Abstract
The biofilm mode of growth protects bacterial cells against currently applied disinfection methods for abiotic (food) contact surfaces. Therefore, innovative methods, such as Cold Atmospheric Plasma (CAP), should be investigated for biofilm inactivation. However, more knowledge is required concerning the influence of the biofilm age on the inactivation efficacy in order to comment on a possible application of CAP in the (food) processing industry. L. monocytogenes and S. Typhimurium biofilms with five different ages (i.e., 1, 2, 3, 7, and 10 days) were developed. For the untreated biofilms, the total biofilm mass and the cell density were determined. To investigate the biofilm resistance towards CAP treatment, biofilms with different ages were treated for 10 min and the remaining cell density was determined. Finally, for the one-day old reference biofilms and the most resistant biofilm age, complete inactivation curves were developed to examine the influence of the biofilm age on the inactivation kinetics. For L. monocytogenes, an increased biofilm age resulted in (i) an increased biomass, (ii) a decreased cell density prior to CAP treatment, and (iii) an increased resistance towards CAP treatment. For S. Typhimurium, similar results were obtained, except for the biomass, which was here independent of the biofilm age.
Highlights
Biofilms have been defined as a structured community of bacterial cells within a self-produced matrix of polymeric substances, which is attached to an inert or living surface [1].Biofilms are omnipresent in nature and in many industrial environments, causing economic and health related problems, such as contamination/spoilage of food products, an impeded heat transfer in heatAppl
The total biofilm mass and the cell density of the untreated L. monocytogenes biofilms following 1, 2, 3, 7, and 10 day(s) of incubation at 30 ◦ C have been determined and the obtained results have been presented in Figures 2a and 3a, respectively
Important to notice that there is a high variability in OD for the seven and 10 days old L. monocytogenes biofilms (Figure 2a), which can be explained based on visual observations when performing the crystal violet staining
Summary
Biofilms have been defined as a structured community of bacterial cells within a self-produced matrix of polymeric substances, which is attached to an inert (abiotic) or living (biotic) surface [1].Biofilms are omnipresent in nature and in many industrial environments, causing economic and health related problems, such as contamination/spoilage of food products, an impeded heat transfer in heatAppl. With respect to contamination of food products, it has become clear that pathogenic bacteria, such as Listeria monocytogenes, Salmonella spp., Campylobacter jejuni, and Yersinia enterocolitica, grow predominantly as biofilms on (a)biotic surfaces rather than as planktonic cells or colonies [6,7]. These pathogenic species were mainly responsible for the foodborne illnesses reported in 2015 within the European Union [8]. Listeriosis (mainly caused by L. monocytogenes) has a relatively low notification rate (0.46/100,000 capita), but a very high fatality rate (17.7%) [8]
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