This study aimed to identify an approach that can simultaneously prevent biofilm-associated damage from Staphylococcus aureus, the most prevalent agent of mastitis in cattle in Algeria and dairy product spoiler, and improve the properties of dairy starters and probiotics. Selected strains Streptococcus thermophilus CNRZ 447 and methicillin-resistant S. aureus ATCC 43300 were cultured independently in broth containing increasing concentrations of gallic acid. S. aureus ATCC 43300 was shown to be an exopolysaccharide-independent biofilm producer. Gallic acid exhibited a dose- and strain-dependent antimicrobial, antibiofilm, and probiofilm effects. The molecule of gallic acid improved the exopolysaccharide production ability of S. thermophilus and altered adhesion determinants (e.i., auto-aggregation and surface hydrophobicity) of both strains. This study indicated that biofilm-associated phenotypic characteristics, such as the composition of the extracellular structure, should be determinant in the action of gallic acid on microorganisms. The intriguing stimulation of S. aureus ATCC 43300 biofilm by gallic acid could not allow us to conclude on its use as a biofilm preventing compound. Nonetheless, gallic acid was demonstrated to be a potent antimicrobial compound against S. aureus and an enhancer of biofilm phenotypic characteristics (including adhesion properties and exopolysaccharide production) of S. thermophilus. These observations suggest that gallic acid or related phenolic compounds can be used to improve the properties of probiotics and the performance of microbial cell factories. Subsequently, gallic-acid adapted S. thermophilus cultures could be explored to disperse S. aureus in dairy products and industrial materials

Staphylococcus aureus, Streptococcus thermophilus, gallic acid, biofilm, exopolysaccharide, hydrophobicity, adhesion