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The Microbiology of Wounds Neal R. Chamberlain, Ph.D., Department of Microbiology/Immunology KCOM.

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Presentation on theme: "The Microbiology of Wounds Neal R. Chamberlain, Ph.D., Department of Microbiology/Immunology KCOM."— Presentation transcript:

1 The Microbiology of Wounds Neal R. Chamberlain, Ph.D., Department of Microbiology/Immunology KCOM

2 Microbes and Chronic Wounds zAll chronic wounds are contaminated by bacteria. zWound healing occurs in the presence of bacteria. zCertain bacteria appear to aid wound healing. zIt is not the presence of organisms but their interaction with the patient that determines their influence on wound healing.

3 Definitions zWound contamination: the presence of non-replicating organisms in the wound. zAll chronic wounds are contaminated. zThese contaminants come from the indigenous microflora and/or the environment. zMost contaminating organisms are not able to multiply in a wound. (Ex. Most organisms in the soil won’t grow in a wound).

4 Definitions zWound colonization: the presence of replicating microorganisms adherent to the wound in the absence of injury to the host. zThis is also very common. zMost of these organisms are normal skin flora. zStaphylococcus epidermidis, other coagulase negative Staph., Corynebacterium sp., Brevibacterium sp., Proprionibacterium acnes, Pityrosporum sp..

5 Definitions zWound Infection: the presence of replicating microorganisms within a wound that cause host injury. zPrimarily pathogens are of concern here. zExamples include; Staphylococcus aureus, Beta- hemolytic Streptococcus (S. pyogenes, S. agalactiae), E. coli, Proteus, Klebsiella, anaerobes, Pseudomonas, Acinetobacter, Stenotrophomonas (Xanthomonas).

6 Microbiology of Wounds zThe microbial flora in wounds appear to change over time. zEarly acute wound; Normal skin flora predominate. zS. aureus, and Beta-hemolytic Streptococcus soon follow. (Group B Streptococcus and S. aureus are common organisms found in diabetic foot ulcers)

7 Microbiology of Wounds zAfter about 4 weeks yFacultative anaerobic gram negative rods will colonize the wound. yMost common ones= Proteus, E. coli, and Klebsiella. zAs the wound deteriorates deeper structures are affected. Anaerobes become more common. Oftentimes infections are polymicrobial (4-5).

8 Microbiology of Wounds zLong-term chronic wounds oftentimes contain more anaerobes than aerobes. zAerobic gram-negative rods also infect wounds late in the course of chronic wound degeneration. Usually acquired from exogenous sources; bath and foot water zEx. Pseudomonas, Acinetobacter, Stenotrophomonas (Xanthomonas).

9 Microbiology of Wounds zOrganisms like Pseudomonas are not very invasive unless the patient is highly compromised (ex. Ecthyma gangrenosum in neutropenic patients). zThese organisms are associated with marked wound deterioration due to endotoxin, enzymes, and exotoxins.

10 Microbiology of Wounds zAs the wounds go deeper and become more complex they can infect the underlying muscles and bone causing osteomyelitis. zColiforms and anaerobes are associated with osteomyelitis in these patients. You also see Staphylococcus aureus.

11 Microbiology of Wounds zEnterococcus and Candida are often isolated from wounds. zTreating a patient for these organisms is only indicated if there are no other pathogens present and the organisms are present in high concentrations (10 6 CFU’s per gram of tissue)

12 Microbiology of Wounds zIn summary: early chronic wounds contain mostly gram-positive organisms. zWounds of several months duration with deep structure involvement will have on average 4-5 microbial pathogens, including anaerobes (see more gram- negative organisms).

13 From Colonization to Infection? zMany factors affect the progress of microorganisms in a wound from colonization to infection: zInfection= dose X virulence __________host resistance zThe number of organisms. zThe virulence factors they produce. zThe resistance of the host to infection.

14 Dose of Bacteria zDiffers depending on the organism involved. zSome organisms would need to be in high concentrations. (ex. Candida, Enterococcus) zVarious combinations of bacterial species result in more host damage (synergy) zExample; Group B Streptococcus (S. agalatiae) and Staphylococcus aureus.

15 Dose of Bacteria zOrganisms that should be treated regardless of the numbers present. zBeta-hemolytic streptococci, Mycobacteria sp., Bacillus anthracis, Yersinia pestis, Corynebacterium diphtheriae, Erysipelothrix rhusiopathiae, Leptospira sp., Treponema sp., Brucella sp., Clostridium sp., VZV, HSV, dimorphic fungi, Leishmaniasis.

16 Bacterial Problems to Consider zStreptococcus pyogenes zCan result in necrotizing fasciitis or streptococcal toxic shock syndrome. Not very common. Only about 520 cases per year of each condition. zMore common to see cellulitis and erysipelas after infection of a chronic wound.

17 Bacterial Problems to Consider zClostridium tetani zContamination of chronic wounds by exogenous sources is common. zOf the 41 cases of tetanus that occurred in 1998, a total of 16 (39%) were among persons aged greater than or equal to 60 years. zMake sure your patients have gotten their tetanus vaccination.

18 Bacterial Problems to Consider zErysipelothrix rhusiopathiae can infect chronic wounds. Associated with hog farmers and people who fish. zMycobacteria marinum and M. ulcerans can infect chronic wounds. Think of people who have aquariums, pools, go fishing, etc..

19 Virulence zFactors an organism produces can result in host damage. zEx. Hyaluronidase (Streptococcus pyogenes), proteases (Staphylococcus aureus, Pseudomonas aeruginosa), toxins (Streptococcus pyogenes, Staphylococcus aureus), endotoxin (gram negative organisms).

20 Virulence zSome organisms produce few virulence factors. zHowever, synergy between different bacterial factors can cause host damage. zGroup B Streptococcus and Staphylococcus aureus: Synergy between two toxins results in hemolysis.

21 Host Resistance zHost resistance is the single most important determinant in wound infection. zLocal and Systemic factors both play a role in increasing the chances a wound will become infected.

22 Host Resistance zLocal factors that increase chances of wound infection: yLarge wound area yIncreased wound depth yDegree of chronicity yAnatomic location (distal extremity, perineal) yForeign body yNecrotic tissue yMechanism of injury (bites, perforated viscus) yReduced perfusion

23 Wound Depth can Result in Different Diseases

24 Host Resistance zSystemic factors that increase chances of wound infection: yVascular disease yEdema yMalnutrition yDiabetes yAlcoholism yPrior surgery or radiation yCorticosteroids yInherited neutrophil defects

25 How do you know when a wound is infected? zThis can be very difficult. zA continuum exists between when pathogens colonize the wound and then start to cause damage. zThere is no absolutely foolproof laboratory test that will aid in this diagnosis.

26 How do you know when a wound is infected? zOne feature is common to all infected chronic wounds; zThe failure of the wound to heal and progressive deterioration of the wound. zUnfortunately, wound infections are not the only reasons for poor wound healing.

27 How do you know when a wound is infected? zThe typical features of wound infections: zincreased exudate zincreased swelling zincreased erythema zincreased pain zincreased local temperature zPeriwound cellulitis, ascending infection, change in appearance of granulation tissue (discoloration, prone to bleed, highly friable).

28 Specimen Collection and Culture Techniques. zThere is a good deal of controversy concerning specimen collection. zThe gold standard collection method is to do a tissue biopsy or needle aspirate of the leading edge of the wound after debridement. z>10 5 CFU/gm of tissue= greater likelihood of sepsis developing.

29 Specimen Collection and Culture Techniques. zIndicate the specific anatomic site the biopsy is collected from. zIndicate whether this is a surface or deep wound. Ask for a smear and gram stain of the tissue. zSurface wounds are NOT cultured for anaerobes. zDeep wounds are cultured for anaerobes.

30 Specimen Collection and Culture Techniques. zIf a tissue biopsy is not possible; zcleanse the wound with sterile saline zvigorously swab the base of the lesion zSurface wounds place the swab in a sterile container for transport. zDeep wounds place the swab in a sterile anaerobic container for transport.

31 Thank You zI would like to thank yKCOM yDepartment of Continuing Medical Education zThe following article is a helpful review of this topic: Dow, G., Browne, A., and Sibbald, R.G. Infection in Chronic Wounds: Controversies in Diagnosis and Treatment. Ostomy/Wound Management. 1999;45(8):23-40.


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