The nutritional requirements for biofilm formation by Group A streptococcus

Using a crystal violet assay, we tested the ability of 84 group A streptococcal (GAS) strains representing more than 50 different emm-types to form biofilms. Our data demonstrate that almost all strains under investigation (83 of 84) were able to form biofilms to some degree. Biofilm forming capacity was in general conserved among isolates of the same emm-type. Biofilm formation was not altered by carbon dioxide or sucrose. However, increased glucose concentration resulted in increased biofilm formation. As growth in the presence of glucose has also been reported to reduce virulence factor expression, we hypothesise that the biofilm mode of growth may be associated with evasion of host immune responses.