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Rensselaer Polytechnic Institute develops a new method to kill pathogenic bacteria
Biomimicing nano-particles may provide with a new effective food preservation technique

Engineers and researchers at Rensselaer Polytechnic Institute have been working to develop a new method to kill deadly pathogenic bacteria, including listeria, for a range of uses, dominantly the food industry. This industrial innovation presents an alternative to the use of antibiotics or chemical decontamination in food supply systems.

Using inspiration derived from Nature, the researchers successfully adhered a cell lytic enzyme to food-safe silica nanoparticles, thus creating a coating with the demonstrated ability to selectively kill listeria-dangerous foodborne bacteria that causes an estimated 500 deaths every year in the United States. The coating kills the bacteria upon contact, even at very high concentrations, within a short time span without affecting other bacteria or organisms. The lytic enzymes can also, using this method, be attached to starch nanoparticles that are commonly used in food packaging.

Listeria is a bacterial genus containing seven species. Named after the English pioneer of sterile surgery, Joseph Lister, Listeria species are Gram-positive bacilli and are typified by ''L. monocytogenes'', and they are the the causative agents of listeriosis. This infection occurs primarily in newborn infants, elderly patients, and patients who are immune-compromised.

This new method is very flexible, and by using different lytic enzymes, could be modified to create surfaces that selectively target other deadly bacteria such as anthrax, bacillus or cocii, said Jonathan Dordick, vice president for research at Rensselaer, who helped lead the study.

This research took place in the Rensselaer Center for Biotechnology and Interdisciplinary Studies and the Rensselaer Nanoscale Science and Engineering Center for the Directed Assembly of Nanostructures, and combined the efforts and skills of chemical engineers, biotechnologists and material scientists. Collaborating with Dordick were Ravi Kane, Professor of Chemical and Biological Engineering, and Linda Schadler, associate dean for academic affairs for the Rensselaer School of Engineering.

"In this study, we have identified a new strategy for selectively killing specific types of bacteria. Stable enzyme-based coatings or sprays could be used in food supply infrastructure-from picking equipment to packaging to preparation-to kill listeria before anyone has a chance to get sick from it," said Kane. "What's most exciting is that we can adapt this technology for all different kinds of harmful or deadly bacteria."

This recent study by the same team builds upon their success in 2010 of creating a coating for killing methicillin resistant Staphylococcus aureus (MRSA), the primal culprit responsible for antibiotic resistant infections. While this coating was intended for use on surgical equipment and hospital walls, the development of a listeria-killing coating had to be food-safe, which presented additional challenge.

The team found inspiration in nature; the lytic enzymes used by viruses. Phages are viruses that infect bacterial cells, and once they have inserted their DNA and reproduced, the new viroids must escape the cells to be able to spread the infection. At that point the original phage releases a cue that activates the inserted gene that synthesizes lytic enzymes, which break down the bacterial wall from within, releasing the new generation of viruses. The team used this principle to break the walls from outside.

The next task was to stabilize the listeria-killing lytic enzymes, called Ply500, so they attached them to U.S. Food and Drug Administration-approved silica nanoparticles to create an ultra-thin film. The researchers used maltose as a binding protein to attach Ply500 to conventional, edible starch nanoparticles commonly used in food packaging. Both formulations showed as effective. Within 24 hours all listeria at concentrations as high as 100,000 bacteria per milliliter were killed. This concentrations are significantly higher than normally found in food contamination situations.

Results of the study are detailed in the paper "Enzyme-based Listericidal Nanocomposites," published April 3. in the journal Scientific Reports from the Nature Publishing Group.
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