Infection Detection

Posted: 11 24, 2015

Written and Illustrated by Christina Marvin

Doctoral Candidate in Chemistry at UNC

Demonstration of an “intelligent” wound dressing designed by the Jenkins research group. (1)

Open-wound injuries such as burns are serious enough to warrant hospitalization by themselves but patients often run into further problems when routine treatment is unexpectedly interrupted by bacterial infections. Infections are notorious for increasing the risk of severe complications and prolonging recovery times. Unfortunately, by the time wounds can be positively identified as infected through visual examination, the infection has already progressed into mature or late stages. Surprisingly, technology for early wound infection has been developed only for fundamental laboratory research and currently lacks clinical translation.

Wound dressing has not changed much over the years. In most cases, standard procedures effectively prevent excess bleeding while providing a clean environment for wounds to heal. However, even in the cleanest of surroundings, bacterial infection can be unavoidable. Any tissue abrasion, even a papercut, invites low-level bacterial colonization from the surrounding skin and the external environment. Initially, this background does not pose a significant risk to the individual. However, if the bacteria population continues to grow, it can quickly overwhelm the host immune system and invade tissue, leading to clinical infection and requiring immediate medical attention. If “intelligent” wound dressings could provide early detection, clinicians would be able to start treatment before advanced infection occurs, reducing the risk of serious complications and improving patient outlook for recovery. But how is an “intelligent” wound dressing designed and how would it work?

It would be highly advantageous for both patients and doctors if open-wound infections could be accurately  diagnosed in the early stages, as soon as critical colonization occurs (the bacteria density at which clinical intervention is necessary). To detect early stage infections, Dr. A. Tobias A. Jenkins and his research group at the University of Bath in the United Kingdom1 have developed a prototype of an “intelligent” wound dressing to serve as an early warning system through a simple fluorescent readout that responds to bacterial biofilm formation.

Figure 2 from a 2015 research paper published by Jenkins et al showing a prototype “intelligent” wound dressing. They demonstrate its utility by selectively turning on fluorescence upon lysing vesicles containing a self-quenching dye.

Figure 2 From Jenkins et al (2015)

The material in “intelligent” wound dressings is a mixture of agarose and synthetic lipid vesicles that contain a self-quenching fluorescent dye. When present at high concentrations inside the vesicles, the dye is quenched and does not fluoresce. The lipid vesicles holding the dye are sensitive to cytotoxic virulence factors produced by major wound pathogens. When virulence factors from bacteria in an infected wound reach clinically relevant levels, the vesicles are lysed and the dye is dispersed. Once released, the dye is no longer at a high enough concentration to self-quench, and a fluorescence color change becomes visible. This color change can be detected through vision alone and thus is a simple yet powerful indication of clinical colonization and the need for immediate treatment. At left, the detergent Triton is used to fully lyse the vesicles, and the activated dye is visible under UV light.

The virulence factors that interact with the wound dressing occur in bacterial biofilms. Biofilms, the slimy matrices composed of extracellular DNA, proteins and sugars that bacteria form on surfaces are a common result of open wound infections. Dr. Jenkins’ group tested the prototype dressing in a model of an infected wound bed, using agar matrices with chopped meat-based nutrients, blood plasma, and erythrocytes. Biofilm models were produced on polycarbonate membranes laid on the agarose nutrient mix. Bacterial species selected to “infect” the model wound bed were chosen to represent the species that account for over 80% of colonized wounds: Staphylococcus aureus, Pseudomonas aeruginosa, and Enterococcus faecalis, together referred to as SPE.

Although quantitative differences in fluorescence were observed due to specific characteristics of the various biofilms, the “intelligent” wound dressings applied to each of these SPE models turned fluorescent green under UV light after 5 hours of incubation, successfully detecting the presence of infection. No fluorescence could be observed when the dressings were incubated in the absence of biofilms or with nonpathogenic E. coli, indicating that these wound dressings can selectively detect infection by clinically relevant wound pathogens. To evaluate the wound dressing in a more realistic model, the Jenkins group developed a burn wound biofilm with thermally damaged dermal tissues of porcine (pig) skin. In the laboratory, second degree burns were created on excised skin tissue to form blisters and these sites were inoculated with SPE bacteria to create biofilms. Once again, the “intelligent” wound dressings responded specifically to SPE biofilms, but not to sites without SPE. In most instances, the response was even stronger in this ex vivo model than the biofilm models grown on agar.

Germ FigureClinical infections are a serious and often too common result of wound injuries. This intelligent wound dressing represents an excellent example of the ongoing effort to bring the clinic to the bedside and accurate diagnostics to the patient. The Jenkins group has demonstrated the feasibility of “intelligent” wound dressings that result in an easy-to-read response that is accurate and selective in the early stages of bacterial clinical colonization. This technology has the potential to promote early infection detection that can improve diagnostics, allow for early treatments and ultimately reduce patient risk and recovery time. The Jenkins group is currently working on safety and manufacturing and plans to start clinical trials of their intelligent wound dressing in about 3 years.2

 

Peer edited by Christine Lee & Lindsay Walton

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This article was co-published on the SWAC Blog, The Pipettepen.

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