Biofilm Formation by Staphylococcus aureus Clinical Isolates is Differentially Affected by Glucose and Sodium Chloride Supplemented Culture Media

<i>Staphylococcus aureus</i> (<i>S. aureus</i>) causes persistent biofilm-related infections. Biofilm formation by <i>S. aureus</i> is affected by the culture conditions and is associated with certain genotypic characteristics. Here, we show that glucose and sodium chloride (NaCl) supplementation of culture media, a common practice in studies of biofilms <i>in vitro</i>, influences both biofilm formation by 40 <i>S. aureus</i> clinical isolates (methicillin-resistant and methicillin-sensitive <i>S. aureus</i>) and causes variations in biofilm quantification. Methicillin-resistant strains formed more robust biofilms than methicillin-sensitive strains in tryptic soy broth (TSB). However, glucose supplementation in TSB greatly promoted and stabilized biofilm formation of all strains, while additional NaCl was less efficient in this respect and resulted in significant variation in biofilm measurements. In addition, we observed that the ST239-SCC<i>mec</i> (Staphylococcal Cassette Chromosome <i>mec</i>) type III lineage formed strong biofilms in TSB supplemented with glucose and NaCl. Links between biofilm formation and accessory gene regulator (<i>agr</i>) status, as assessed by δ-toxin production, and with mannitol fermentation were not found. Our results show that TSB supplemented with 1.0% glucose supports robust biofilm production and reproducible quantification of <i>S. aureus</i> biofilm formation <i>in vitro</i>, whereas additional NaCl results in major variations in measurements of biofilm formation.