ANTIBIOTIC‐RESISTANT GRAM‐NEGATIVE BACTERIA IN DEEP TISSUE CULTURES

Abstract

Past studies have demonstrated that antibiotic-resistant gram-negative organisms (AR GNO) colonize the surface of chronic wounds. (1–4) We performed a chart review to determine the prevalence of antibiotic-resistant gram-negative organisms in deep tissue of non-healing and infected wounds after sharp debridement has been performed. We reviewed records of bacterial wound cultures for all patients seen over a six-month period at an urban wound healing program. For each patient, all cultures that had been obtained at our institution were reviewed. Cultures were included in analysis if they were derived from deep tissue obtained after sharp excisional debridement of all grossly necrotic and non-viable tissue. Clinical indications for wound debridement included infection, or failure to heal in a non-ischemic wound. Antibiotic resistance was defined as resistance to carbapenems in acinetobacter strains (5); resistance to third-generation cephalosporins in klebsiella strains; and resistance to fluoroquinolones, third-generation cephalosporins, or carbapenems in pseudomonas strains. (6) Intermediate sensitivity was considered to be resistance. Diphtheroids and coagulase-negative staphylococcus were not included in assessment of polymicrobial infection. Thirty of 336 total patients (8.9%, 95%CI 8.7–9.2%) had deep tissue cultures with antibiotic-resistant acinetobacter, pseudomonas, and/or klebsiella. Four patients had more than one of these organisms. There were 7 patients with resistant acinetobacter, 8 with klebsiella, and 19 with pseudomonas Of the 19 patients with antibiotic resistant pseudomonas, 12 had resistance to fluoroquinolones, 5 to carbapenems, and 15 to third-generation cephalosporins. Eleven patients had resistance to more than one of these classes, and two patients had resistance to all three classes. Of the patients with carbapenem-resistant acinetobacter, all isolates were resistant to cephalosporins and fluoroquinolones. No resistance to polymixin was observed. Of the 30 patients, 12 had venous stasis ulcers; 7 ischemic wounds; 5 pressure ulcers; 5 diabetic foot ulcers; and 1 pyoderma. Twenty-five cultures were obtained in the operating room, and five in the outpatient or bedside setting. Of 10 patients with resistant Gram-negative organisms in bone cultures, 9 had pathology specimens, of which 5 showed histopathology consistent with osteomyelitis. Twenty-two cultures (65%) were polymicrobial infections. Of the 30 patients with positive cultures, 50% were 65 years or older, 30% lived in a nursing home, and 23% were bedbound. There was a high rate of chronic disease: 63% of patients were diabetic, and 9% were immunosuppressed from HIV, post-transplant medications, or chemotherapy. Patients had been hospitalized on the wound program’s inpatient unit an average of 3.5 times over the previous three years. This study documents the presence of antibiotic-resistant Gram-negative organisms in deep tissue after wound debridement. Antibiotic regimens for resistant bacteria often require intravenous administration and have higher rates of adverse effects. We hypothesize that wound debridement decreases the risk of developing resistant organisms by surgically removing infected tissue. We further hypothesize that, in the presence of resistant organisms, tailored antibiotic regimens lead to faster resolution of infection and increase healing rates.