Engineering researchers at Rensselaer Polytechnic Institute
have developed a new method to kill deadly pathogenic bacteria, including
listeria, in food handling and packaging. This innovation represents an
alternative to the use of antibiotics or chemical decontamination in food
How the method was developed
Using nature as their inspiration, the researchers
successfully attached cell lytic enzymes to food-safe silica nanoparticles, and
created a coating with the demonstrated ability to selectively kill listeria—a
dangerous foodborne bacteria that causes an estimated 500 deaths every year in
the United States. The coating kills listeria on contact, even at high
concentrations, within a few minutes without affecting other bacteria. The lytic
enzymes can also be attached to starch nanoparticles commonly used in food
This new method is modular, and by using different lytic
enzymes, could be engineered to create surfaces that selectively target other
deadly bacteria such as anthrax, said Jonathan Dordick, vice president for
research and the Howard P. Isermann Professor at Rensselaer, who helped lead
This research, which combined the expertise of chemical
engineers and material scientists, 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.
Collaborating with Dordick were Rensselaer colleagues Ravi Kane, the P.K.
Lashmet Professor of Chemical and Biological Engineering, and Linda Schadler,
the Russell Sage Professor and 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," Kane said. "What's most exciting is that we can adapt
this technology for all different kinds of harmful or deadly bacteria."
Results of the study are detailed in the paper
"Enzyme-based Listericidal Nanocomposites," published in the journal Scientific Reports from the Nature
Publishing Group. See the paper online here.
How it works
This most recent study builds upon the research team's
success in 2010 of creating a coating for killing methicillin resistant
Staphylococcus aureus(MRSA), the bacteria responsible for antibiotic resistant
infections. While the previous coating was intended for use on surgical
equipment and hospital walls, the development of a listeria-killing coating had
the extra challenge of needing to be food-safe.
Dordick and the research team found their answer in lytic
enzymes. Viruses that affect bacteria, called phages, inject their genetic
material into healthy cells. The phage takes over a healthy cell, and in effect
transforms the host cell into a little factory that creates more phages. Near
the end of its life cycle, the original phage creates and releases lytic
enzymes, which break down and make holes in cell walls of the infected
bacteria. The manufactured phages escape through these holes and go on to
infect other healthy cells.
Nature used lytic enzymes to break out of bacterial cells,
Dordick said, and the researchers worked for years to exploit the same lytic
enzymes to break into bacteria such as MRSA and listeria.
To stabilize the listeria-killing lytic enzymes, called
Ply500, the researchers attached them to U.S. Food and Drug
Administration-approved silica nanoparticles to create an ultra-thin film. The
researchers also used maltose binding protein to attach Ply500 to edible starch
nanoparticles commonly used in food packaging. Both Ply500 formulations were
effective in killing within 24 hours all listeria at concentrations as high as
100,000 bacteria per millilitre—a significantly higher concentration than
normally found in food contamination situations.
"Starch is an inexpensive, edible material often
sprayed into the packaging as a powder layer on meat product. We took advantage
of the natural affinity of a maltose binding protein fused to Ply500, and
biologically bound Ply500 to starch as a non-antibiotic, non-chemical agent for
reducing the threat of listeria to our food supply," Schadler said.
Looking forward, the research team plans to continue
investigating new methods for harnessing the power of lytic enzymes to
selectively kill harmful bacteria.