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

Abstract

Background: 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.

Fig. 1.

Consistency of detection of identified bacterial species in wound bed, foam, and eluate before and after NPWT or NPWTi-d application in all 30 patients. The numbers given in the circles, separated according to form of therapy, indicate the frequency of the detection of the respective species. A total of 39 different bacterial species were identified at the two time points (time points 1 and 2) and in all sample materials (wound bed, foam, eluate). Gray circle: NPWT; green circle: NPWTi-d.

Fig. 2.

Number of bacterial species as detected by all diagnostic methods in both groups (NPWT and NPWTi-d). Shown is the number in different samples [wound bed at time point 1 (WB1), wound bed at time point 2 (WB2), foam, and eluate]. Created with BioRender.com.

Fig. 3.

Number of bacterial species identified in each individual patient in the wound bed (time points 1 and 2), foam, and eluate at time point 2 in the NPWT group (n = 15 patients) and NPWTi-d group (n = 15 patients). Created with GraphPad Prism 9.

Fig. 4.

Fluorescence in situ hybridization of wound tissue in a patient before NPWT. Culture was positive for Streptococcus sp. and Enterobacteriaceae. (Left) Overview shows the tissue in green and host cell nuclei in blue. Inset marks a region where bacteria detected by the panbacterial FISH probe are visible within a small biofilm. At higher magnification (above, right), the Streptococcus genus-specific FISH probe (orange) shows a strong fluorescence signal, indicating active bacteria. In DAPI (below, right), additional rods are visible, in line with Enterobacteriaceae detected by culture.

Fig. 5.

Fluorescence in situ hybridization of a NPWT foam that was culture-positive for Pseudomonas aeruginosa and Staphylococcus aureus. The section was hybridized with the Staphylococcus genus–specific probe STAPHY_CY3 and the Pseudomonas genus-specific probe PSMG_FITC. DAPI was used for visualization of nucleic acids in host cell nuclei and bacteria. (Above) Overview shows negative pressure wound therapy foam colonized with host cell nuclei and bacterial biofilms. Inset marks a region were FISH-positive bacteria are visible within biofilms. At higher magnification (below), the Staphylococcus genus–specific FISH probe (first round inset, orange) and the Pseudomonas genus–specific FISH (second round inset, green) shows a strong fluorescence signal, indicating active bacteria of both species.