Dr. Nancy Cornish Director of Microbiology Methodist and Children’s Hospitals CUTANEOUS INFECTIONS

Sinus Tracts LAB DX: –Surgical exploration to obtain deep tissue biopsies for cultures is BEST –Poor correlation between results of culturing drainage/opening of fistula/sinus tract and cultures obtained from deeper infected tissues as surface specimens become colonized with bacteria/fungus –Obtain blood cultures if systemic symptoms present fever, chills –Granules (if present) should be collected crushed and cultured in cases of mycetoma

Burn Wounds Quantitative culture definition: –Burn wound complications associated with > 10 5 organisms (CFU)/gram of tissue Controversial –Surface cultures misleading due to colonization –Deep tissue biopsies, marked variation of number of bacteria within tissue –Inability to estimate the depth to which organisms have spread

Simple Postoperative Wound Infections Wound is contaminated with bacteria –Patient’s own flora –Caregiver’s flora –Hospital environment flora

Predisposing Host Risk Factors –Obesity –Diabetes –Vascular insufficiency –Immune suppression

Microbial Risk Factors –Microbial load (how many?) –Virulence factors carried by bacteria S. aureus Group A strep Ps. aeruginosa

Surgical Risk Factors –Duration of an operation –Poor hemostasis –Presence of foreign bodies Sutures Mesh Grafts

Simple Postoperative Wound Infections In the presence of risk factors, the inoculums size necessary to initiate infection is much smaller than that required to cause infection in healthy tissues.

Simple Postoperative Wound Infections LAB DX Important: –Best specimen aspirate of pus (at least 1 cc) –Gram stain –Plant blood, MacConkey agar at 37°C TX: –Broad spectrum empiric therapy started based on gram stain results if possible –Antimicrobial therapy tailored to culture results when available

Complicated Wound Infections Affects skin and subjacent structures Follow surgery or trauma Severe, rapidly progressive high mortality rate Anaerobes involved, esp. Clostridium spp.

Complicated Wound Infections 3 Syndromes –Crepitant cellulitis Clostridial Non-clostridial –Necrotizing fasciitis Meleney’s gangrene (abdominal surgery) Fournier’s disease (perineum and scrotum) –Gas gangrene with Myonecrosis Associated with Clostridium perfringens

Complicated Wound Infections LAB DX –Tissue and fluid cultures from surgery set up for aerobic and anaerobic work up and gram stain (5 ml or grams of tissue) Gram stain often shows lack of white cells and presence of bacteria and cellular debris –Blood cultures TX –Surgical debridement ASAP! –Broad-spectrum antimicrobial therapy is indicated to cover gram positive and gram negative organisms as well as anaerobes

Infections Complicating Bite Wounds Oral flora of biter is injected into the bite –Human bites Severe necrotizing infections Aggressive treatment –Debridement –Antibiotics –Animal Deep puncture wounds Unusual organisms –Pasteurella multocida (dogs/cats) –Streptobacillus moniliformis (rats) –Cat scratch disease (Bartonella henselae)

Bite Wounds LAB DX: –Culture of fresh bite wound is unrewarding - reveals only the oral flora of the biter –Culture, if needed, is best if aspirated pus taken from depths of wound taken after infection develops TX: –Should cover both aerobic and anaerobic organisms = Amoxicillin/Clavulanic acid

For copies of specimen collection posters go to:

Thank You Any questions?