Bernd Liesenfeld

A study on the ability of quaternary ammonium groups attached to a polyurethane foam wound dressing to inhibit bacterial attachment and biofilm formation.

Bacterial infection of acute and chronic wounds impedes wound healing significantly. Part of this impediment is the ability of bacterial pathogens to grow in wound dressings. In this study, we examined the effectiveness of a polyurethane (PU) foam wound dressings coated with poly diallyl‐dimethylammonium chloride (pDADMAC‐PU) to inhibit the growth and biofilm development by three main wound pathogens, Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter baumannii, within the wound dressing. pDADMAC‐PU inhibited the growth of all three pathogens. Time‐kill curves were conducted both with and without serum to determine the killing kinetic of pDADMAC‐PU. pDADMAC‐PU killed S. aureus, A. baumannii, and P. aeruginosa. The effect of pDADMAC‐PU on biofilm development was analyzed quantitatively and qualitatively. Quantitative analysis, colony‐forming unit assay, revealed that pDADMAC‐PU dressing produced more than eight log reduction in biofilm formation by each pathogen. Visualization of the biofilms by either confocal laser scanning microscopy or scanning electron microscopy confirmed these findings. In addition, it was found that the pDADMAC‐PU‐treated foam totally inhibited migration of bacteria through the foam for all three bacterial strains. These results suggest that pDADMAC‐PU is an effective wound dressing that inhibits the growth of wound pathogens both within the wound and in the wound dressing.

The ability of quaternary ammonium groups attached to a urethane bandage to inhibit bacterial attachment and biofilm formation in a mouse wound model

For proper wound healing, control of bacteria or bacterial infections is of major importance. While caring for a wound, dressing material plays a key role as bacteria can live in the bandage and keep re‐infecting the wound. They do this by forming biofilms in the bandage, which slough off planktonic bacteria and overwhelm the host defense. It is thus necessary to develop a wound dressing that will inhibit bacterial growth. This study examines the effectiveness of a polyurethane foam wound dressing bound with polydiallyl‐dimethylammonium chloride (pDADMAC) to inhibit the growth of bacteria in a wound on the back of a mouse. This technology does not allow pDADMAC to leach away from the dressing into the wound, thereby preventing cytotoxic effects. Staphylococcus aureus, Pseudomonas aeruginosa and Acinetobacter baumannii were chosen for the study to infect the wounds. S. aureus and P. aeruginosa are important pathogens in wound infections, while A. baumannii was selected because of its ability to acquire or upregulate antibiotic drug resistance determinants. In addition, two different isolates of methicillin‐resistant S. aureus (MRSA) were tested. All the bacteria were measured in the wound dressing and in the wound tissue under the dressing. Using colony‐forming unit (CFU) assays, over six logs of inhibition (100%) were found for all the bacterial strains using pDADMAC‐treated wound dressing when compared with control‐untreated dressing. The CFU assay results obtained with the tissues were significant as there were 4–5 logs of reduction (100%) of the test organism in the tissue of the pDADMAC‐covered wound versus that of the control dressing‐covered wound. As the pDADMAC cannot leave the dressing (like other antimicrobials), this would imply that the dressing acts as a reservoir for free bacteria from a biofilm and plays a significant role in the development of a wound infection.

Microfabrication of Biosensors for Neurotransmitter Analysis

We have developed ultrasensitive biosensors for the analysis of neurotransmitters such as glutamate, GABA and lactate. These sensors have micrometer to submicrometer sizes. They are based on biomolecule immobilization on optical fiber probe surfaces. The miniaturized fiber probes are fabricated by either pulling or etching conventional optical fibers. For example, surface immobilized glutamate dehydrogenase (GDH) is being used for glutamate analysis. GDH has been directly immobilized onto an optical fiber probe surface through a new optical fiber sensor fabrication technique using covalent binding mechanisms. None of the direct or indirect physical confinement methods, such as mechanical confinement, gel trapping or membrane immobilization, has been used for the sensor preparation. An optical fiber surface is initially activated by silanization, which adds amine groups (-NH2) to the surface. We then affix functional groups -CHO to the optical fiber surface by employing a bifunctional cross-linking agent, glutaraldehyde. The amino acids of GDH enzyme molecules (or other biomolecules) readily attach to these free -CHO groups on the fiber surface. The sensor is able to detect its substrate, glutamate, by monitoring the fluorescence of reduced nicotinamide adenine dinucleotide (NADH), a product of the reaction between nicotinamide adenine dinucleotide (NAD+) and glutamate. Similar procedures and principle have been used for the development of lactate and GABA sensors. Our biomolecule based biosensors have been applied to the study of single living cell neurophysiological responses.