Diabetic Foot Infection

Paul Auwaerter, M.D.
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PATHOGENS

  • Most diabetic foot infections (DFIs) are polymicrobial; however, if the patient hasn’t recently received abx therapy, often monomicrobial and due to either staphylococcal or streptococcal infection.
  • Frequent pathogens: most DFIs are polymicrobial.
    • Initially, wounds usually with Gram-positive flora from the skin; as it becomes more chronic, tilts toward Gram negatives. Following broad-spectrum abx, flora may evolve to MRSA, VRE and more resistant Gram negatives.
    • Aerobic Gram positive:
      • Staphylococcus aureus
        • Among the most commonly isolated pathogen in N. America and European series.
      • Streptococcal spp.
        • Especially GAS, GBS, group C or G streptococci
      • Enterococcus spp.
      • Coagulase-negative staphylococci usually a contaminant if obtained from a superficial swab, but should be viewed as authentic if obtained from deep tissue or bone.
    • Aerobic Gram negative
      • Enterobacteriaceae 
      • Pseudomonas aeruginosa (although frequently a commensal when found, studies using abx without antipseudomonal activity often yield similar results e.g., ertapenem v. piperacillin/tazobactam[18])
    • Anaerobes, facultative anaerobes: usually when ulcers are deep, chronic and/or necrotic tissue is present.
      • B. fragilis
      • Clostridia spp.
      • Peptococcus and Peptostreptococcus
  • Superficial, early infections (cellulitis, cellulitis involving blisters and shallow ulcers) are typically caused by S. aureus or beta-hemolytic streptococci.
  • Infections of ulcers that are chronic or previously treated with antibiotics may be caused by aerobic Gram-negative bacilli, S. aureus or Streptococci.
  • Deep soft tissue infections, osteomyelitis, and gangrene are more often polymicrobial, including aerobic Gram-negative bacilli and anaerobes (anaerobic streptococci, Bacteroides fragilis group, Clostridium species), but Staphyloccocus aureus is also common as single pathogen.
  • Multi-drug resistant Gram-negative organisms described in DFI especially ESBL, but most resistant organisms w/ reports from India and warmer climates.

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PATHOGENS

  • Most diabetic foot infections (DFIs) are polymicrobial; however, if the patient hasn’t recently received abx therapy, often monomicrobial and due to either staphylococcal or streptococcal infection.
  • Frequent pathogens: most DFIs are polymicrobial.
    • Initially, wounds usually with Gram-positive flora from the skin; as it becomes more chronic, tilts toward Gram negatives. Following broad-spectrum abx, flora may evolve to MRSA, VRE and more resistant Gram negatives.
    • Aerobic Gram positive:
      • Staphylococcus aureus
        • Among the most commonly isolated pathogen in N. America and European series.
      • Streptococcal spp.
        • Especially GAS, GBS, group C or G streptococci
      • Enterococcus spp.
      • Coagulase-negative staphylococci usually a contaminant if obtained from a superficial swab, but should be viewed as authentic if obtained from deep tissue or bone.
    • Aerobic Gram negative
      • Enterobacteriaceae 
      • Pseudomonas aeruginosa (although frequently a commensal when found, studies using abx without antipseudomonal activity often yield similar results e.g., ertapenem v. piperacillin/tazobactam[18])
    • Anaerobes, facultative anaerobes: usually when ulcers are deep, chronic and/or necrotic tissue is present.
      • B. fragilis
      • Clostridia spp.
      • Peptococcus and Peptostreptococcus
  • Superficial, early infections (cellulitis, cellulitis involving blisters and shallow ulcers) are typically caused by S. aureus or beta-hemolytic streptococci.
  • Infections of ulcers that are chronic or previously treated with antibiotics may be caused by aerobic Gram-negative bacilli, S. aureus or Streptococci.
  • Deep soft tissue infections, osteomyelitis, and gangrene are more often polymicrobial, including aerobic Gram-negative bacilli and anaerobes (anaerobic streptococci, Bacteroides fragilis group, Clostridium species), but Staphyloccocus aureus is also common as single pathogen.
  • Multi-drug resistant Gram-negative organisms described in DFI especially ESBL, but most resistant organisms w/ reports from India and warmer climates.

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