In food facilities, biofilms or their debris might act as
for attracting free floating microorganisms. In this sense,
, a dense biofilm producer frequently isolated from food contact surfaces, could ...be a good candidate for sheltering other microorganisms, such as
. The main objective of this work was to evaluate the ability of
to colonize pre-established
biofilms. For this, the movement throughout mature
biofilms of a green fluorescent protein (GFP) - tagged strain of
was tracked for 24 h by confocal laser scanning microscopy (CLSM). Moreover, in order to check the effect of the incorporation of
on the overall matrix production, attached populations of both microorganisms and total biomass (cells + matrix) of the resulting biofilms were measured over time. Planktonic cells of
efficiently migrated to preformed
biofilms. Moreover, they moved preferentially toward the bottom layers of these structures, suggesting some kind of tropism. When preformed
biofilms were conditioning the surfaces, the
attached population was on average, 1-2 Log higher than when this organism grew on bare coupons. Furthermore, the arrival of
to the already established
biofilms led to a matrix over-production. Indeed, biomass values optical density (OD
) of the resulting biofilms were double those of the ordinary
mixed biofilms (1.40 vs. 0.6). The fact that
cells accumulate in the bottom layers of preformed biofilms provides this microorganism an extra protection toward physical-chemical damages. This might partly explain why this microorganism can persist in food industry environments.
Bacterial biofilms mechanically behave as viscoelastic media consisting of micron-sized bacteria cross-linked to a self-produced network of extracellular polymeric substances (EPSs) embedded in ...water. Structural principles for numerical modeling aim at describing mesoscopic viscoelasticity without losing details on the underlying interactions existing in wide regimes of deformation under hydrodynamic stress. Here, we approach the computational challenge to model bacterial biofilms for predictive mechanics in silico under variable stress conditions. Up-to-date models are not entirely satisfactory due to the plethora of parameters required to make them functioning under the effects of stress. As guided by the structural depiction gained in a previous work with Pseudomonas fluorescens Jara et al., Front. Microbiol. 11, 588884 (2021), we propose a mechanical modeling by means of Dissipative Particle Dynamics (DPD), which captures the essentials of topological and compositional interactions between bacterial particles and cross-linked EPS-embedding under imposed shear. The P. fluorescens biofilms have been modeled under mechanical stress mimicking shear stresses as undergone in vitro. The predictive capacity for mechanical features in DPD-simulated biofilms has been investigated by varying the externally imposed field of shear strain at variable amplitude and frequency. The parametric map of essential biofilm ingredients has been explored by making the rheological responses to emerge among conservative mesoscopic interactions and frictional dissipation in the underlying microscale. The proposed coarse grained DPD simulation qualitatively catches the rheology of the P. fluorescens biofilm over several decades of dynamic scaling.
Listeria monocytogenes can form long-lasting biofilms on food-contact surfaces. Lactic acid bacteria (LAB) have shown promise in antagonizing this microorganism in liquid media. However, the ...ecological relationships differ when cells are forming biofilms. In this work, we propose the use of Lactobacillus biofilms as surface “conditioners” to modulate the adhesion of L. monocytogenes. For this, the biofilm formation ability of Lactobacillus fermentum MP26 and Lactobacillus salivarius MP14 (human milk origin), fluorescently labeled by transfer of the mCherry-encoding pRCR12 plasmid, was first evaluated. Then, mature biofilms of these strains transformed with pRCR12 for expressing the fluorescent protein mCherry were used as adhesion substrate for GFP-tagged L. monocytogenes Scott A. The resulting biofilms were studied in terms of cellular population and attached biomass (cells plus matrix). Species distribution inside the biofilm structure was revealed by confocal laser scanning microscopy (CLSM). Although none of the Lactobacillus spp. strains reduced the adhesion of L. monocytogenes Scott A, species interactions seem to interfere with the synthesis of extracellular polymeric substances and species distribution inside the biofilms. In dual-species biofilms, CLSM images revealed that Lactobacillus cells were trapping those of L. monocytogenes Scott A. When surfaces were conditioned with Lactobacillus biofilms, the spatial distribution of L. monocytogenes Scott A cells was species-specific, suggesting these interactions are governing the ultimate biofilm structure. The results here obtained open new possibilities for controlling L. monocytogenes dispersal using these Lactobacillus spp. biofilms as a “natural” immobilization way. Whether species interactions could modify the virulence of L. monocytogenes still remains unclear.
•L. monocytogenes Scott A can coexist in dual-species biofilms with lactobacilli.•Lactobacilli microcolonies trapped L. monocytogenes cells in dual-species biofilms.•Preformed lactobacilli biofilms improved early adhesion of L. monocytogenes.•L. monocytogenes cells can fully integrate into preformed lactobacilli biofilms.•Species distribution inside biofilms is strain-specific.
Changes in spatial organization, as observed by confocal laser scanning microscopy (CLSM), viable cell content, biovolume, and substratum surface coverage of the biofilms formed on glass by ...Pseudomonas fluorescens resulting from co-culture with Listeria monocytogenes, were examined. Two strains of L. monocytogenes, two culture temperatures and two biofilm developmental stages were investigated. Both L. monocytogenes strains, a persistently sampled isolate (collected repeatedly along 3 years from a meat factory) and Scott A, induced shrinkage in matrix volume, both at 20°C and 4°C, in mature or old biofilms, without loss of P. fluorescens cell count per surface unit. The nearly homogeneous pattern of surface coverage shown by mono-species P. fluorescens biofilms, turned into more irregular layouts in co-culture with L. monocytogenes. The upper layer of both mono and dual-species biofilms turned to predominantly consist of matrix, with plenty of viable cells underneath, in old biofilms cultured at 20°C, but not in those grown at 4°C. Between 15 and 56% of the substratum area was covered by biofilm, the extent depending on temperature, time and L. monocytogenes strain. Real biofilms in food-related surfaces may thus be very heterogeneous regarding their superficial components, i.e., those more accessible to disinfectants. It is therefore a hygienic challenge to choose an adequate agent to disrupt them.
This work presents the assessment of the effectivity of a pronase (PRN)-benzalkonium chloride (BAC) sequential treatment in removing Listeria monocytogenes-Escherichia coli dual-species biofilms ...grown on stainless steel (SS) using fluorescence microscopy and plate count assays. The effects of PRN-BAC on the occupied area (OA) by undamaged cells in 168 h dual-species samples were determined using a first-order factorial design. Empirical equations significantly (r
2
= 0.927) described a negative individual effect of BAC and a negative interactive effect of PRN-BAC achieving OA reductions up to 46%. After treatment, high numbers of remaining attached and released viable and cultivable E. coli cells were detected in PRN-BAC combinations when low BAC concentrations were used. Therefore, at appropriate BAC doses, in addition to biofilm removal, sequential application of PRN and BAC represents an appealing strategy for pathogen control on SS surfaces while hindering the dispersion of live cells into the environment.
Bacteria can form biofilms in different environmental conditions, e.g. pH, temperature, nutrients, etc. Biofilm growth, therefore, is an extremely robust process. Because of this, while biofilm ...growth is a complex process affected by several variables, insights into biofilm formation could be obtained by studying simple schematic models. In this manuscript, we describe a hybrid molecular dynamics and Monte Carlo model for the simulation of the early stage formation of a biofilm, to explicitly demonstrate that it is possible to account for most of the processes expected to be relevant. The simulations account for the growth and reproduction of the bacteria, for their interaction and motility, for the synthesis of extracellular polymeric substances and exopolisaccharide trails. We describe the effect of these processes on the early stage formation of biofilms, in two dimensions, and also discuss preliminary three-dimensional results.
Chitosan has proven antimicrobial properties against planktonic cell growth. Little is known, however, about its effects on already established biofilms. Oriented for application in food industry ...disinfection, the effectiveness of both medium molecular weight (MMW) chitosan and its enzymatically hydrolyzed product was tested against mature biofilms of four pathogenic strains, Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus and Salmonella enterica, and a food spoilage species, Pseudomonas fluorescens. Unexpectedly, log reductions were in some cases higher for biofilm than for planktonic cells. One hour exposure to MMW chitosan (1% w/v) caused a 6 log viable cell reduction on L. monocytogenes monospecies mature biofilms and reduced significantly (3-5 log reductions) the attached population of the other organisms tested, except S. aureus. Pronase-treated chitosan was more effective than MMW chitosan on all tested microorganisms, also with the exception of S. aureus, offering best results (8 log units) against the attached cells of B. cereus. These treatments open a new possibility to fight against mature biofilms in the food industry.
The polysaccharides associated with free (planktonic) and surface-attached (biofilm) cells from cultures of
Pseudomonas fluorescens strain B52 were compared. Variations in the attached matrix due to ...surface material (glass or stainless steel) were also analyzed. Two digestion methods were used to optimize the recoveries of sugars, uronic acids and acidic substituents. The yield of analyzable material after digestion reached 90% for the material associated to the biofilms, though only 20–30% for that bound to planktonic cells. The polysaccharide(s) in the biofilm had glucuronic and guluronic acids as main components, besides rhamnose, glucose and glucosamine. The proportion of glucuronic to guluronic acid was higher in the polysaccharide(s) found in biofilms formed on stainless steel than in those on glass.
Direct observation of the influence of titanium oxide (TiO2) nanoparticles on the development of Pseudomonas fluorescens biofilms on the surfaces of TiO2/polystyrene nanocomposite films was performed ...using scanning electron and atomic force microscopies. Significant reduction in the area covered by the biofilm on the nanocomposite surface was detected, as well as a decrease in the amount of extracellular polymeric substance secreted by the microorganism. The water contact angle values and surface roughness of the thermoplastic films showed negligible changes with the introduction of TiO2 nanoparticles in polystyrene, indicating that the nanostructures inhibit cellular adhesion by affecting the microorganisms directly and not by changing the surface properties of the polymer.
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•P. fluorescens biofilms were grown on TiO2/polystyrene nanocomposites.•Area covered by the biofilm on TiO2/PS was much smaller than that on neat PS films.•TiO2 nanoparticles lead to reduction of the amount of EPS in the biofilm.•Novel low-cost materials for prevention of biofilm related contaminations.
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