Scientists expand knowledge of Listeria and biofilms

Researchers have looked into the behavior of Listeria monocytogenes related to biofilms and how they support the persistence of the pathogen in food processing environments.

A study led by the Austrian Competence Centre for Feed and Food Quality, Safety and Innovation (FFoQSI) found that Listeria monocytogenes can colonize existing biofilms and it also survives in them.

Microorganisms mainly live in communities protected by a self-produced matrix of extracellular polymeric substances (EPS). Within these so-called biofilms, microbial cells show altered phenotypes and gene expression patterns. The self-produced common matrix serves as a protective shield, nutrient source and provides space for genetic exchange.

Listeria monocytogenes can survive in the food production environment for years. Biofilms may provide a niche for long-term survival as they protect against environmental fluctuations and disinfectants.

First study author, Eva Voglauer from FFoQSI, said: “Our data suggest that Listeria monocytogenes can colonize in multispecies biofilms, which could increase survivability to cleaning and disinfection in food processing plants and support persistence.”

A study published in the journal Microbiological Research, found that the bacterial and matrix composition of biofilms is not significantly altered by the presence of Listeria monocytogenes, which indicates Listeria hides in the biofilm. This observation could change the view on Listeria monocytogenes as an active player in the processing environment to a passive survivor and resident of biofilms.

Protection by other bacteria
Scientists investigated the behavior of an isolate of Listeria monocytogenes in a multispecies biofilm. This consisted of Pseudomonas fragi, Brochothrix thermosphacta, and Carnobacterium maltaromaticum. Within the meat sector, these three possible spoilage bacteria have been isolated frequently. Listeria was able to colonize the multispecies biofilm within two hours.

The selected Listeria monocytogenes strain with sequence type (ST) 121 was repeatedly isolated from an Austrian meat processing facility. It had colonized the production line of the company for at least one year. Composition of the biofilm community and the matrix as well as the transcription activity were analyzed.

Biofilm growth under food processing environment conditions was mimicked on a surface of stainless steel, under low temperature of 10 degrees C (50 degrees F), and using a limited but repeated nutrient supply. After growing a multispecies biofilm for 24 hours, scientists introduced the Listeria monocytogenes strain and investigated the biofilm composition and gene expression.

“Listeria monocytogenes colonized the multispecies biofilm and accounted for 6.4 percent of all biofilm cells after six hours. Transcriptomic analysis revealed that 127 genes of Listeria monocytogenes were significantly upregulated compared to the inoculum, including genes related to motility, chemotaxis, iron and protein transport,” said scientists.

The team monitored biofilm development over six and 24 hours and seven days. Pseudomonas fragi remained the dominant species, while Listeria monocytogenes was able to survive in the multispecies biofilm accounting for 2.4 percent of total biofilm cells after seven days.

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