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‘Protective coat’ for Listeria discovered

DGC activities of the L. monocytogenes proteins DgcA-C
DGC activities of the L. monocytogenes proteins DgcA-C

A substance that greatly increases the survival of Listeria monocytogenes has been discovered by researchers who hope it will lead to better techniques to combat the pathogen.

Mark Gomelsky, a professor in the University of Wyoming’s Department of Molecular Biology, and other researchers discovered and characterized exopolysaccharide (EPS), that Listeria secretes on its cell surface under certain conditions.

The EPS coats bacterial cells and makes them form aggregates or clumps, which are strongly protected from commonly used disinfectants and desiccation (extreme drying).

EPS as a protective coat

EPS can be envisaged as a protective coat around the cell.

Researchers have debated whether Listeria could produce EPS, which is a sugar polymer, but Gomelsky said their findings prove that it does.

“We think that EPS plays a significant role in survival of Listeria in the environment, during food storage, processing and transportation,” he said.

Volkan Koseoglu, a UW student in in the Molecular and Life Sciences Ph.D. program, used chemical agents, including bleach, hydrogen peroxide and other disinfectants used in the food processing industry to test what role EPS plays in protecting Listeria strains.

Chemicals were effective in killing the bacteria that did not produce the EPS coat, but were much less effective in killing the ones that produced EPS. When bleach was used, cells in the clumps coated by EPS were found to be strongly protected.

Koseoglu said it is possible to readily kill Listeria cells with a disinfectant like bleach, but clumped cells cannot be easily killed.

Listeria cells can be transferred to deli meats when they are sliced on a contaminated food slicer.

Sugar composition of EPS

Currently, the UW researchers are determining the sugar composition of EPS.

“This may provide crucial information as to how to remove EPS from Listeria. We also want to determine what signals make Listeria produce EPS,” said Kurt Miller, a UW professor of molecular biology.

“The long-term strategy is to discover how to stop Listeria from producing EPS and how to make EPS-coated Listeria less resistant to disinfection.”

This work was supported by a postdoctoral fellowship from The China Scholarship Council, and grants from UW’s Agricultural Experimental Station, the National Science Foundation and National Institutes of Health.

Li-Hong Chen, a visiting scientist from Inner Mongolia Agricultural University in China, conducted the bulk of the research, Tuzun Guvener, a former UW post-doctoral fellow; and Joseph Reed, a former UW molecular biology student, also contributed to the paper.

Source: PLoS Pathogens

Online ahead of print DOI: 10.1371/journal.ppat.1004301

Cyclic di-GMP-dependent Signaling Pathways in the Pathogenic Firmicute Listeria monocytogenes

Authors: Li-Hong Chen, Volkan K. Köseoğlu, Zehra T. Güvener, Tanya Myers-Morales, Joseph M. Reed, Sarah E. F. D'Orazio, Kurt W. Miller, Mark Gomelsky

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