Lactobacillus ssp. are generally associated with their beneficial roles in food fermentation processes but representatives of this genus are also known to the food producing industry as spoilage bacteria.
Spoilage of industrially produced food products can often be linked to the presence of biofilms on processing equipment. Biofilms are microorganisms attached to a substratum and embedded in a matrix (1). These industrial biofilms are problematic to the food industry as the microorganisms imbedded in it often display increased resistance against cleaning agents and disinfectants. Detachment or rupture of the biofilm can lead to recontamination of food products in processing lines.
To understand the mechanisms underlying biofilm formation of Lactobacillus ssp., its impact on the development of heterogeneity and resistance and outgrowth performance. This will be assessed by using Lactobacillus plantarum WCFS1 as a model strain, next to factory and food isolates of Lactobacillus ssp. This information may provide new leads to prevent domestication and establishment of spoilage Lactobacillus spp. and to develop more effective strategies to eradicate persisters from factory environments.
Biofilm formation has been evaluated using different surfaces and media in order to set up a system which will allow the study of static biofilms. This set-up was tested using L. plantarum WCFS1. The surfaces tested were polystyrene (PS), stainless steel (SS) as well as glass (G). The performance was assessed in different media including plant- and meat-based broths such as TSB, AOAC, BHI (supplemented with glucose and Mn), MRS, and chemically defined media (CDM). Supplemented BHI and CDM were found to be the most suitable for studying biofilm formation onto the selected contact surfaces. The biofilm formation capacity of industrial isolates was then performed for SS and PS surfaces and a selection of high and low biofilm formers was made in order to study factors and mechanisms involved in more detail.
Investigate the impact of (an)aerobic, microaerophilic and respiration growth modes on biofilm formation. Adaptive (oxidative) stress response will also be assed for the different growth modes, as it has been shown previously that respiration mode increases cellular robustness. To elucidate molecular mechanisms involved in biofilm formation, transcriptome analysis (RNAseq) and relevant phenotypes will be assessed for WCFS1 and targeted mutants. Also the impact of a biofilm lifestyle on the generation of genotypic and phenotypic diversity and the occurrence of (genetic) variants with altered resistance towards preservation and disinfection will be assessed as it has a great relevance for the food industry.
Total biofilm formation was highest for L. plantarum WCFS1 and some food and factory isolates, although cell counts were in a similar range. This points to diversity in capacity to form submerged biofilms linked to production of matrix components. Use of CDM will allow testing the effect of single component variation(s) such as carbon sources on biofilm formation. The contact surfaces which allow a higher biofilm formation are SS and PS, this will be of high relevance due to the use of these materials in the food industry.
1. Watnick, P., and R. Kolter. 2000. J Bacteriol 182:2675-2679.