Apple-processing facility research to improve pathogen control

Apple-processing facilities, in which Listeria monocytogenes has been persistent, have been under research in order to improve pathogen control in the apple supply chain.

Penn State research suggests that pathogenic bacteria in apple-packing facilities may be sheltered and protected by harmless bacteria known for its ability to form biofilms.

The study researched three fruit-packing facilities in the US where contamination with Listeria monocytogenes was a concern. With the collaboration of the apple industry, the aim of the research was to understand the microbial ecology of food processing facilities. The ultimate goal is to improve pathogen control in the apple supply chain in order to avoid foodborne disease outbreaks and recalls of apples and apple products.

“This work is part of Penn State’s efforts to help producers comply with standards set forth in the federal Food Safety Modernisation Act, often referred to as FSMA,” said researcher Jasna Kovac, assistant professor of food science at the College of Agricultural Sciences.

As part of the study, researchers analysed the composition of microbiota in apple-packing environments and its association with the occurrence of Listeria monocytogenes. The research revealed that packing plants with higher Listeria monocytogenes occurrences were dominated by the bacterial family Pseudomonadaceae and the fungal family Dipodascaceae.

Researchers collected samples in apple-packing facilities in which Listeria monocytogenes has been persistent. Credit: Penn State

Studying the properties of the microorganisms revealed them to be good biofilm formers. “Based on our findings, we hypothesise that these harmless microorganisms are supporting the persistence of Listeria monocytogenes because they protect the harmful bacteria by enclosing them in biofilms. We are testing this hypothesis in a follow-up study,” said lead researcher Xiaoqing Tan, a member of the Penn State Microbiome Centre.

Xiaoqing Tan tests bacteria samples from apple-processing plants in the laboratory. Credit: Penn State

Biofilms are microorganisms that attach to a surface and then release a slimy material that affects the penetration of cleaners and sanitisers. “If a pathogenic bacterium is enclosed in a biofilm formed by microbiota, it is more likely that cleaning and sanitising procedures will be less effective,” Kovac said. “This may well explain how Listeria monocytogenes has persisted in food-processing plants despite repeated efforts to kill and remove it.”

Published in Microbiome, the findings of the research provide insight into the Listeria contamination problem and could lead researchers and the apple industry closer to solving it. Kovac pointed out that a key factor causing the development of Listeria monocytogenes is the equipment in fruit-processing plants, such as brush conveyors, which can be difficult to clean and sanitise.

Kovac’s team of researchers is experimenting with some of the non-pathogenic strains of bacteria that are not harmful to humans, to determine if they can be used as biocontrols.

“Once applied on the surfaces of the equipment in these environments, they may be able to outcompete and suppress Listeria, thus reducing food-safety risks and potential regulatory action. We are still exploring that approach in a controlled laboratory environment. If it proves to be feasible, we would like to test it in apple-packing and processing facilities,” Kovac said.

It is suspected that the challenges presented by microbiota hiding Listeria monocytogenes are not limited to fruit-processing facilities or produce. Penn State researchers are now set to investigate microbial communities in dairy processing facilities, to determine the microbial composition and ecology of these environments.

Top image credit: Brian Holsclaw.