An ongoing project consists of identifying the bacteria present in dairy processing environments in order to assess the impact on Listeria monocytogenes.
Teagasc in Ireland and the University of Veterinary Medicine Vienna in Austria collect samples from dairy processing plants and characterize microorganisms, with the aim of preventing the presence of harmful pathogens.
The LmRNA project is gaining an understanding of the response of Listeria monocytogenes to dairy environmental conditions. Fictional communities of microorganisms are created in the laboratory to mimic what is found in dairy environments. The role of other microorganisms is studied to determine their impact on Listeria monocytogenes.
A food processing environment is not sterile and the presence of certain microorganisms in cheese production may be desired. During dairy processing, milk components can adsorb onto surfaces, enhancing attachment and biofilm formation.
The three-year project uses a metagenomic approach, with researchers studying the microbiome of the environment, the most prevalent microorganisms and the interactions between those present in biofilms. Culture-based methods are used to isolate live bacteria from these environments.
Scientists proceed to the formation of biofilms of Listeria monocytogenes in the laboratory. They use conditions often found in the dairy industry, including low temperatures, appropriate growth media, flow regimes and surface materials such as stainless steel.
After entering a food processing environment, bacteria initiate biofilm formation with reversible attachment to a surface. Over time, these bacteria produce exopolymeric substances (EPS) that give the attachment that can only be lost if direct mechanical and chemical action is exerted.
Over time, biofilms grow and eliminate bacterial cells. This spreads bacteria and can become the source of recurrent contamination. The EPS biofilm acts as a barrier for the diffusion of antimicrobials, leading to the protection of the enclosed cells. The chemical nature of EPS often leads to the inactivation of disinfectants and cleaning agents used in the food industry.
Researchers aim to identify targets for antimicrobials, leading to improved strategies to prevent the persistence of harmful pathogens in the dairy industry.
Impact of temperature and salt on Listeria
Another study by Spanish scientists looked at Listeria in pasteurized soft milk and raw ripened sheep’s milk cheeses.
Researchers from the University of Cordoba and the University of Burgos assessed the impact of storage temperature and salt concentration on Listeria monocytogenes.
The team analyzed the products at a temperature reflecting refrigeration of the product at 4 degrees C and another based on storage at room temperature of 22 degrees C (71 degrees F). The results showed that the bacteria survived better at lower storage temperatures, according to the study published in Food Microbiology.
They found that a reduced salt concentration in soft cheeses did not affect the behavior of the microorganism.
(To sign up for a free subscription to Food Safety News, Click here.)