Abstract
Staphylococcus (S.) xylosus is a coagulase-negative Staphylococcus species naturally present in food of animal origin with a previously described potential for biofilm formation. In this study we characterized biofilm formation of five selected strains isolated from raw fermented dry sausages, upon different growth conditions. Four strains exhibited a biofilm positive phenotype with strain-dependent intensities. Biofilm formation of S. xylosus was influenced by the addition of glucose, sodium chloride and lactate to the growth medium, respectively. It was further dependent on strain-specific cell surface properties. Three strains exhibited hydrophobic and two hydrophilic cell surface properties. The biofilm positive hydrophilic strain TMW 2.1523 adhered significantly better to hydrophilic than to hydrophobic supports, whereas the differences in adherence to hydrophobic versus hydrophilic supports were not as distinct for the hydrophobic strains TMW 2.1023, TMW 2.1323, and TMW 2.1521. Comparative genomics enabled prediction of functional biofilm-related genes and link these to phenotypic variations. While a wide range of biofilm associated factors/genes previously described for S. aureus and S. epidermidis were absent in the genomes of the five strains analyzed, they all possess the gene encoding biofilm associated protein Bap. The only biofilm negative strain TMW 2.1602 showed a mutation in the bap sequence. This study demonstrates that Bap and surface hydrophobicity are important factors in S. xylosus biofilm formation with potential impact on the assertiveness of a starter strain against autochthonous staphylococci by competitive exclusion during raw sausage fermentation.
Highlights
Staphylococcus (S.) xylosus is a Gram-positive, coagulase negative species often found on mammal skin
The only hydrophilic biofilm positive S. xylosus strain (TMW 2.1523) on the other hand adhered distinctly better to hydrophilic than to the hydrophobic support. This is in accordance with previous studies, which have proven that bacteria with hydrophobic surface properties adhere generally well to both kinds of supports while hydrophilic strains prefer hydrophilic supports (Heilmann et al, 1996a; Planchon et al, 2006)
Hydrophobic interactions are an important factor for adhesion, and cell surface hydrophobicity is influenced by a combination of the activity of autolysins such as AtlE, teichoic acids, cell surface structures, and surface net charge as well as components of the growth medium (Heilmann et al, 1997; Gross et al, 2001; An and Friedman, 2010)
Summary
Staphylococcus (S.) xylosus is a Gram-positive, coagulase negative species often found on mammal skin. S. xylosus is widely used as starter organism in raw sausage fermentations (Vos et al, 2009) and has been described as biofilm producer in the past (Planchon et al, 2006; Xu et al, 2017) This ability can be positively associated with food fermentation processes, as adhesion and biofilm formation may increase the assertiveness of a starter organism against the autochthonous. Biofilm accumulation sets in with cells adhering to each other and producing a matrix in which they are embedded in This extracellular matrix is usually composed of polysaccharides, proteins, and eDNA (Flemming and Wingender, 2010). Members of the Bap family are known to be involved in adhesion and biofilm forming processes (Latasa et al, 2006) and comprise among others Bhp, a surface protein often found in S. epidermidis (Tormo et al, 2005) and Esp, a surface protein found in Enterococcus faecalis (Shankar et al, 1999)
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