Abstract
The objective of this study was to determine the impact of manganese (Mn2+) and heme on the biofilm formation characteristics of six B. cereus food isolates and two reference strains (ATCC 10987 and ATCC 14579). The data obtained from the crystal violet assay revealed that addition of a combination of Mn2+ and heme to BHI growth medium induced B. cereus biofilm formation. However, the induction of biofilm formation was strictly strain-dependent. In all of the induced strains, the impact of Mn2+ was greater than that of heme. The impact of these two molecules on the phenotypic characteristics related to biofilm formation, such as cell density, sporulation and swarming ability, was determined in a selected food isolate (GIHE 72–5). Addition of Mn2+ and heme to BHI significantly (p < 0.05) increased the number of cells, which was correlated with the results of crystal violet assays as well as scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) analyses. In addition, induced biofilms showed higher numbers of spores and greater resistance to benzalkonium chloride. The swarming ability of B. cereus planktonic cells was increased in the presence of Mn2+ and heme in BHI. The expression levels of a number of selected genes, which are involved in mobility and extracellular polymeric substances (EPS) formation in B. cereus, were positively correlated with biofilm formation in the presence of Mn2+ and heme in BHI. These results further confirming the role of these molecules in swarming mobility and making matrix components related to B. cereus biofilm formation. These data indicate that signaling molecules present in the food environment might substantially trigger B. cereus biofilm formation, which could pose a threat to the food industry.
Highlights
Bacterial biofilms are surface-attached multicellular communities enclosed by extracellular polymeric substances (EPS) [1]
Biofilms were grown on SS coupons with or without Mn2+ and/or heme in brain heart infusion (BHI) supplemented with glucose or glycerol
Higher crystal violet values were obtained for the GIHE 72–6, GIHE 72–7 and GIHE 72–8 isolates grown in BHI supplemented with Mn2+, heme and glycerol (BHI+Gly+Mn+Heme), the values were lower than the threshold values for biofilm formation (OD 0.3 at 595 nm)
Summary
Bacterial biofilms are surface-attached multicellular communities enclosed by extracellular polymeric substances (EPS) [1]. Biofilm formation is significant in the food industry and in the environment as biofilms are very difficult to remove from attached surfaces and are resistant to disinfectants compared to their free-floating planktonic counterparts [2]. Bacterial biofilm formation can be influenced by a number of environmental factors, including nutrient composition, metabolites and co-factors present on attachment surfaces, and signaling molecules produced by bacteria [3,4,5]. Impact of Mn+2 and heme on B. cereus biofilm formation
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