Dr. Nancy CornishDirector of Microbiology

Methodist and Children’s Hospitals

CUTANEOUS INFECTIONS

Sinus TractsLAB 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 > 105

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 structuresFollow surgery or traumaSevere, rapidly progressive high mortality rateAnaerobes 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 InfectionsLAB 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:

www.thepathologycenter.org

Thank YouAny questions?

Nancy.Cornish@nmhs.org