive to bacterial growth
    • epidermal layer is continuously renewed
    • sebaceous secretions hydrolyed to free fatty acids that inhibit growth
  6. Linezolid
    • MOA: inhibits protein synthesis at the initiation stage binding to 30S and 70S ribosomal subunits
    • bacteriostatic: to enterococci, staphylococci
    • bacteriocidal: to streptococci
  7. Clindamycin
    • bacteriostatic
    • AVOID: co-administration w/macrolides
  8. Tetracyclines and Glycyclines
    • binding to 30S ribosomal subunit
    • tetracycline inhibit protein synthesis
  9. Mupirocin
    • pevents isoleucine into bacterial proteins affecting protein and RNA synthesis
    • bacteriostatic: at low concentrations
    • bacteriocidal: at high concentrations
    • administered topically
  10. Retapamulin
    selectively inhibits bacaterial protein synthesis by interacting at 50S subunit of bacterial ribosome
  11. Sulfonamides
    • inhibit enxyme dihydropteroate synthase which is needed for biosynthesis of folic acid
    • by competitively inhibiting enzyme reactions involving PABA
    • PABA is needed to produce folic acid and tetrahydrofolic acid
  12. Trimethoprim
    • inhibits biosynthesis of folic acid and results in blockage of DNA base synthesis
    • also inhibits enzyme dihydrofolate reductase which is responsible for reduction of folic acid to tetrahydrofolic acid
  13. Risk factors for Folliculitis
    • shaving
    • wearing tight clothes
    • exposure to topical ointments (causes skin moisture)
  14. Microbial cause for Folliculitis
    • S. aureus
    • Pseudomonas aeruginosa (if exposed to water)
  15. Treatment for Folliculitis or Stye
    • local, warm compress promoting drainage
    • Unresponsive to local treatment: drugs
    • clindamycin
    • erythromycin
    • mupirocin
  16. Microbial cause for Furuncle and Carbuncle
    • S. aureus
    • S. pyogenes (B - hemolytic streptococci)
  17. Treatment for Furuncle
    • moist heat (small furuncles)
    • incisions (larger furuncles)
    • CA-MRSA: bactim (most common), doxycycline, clindamycin, linezolid
    • Streptococci: add amoxicillin for coverage for empiric
    • VRE: linezolid (due to expense)
    • Pencillin allergy: clindamycin
    • Streptococci (non-purulent): dicloxacillin, cephalexin (1st gen cephalosporin)
  18. Erysipeals
    • affects upper dermis and superficial lymphatics
    • fiery red
    • edematous
    • painful lesions
    • affects lower extremities and face
  19. Microbial causes of Erysipeals
    • S. pyogenes (b-hemolytic, strep) *most common
    • S. agalactiae (b-hemolytic, Group B strep)
    • S. aureus
  20. Treatment for Erysipeals
    • penicillin VK
    • penicllin allergy: clindamycin, erythromycin
    • Severe cases: IV penicillin G
  21. Impetigo
    • superficial skin infection
    • small clear fluid-filled vesicles later transform into pus-filled blisters
    • common in children in hot, humid weather
  22. Microbial causes of Impetigo
    • Bullous form: S. aureus
    • Non-Bullous: S. aureus and S. pyogenes (mixed infection)
  23. Treatment for Impetigo
    • usually resolves spontaneously
    • treat symptoms: mupirocin, retapamulin
    • Not responding to treatment: dicloxacillin, cephalexin
    • penicillin allergy: clindamycin
    • retapamulin: treats impetigo caused by MSSA or S. pyogenes
    • Mupirocin: activity against MSSA, MRSA, S. pyogenes
  24. Risk Factors for Cellulitis
    • IV Drug Use
    • DM
    • procedures that alter lymphatic drainage/compromise lymphatic circulation (post-mastextomy, post saphenous vein removal)
  25. Microbial causes for Cellulitis
    • S. pyogenes
    • S. aureus
  26. Treatment for Cellulitis
    • adjunctive therapy: NSAID
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  27. Necrotizing fasciitis
    • destruction of SQ fat and fascia
    • Type I: slower-progressing infection, polymicrobial (1 anerobe and 1 aerobic)
    • Type II: caused by S.pyogenes, flesh-eating bacteria
    • clostridial myonecrosis: infection deeper into skeletal muscle, caused by Clostridium perfringens
  28. Treatment for Necrotizing Fasciitis
    • surgery
    • adjunctive therapy: antibiotic w/surgery
    • carbapenem: imipenem/cilastatin, doripenem, meropenem, ertapenem
    • cefotaxime + metronidazole
    • piperacillin/tazobactam
    • penicillin allergy: metronidazole, clindamycin + aminoglycoside OR metronidazole, clindamycin + fluoroquinolone
  29. Type II Necrotizing Fasciitis
    • S. pyogenes or clostridium perfringens myonecrosis treatment is: penicillin + clindamycin
    • adjunctive therapy for clostridium myonecrosis: hyperbaric chamber
  30. Risk Factors for Diabetic Foot Infection
    • neuropathy peripheral vascular disease/ poor blood flow
    • immunologic defects
  31. Microbial causes of Diabetic Foot Infection
    • aerobic gram (+): S. aureus, streptococci enterococci
    • aerobic gram (-): pseudomonas
    • anaerobe: B. fragilis
  32. Microbial causes for animal bites
    • Pasturella multocida (most common)
    • streptococci
    • staphylococci
    • Moraxella
    • Neisseria
  33. Treatment for animal bites
    • amoxifillin/clavulanate (most common)
    • doxycycline (2nd line)
    • AVOID b/c poor activity against pasturella mulocida: 1st gen cephalosporin, macrolides, clindamycin
    • IV options: ampicillin/sulbactam, cephamycin, cefotetan, carbapenem
  34. Microbial causes for Human Bites
    • Viridans streptococci
    • S. pyogenes
    • S. aureus
    • Eikenela corodens
    • anerobes
  35. Hematogenous OM
    • infection of bone spread through bloodstream
    • occurs in pts <16 yrs
    • Vetebral osteomyelitis if occurs in adults
    • Microbial causes: S. aureus (most common), S. epidermis (pts w/ protheses), P. aeruginosa (IVDU or near water)
  36. Contiguous OM
    • infection of bone from adjacent soft tissue infection
    • pts >50yrs
    • Microbial causes: S. aureus, S. epidermidis, P.aeruginosa, E. coli, anaerobes
  37. OM secondary
    • secondary to peripheral vascular diesase occurs in pts w/DM
    • >50yrs
  38. 2 main types of Inectious Arthritis (IA)
    • gonocooal arthritis: caused by Neisseria gonorrhoeae
    • rash and multiple joints (polyarticular)
    • nongonococcal arthritis: caused by S. aureus
  39. Risk Factors for OM
    • poor circulation
    • recent injury (broken bone that breaks skin or deep puncture wound
    • orthopedic surgery
    • IVDU
  40. Risk factors for IA
    • systemic corticosteroid use
    • pre-existing inflammatory arthritis
    • DM
    • prosthetic joint
    • unprotected sex
  41. 4 criteria diagnosis for lower extremity OM
    • ulcer area >2cm
    • positive probe-to-bone test
    • ESR >70
    • abnormal x-ray
  42. Treatment for OM
    • Use IV: unless pt does NOT have DM or PVD then can switch later to oral therapy
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  43. Treatment for IA
    • 3 components of treatment: antibiotics, joint drainage, joint rest
    • N. gonorhoeae: ceftriaxone, doxycycline (penicillin allergy)
    • after 3days of IV: amoxicillin, doxycycline, tetracycline
    • S. aureus: treat MSSA and MRSA
    • MSSA - nafcillin, cefazolin, ceftriaxone, clindamycin
    • MRSA - vanco, dapto, linezolid
  44. Inhibition of Bacterial Cell Wall Synthesis
    • B-lactams
    • Vancomycin
    • Telavancin
  45. Inhibition of DNA synthesis
    • Fluoroquinolones
    • Daptomycin
  46. Inhibition of Protein Synthesis
    • aminoglycoside
    • linezolid
    • clindamycin
    • tetracycline and glycylcycline
    • mupirocin
    • retapamulin
  47. Inhibition of Folic Acid Biosynthesis
    • Sulfonamides
    • Trimethoprim
Card Set
Skin Infections
Skin Infections