Is There a Wound Recontamination by Eluates with High Bacterial Load in Negative-Pressure Wound Therapy with Instillation and Dwell Time?

This study investigated bacterial colonization of the foam eluate after negative-pressure wound therapy (NPWT) with instillation and dwell time (NPWTi-d) to obtain an indication of possible recontamination of the wound during NPWTi-d. To detect bacterial colonization and the extent of planktonic and nonplanktonic bioburden as comprehensively as possible, routine culture and molecular biology methods were used. METHODS: Before (time point 1) and after (median 3.0 days; time point 2) NPWT (n = 15) and NPWTi-d with antiseptic installation (n = 15), wound bed [22 acute, eight chronic wounds; median age, 51 years (range, 24 to 91); 26 men], foam, and eluate were examined by routine culture methods and fluorescence in situ hybridization (FISH), polymerase chain reaction, and FISH sequencing (FISHseq). RESULTS: At time point 2, 94.9% (37 of 39) of the pathogens identifiable in the eluate were also detected in the wound bed. Foam and eluate were always bacterially contaminated. NPWTi-d resulted in a significant reduction in the number of pathogen species compared with NPWT (NPWTi-d, time point 1 versus time point 2: P = 0.026; NPWT, time point 1 versus time point 2: not significant). Routine culture of wound bed samples at time point 2 identified only 28 of 52 (53.8%) of the pathogens, whereas examination of wound bed, foam, and eluate and additional FISHseq use detected 50 of 52 (96.2%) of the bacterial species. FISHseq identified biofilm in one and microcolonies in 10 wounds (time point 2). CONCLUSIONS: The bacterial load of the foam is flushed back into the wound during NPWTi-d. FISHseq should be used in addition to the routine culture method when pathogen identification and detection of nonplanktonic bacterial growth is particularly important for the patient’s therapy. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, V.