May 9, 2022

Microbiologists to study biofilms guarding Listeria
By Jeff Mulhollem, Penn State University

Microbiologists in Penn State’s College of Agricultural Sciences have received a $605,000 grant from the U.S. Department of Agriculture to study how microbial biofilms protect Listeria monocytogenes, the bacterium that causes the deadly foodborne illness listeriosis.

Jasna Kovac, Lester Earl and Veronica Casida Career Development Professor of Food Safety, along with Luke LaBorde, professor of food science, will use the funding from USDA’s National Institute of Food and Agriculture to conduct research on the interactions between microorganisms found in fruit-packing environments and Listeria monocytogenes.

“We will study the ability of environmental microorganisms to form robust biofilms together with L. monocytogenes and how these biofilms may protect L. monocytogenes from the antimicrobial activity of sanitizers,” said Kovac, assistant professor of food science. “The data generated in this project will help improve the cleaning and sanitizing used in the fresh produce industry to better control L. monocytogenes and support the production of safe food.”

Microbiota isolated from fruit packing environments growing in lab dishes.
Microbiota isolated from fruit packing environments growing in lab dishes. Photo: Penn State.

Listeria and other microorganisms found in the natural environment, such as soil, can be introduced unintentionally into food-processing facilities with raw foods such as fruit. The research is needed, Kovac explained, because once introduced into the food-processing environment, Listeria and many other environmental microorganisms can grow on surfaces into microbial layers called biofilms.

“Microorganisms enclosed in a biofilm produce slimy substances that protect them from the antimicrobial activity of sanitizing chemicals by slowing down their penetration into the core of a biofilm,” Kovac said. “Biofilm formation can therefore result in reduced efficacy of antimicrobial sanitizers used to inactivate Listeria. This project will investigate the interactions between microorganisms found in fruit-packing environments and L. monocytogenes.”

Graduate student Laura Rolon is working on four project objectives: isolate environmental microbiota and determine their resistance to sanitizers; characterize genomes of environmental isolates using whole-genome sequencing; characterize biofilm formation ability of bacterial families and Listeria monocytogenes in single- and in multi-family assemblages; and characterize the effect of microbial assemblages on the tolerance of Listeria monocytogenes to sanitizer treatment.

“Listeria monocytogenes is especially dangerous because the pathogen can survive, grow and persist at low temperatures in produce-processing facilities,” Rolon said. “Biofilms represent a physical barrier that reduces the effective diffusion and antimicrobial action of sanitizers and is hypothesized to increase L. monocytogenes’ tolerance to sanitizers used in food processing facilities.”

The role of the food-processing environment microbiota on Listeria monocytogenes survival within a biofilm under sanitizer pressure is poorly understood, according to LaBorde. So, the researchers will evaluate the ability of the most relevant environmental microbiota found in produce- packing environments to form single- and multi-species biofilms with L. monocytogenes.

“We will measure the effect of the resulting biofilms on L. monocytogenes’ tolerance to sanitizers,” he said. “The findings of this research project will inform and enhance sanitation protocols and extension training efforts targeted at the tree-fruit industry to effectively control L. monocytogenes.”




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