The presence of undesirable biofilms on food processing contact surfaces may lead to: 1) transmission of diseases; 2) food spoilage; 3) shortened time between cleaning events; 4) contamination of product by nonstarter bacteria; 5) metal corrosion in pipelines and tanks; 6) reduced heat transfer efficacy or even obstruction of the heat equipment.Despite the significant problems caused by biofilms in the food industry, biofilm formation in these environments is still poorly understood and effective control of biofilms remains challenging. Although it is understood that cell attachment and biofilm formation are influenced by several factors, including type of strain, chemical-physical properties of the surface, temperature, growth media, and the presence of other microorganisms, some conflicting statements can be retrieved from the literature and there are no general trends yet that allow us to easily predict biofilm development. It is likely that still unexplored interaction of factors may be more critical than the effect of a single parameter.New alternative biofilm control strategies, such as biocontrol, use of enzymes and phages, and cell-to-cell communication interference, are now available that can reduce the use of chemical agents. In addition, as preventing biofilm formation is a more efficient strategy than controlling mature biofilm, the use of surface-modified materials have been suggested. These strategies may better reveal their beneficial potential when the ecological complexity of biofilms in food environments is addressed.
The study was conducted on alterations found on stone artwork and integrates microbial control and a biotechnological method for the removal of undesirable chemical substances. The Demetra and Cronos sculptures are two of 12 stone statues decorating the courtyard of the Buonconsiglio Castle in Trento (Italy). An initial inspection of the statues revealed putative black crusts and highlighted the microbial contamination causing discoloration. In 2006, the Cultural Heritage Superintendence of Trento commissioned us to study and remove these chemical and biological stains. Stereomicroscopy characterised the stone of the sculptures as oolitic limestone, and infrared analyses confirmed the presence of black crusts. To remove the black crusts, we applied a remediation treatment of sulphate-reducing bacteria, which removes the chemical alteration but preserves the original stone and the patina noble. Using traditional and biomolecular methods, we studied the putative microbial contamination and confirmed the presence of biodeteriogens and chose biocide Biotin N for the removal of the agents causing the discolouration. Denaturing gradient gel electrophoresis fluorescent in situ hybridisation established that Cyanobacteria and green algae genera were responsible for the green staining whereas the black microbial contamination was due to dematiaceous fungi. After the biocide Biotin N treatment, we applied molecular methods and demonstrated that the Cyanobacteria, and most of the green algae and dematiaceous fungi, had been efficiently removed. The reported case study reveals that conservators can benefit from an integrated biotechnological approach aimed at the biocleaning of chemical alterations and the abatement of biodeteriogens.
We exploited the ability of photocatalytic titanium dioxide (TiO(2)) as an agent for the biofilm control. Two photocatalytic systems were investigated: a 3 g L(-1) suspension of TiO(2) nanopowder in demineralized water and glass slides coated with a TiO(2) thin film, achieved by sol-gel deposition. A running protocol for the photoactivation of TiO(2) was set up using the dye rhodamine B. The microorganisms studied were Pseudomonas stutzeri, Pseudomonas aeruginosa and a Bacillus cereus-group as planktonic cells. P. aeruginosa biofilms were also studied at both the solid-liquid and the solid-air interface. The TiO(2) nanopowder produced 1-log reduction of Bacillus sp. planktonic cells in 24 h, 2-log reduction of P. stutzeri planktonic cells in 30 min and 1-log reduction of P. aeruginosa planktonic cells in 2 h compared with non-photo-activated TiO(2). TiO(2) thin film produced almost a complete eradication of P. aeruginosa planktonic cells (initial concentration 10(8) cells mL(-1)) in 24 h compared to a 3-log reduction caused by UV-A light alone. In contrast, neither the photocatalytic treatment with TiO(2) film nor that with TiO(2) nanopowder had any effect on P. aeruginosa biofilms at all the interfaces investigated. Possible explanations for these findings, and for the discrepancy between this work and literature data, are discussed.
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