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Microbiologic Diagnosis of Diabetic Foot Infections

Microbiologic Diagnosis of Diabetic Foot Infections. Albert T. Sheldon, Jr. Ph.D. Microbiology Team Leader Division of Anti-infective Drug Products. Guidance for Industry- Foot Infections in Patients with Diabetic mellitus. Microbiological Considerations

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Microbiologic Diagnosis of Diabetic Foot Infections

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  1. Microbiologic Diagnosis of Diabetic Foot Infections Albert T. Sheldon, Jr. Ph.D. Microbiology Team Leader Division of Anti-infective Drug Products

  2. Guidance for Industry- Foot Infections in Patients with Diabetic mellitus • Microbiological Considerations • All patients should have pre-therapy cultures. • Gram stain and cultures should be obtained from acceptable sources using acceptable methods. • We prefer cultures obtained by leading edge needle aspiration, soft tissue and joint aspiration, bone biopsy and/or surgical debridement. • Microorganisms isolated should be assessed as true pathogens, colonizers, or contaminants. • Only microorganisms designated as true pathogens should be considered in determining microbiological evaluability of enrolled subject. Albert T. Sheldon, Jr. Ph.D. DAIDP

  3. Factors that Influence Infection Rates • Risk of Wound Infection varies according to the following equation:* Dose of bacterial contamination x Virulence Resistance of the Host *Altemeire, W.A., & W.R. Culbertson (1965) Surgical Infection In Moyer, C. et .al. (eds.): Surgery, Principles and Practices, 3rd ed. Philadelphia, Lippincott Co. Albert T. Sheldon, Jr. Ph.D. DAIDP

  4. Host Factors that Influence Infection Rates • Diversity and abundance of microorganisms present in the wound are also influenced by host factors: • Wound type, depth, location, and quality • Presence of nonviable exogenous contamination • Peripheral blood insufficiency • Immune competence of the host Albert T. Sheldon, Jr. Ph.D. DAIDP

  5. Manual of Clinical Microbiology* “The use of specimens for bacteriological analysis requires that specific clinical material be collected, stabilized, and transported according to exacting specifications to insure valid results.” *Murray, P. R., E. J. Baron, J. H. Jorgensen, M. A. Pfaller, and R. H. Yolken. 2003. Manual of Clinical Microbiology, 8th Edition. ASM Press, Washington D.C. Albert T. Sheldon, Jr. Ph.D. DAIDP

  6. Clinical Microbiology • Implicit in this definition are two issues that are of interest to the discussion of decubitus foot infections. • The methods used to collect the clinical sample and • the validity of the results to assess the involvement of an organism in the etiology of the disease. Albert T. Sheldon, Jr. Ph.D. DAIDP

  7. 1. Methods used in Collection of Microbiological Wound Samples • Deep Tissue Techniques • Biopsy and/or surgically debrided tissue*+ • Leading edge Needle aspirate*+ • Joint fluid or synovium+ • Bone specimen+ • Blood+ • Surface Sampling Techniques • Swab* • Curettage* • Dermabrasion • Velvet pad surface imprint *Published methods used in decubitus ulcer sampling. + Method recommended in Agency guidance document are deep tissue techniques. Albert T. Sheldon, Jr. Ph.D. DAIDP

  8. Comparison of Sampling MethodsSapico F.L., et. Al. (1984) Rev Infect Dis. 6:S171-S176 Albert T. Sheldon, Jr. Ph.D. DAIDP

  9. Comparison of Sampling MethodsSapico F.L., et. Al. (1984) Rev Infect Dis. 6:S171-S176 Albert T. Sheldon, Jr. Ph.D. DAIDP

  10. Relationship Between Biopsy & Swab: Burn Wounds Thomson, P.D., (1994) Amer J Surgery 167:7S-10S Albert T. Sheldon, Jr. Ph.D. DAIDP

  11. Relationship Between Quantitative Culture & Swab Breidenbach W,C., & S. Trager (1994) Plats. Reconstr. Surg. 95:860-865 • Study purpose: • To determine the relationship between the quantity of bacteria and infection in complex extremity wounds, and • To compare the predictive value for wound infection of quantitative cultures versus other factors considered to have predictive value for wound infection. I will focus on the latter purpose of the study. Albert T. Sheldon, Jr. Ph.D. DAIDP

  12. Relationship Between Quantitative Culture & Swab (cont) Breidenbach W,C., & S. Trager (1994) Plats. Reconstr. Surg. 95:860-865 • Evaluated 50 patients with complex wounds-defined as a soft-tissue defect that required flap for closure. • Quantitative cultures (biopsy) compared to • Clinical parameters (factors considered to have predictive value in wound infection; wound position, mechanism of injury, fracture type) • Laboratory test (Swab culture) • 28 patients had quantitative cultures obtained after debridement and high pressure wash prior to flap closure. 16 patients had swab cultures. 2-5 samples obtained per wound. Albert T. Sheldon, Jr. Ph.D. DAIDP

  13. Criteria for Positive/Negative Test, Infection, and PrevalenceBreidenbach W,C., & S. Trager (1994) Plats. Reconstr. Surg. 95:860-865 Albert T. Sheldon, Jr. Ph.D. DAIDP

  14. Criteria for Positive/Negative Test, Infection, and PrevalenceBreidenbach W,C., & S. Trager (1994) Plats. Reconstr. Surg. 95:860-865 Albert T. Sheldon, Jr. Ph.D. DAIDP

  15. Predictive values, Sensitivity, & Specificity of Tests Studied Albert T. Sheldon, Jr. Ph.D. DAIDP

  16. Predictive values, Sensitivity, & Specificity of Tests Studied Albert T. Sheldon, Jr. Ph.D. DAIDP

  17. 2. Interpretation of Microbiologic Diabetic foot infection Samples (or Qualitative Microbiology) • Diabetic foot ulcers are polymicrobic.* • S. aureus is the predominant aerobic species followed by S. epidermidis, Streptococcus spp., P. aeruginosa, Enterococcus spp., and coliform bacteria. • The predominant anaerobic species are Peptostreptococcus spp., Bacteroides spp., and Prevotella spp. • Application of good microbiological techniques will allow isolation of anaerobes from up to 95% of decubitus ulcers. However, such studies are not usually performed due to the labor intensive nature of anaerobic microbiological studies. *Bowler, P.G., et. al. (2001) Clin Microbiol Rev 14:244-269. Albert T. Sheldon, Jr. Ph.D. DAIDP

  18. Schools of Thought* • Although microorganisms are responsible for wound infections, there is controversy regarding their role. Published literature is inconclusive! • The density of microorganisms is the critical factor in determining whether a wound is likely to heal. • The presence of specific pathogens is of primary importance in delayed healing. • Microorganisms are of minimal importance in delayed healing. • Debate whether a wound should be sampled, the value of the results and the method that should be used. Albert T. Sheldon, Jr. Ph.D. DAIDP

  19. Conclusions • Widespread controversy still exists • Regarding the exact mechanisms by which microorganisms cause wound infection, • Regarding the significance of microorganisms in nonhealing wounds that do not exhibit signs of clinical infection, and • Regarding the best microbiological techniques to monitor the microbiology of wounds. • ASM Manual Clinical Microbiology states “A swab is not the specimen of choice…Since a swab specimen of a decubitus ulcer provides no clinical information.” Albert T. Sheldon, Jr. Ph.D. DAIDP

  20. Conclusions • A regulatory agency must require microbiological methods that provide us with confidence and data necessary to assess the response of antimicrobials for their intended uses. • We describe, in our guidance document, what we consider to be relevant methods. These are the deep tissue techniques discussed in a previous slide. Albert T. Sheldon, Jr. Ph.D. DAIDP

  21. Louis Pasteur “ The germ is nothing. It is the terrain in which it is found that is everything.” Pasteur, L. (1880) De l’attenuation virus du cholera des poules. CR Acad. Sci. 91: 673-680. Albert T. Sheldon, Jr. Ph.D. DAIDP

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