Acidic pH strongly enhances in vitro biofilm formation by a subset of hypervirulent ST-17 Streptococcus agalactiae strains

Appl Environ Microbiol. 2014 Apr;80(7):2176-85. doi: 10.1128/AEM.03627-13. Epub 2014 Jan 31.


Streptococcus agalactiae, also known as group B Streptococcus (GBS), is a primary colonizer of the anogenital mucosa of up to 40% of healthy women and an important cause of invasive neonatal infections worldwide. Among the 10 known capsular serotypes, GBS type III accounts for 30 to 76% of the cases of neonatal meningitis. In recent years, the ability of GBS to form biofilm attracted attention for its possible role in fitness and virulence. Here, a new in vitro biofilm formation protocol was developed to guarantee more stringent conditions, to better discriminate between strong-, low-, and non-biofilm-forming strains, and to facilitate interpretation of data. This protocol was used to screen the biofilm-forming abilities of 366 GBS clinical isolates from pregnant women and from neonatal infections of different serotypes in relation to medium composition and pH. The results identified a subset of isolates of serotypes III and V that formed strong biofilms under acidic conditions. Importantly, the best biofilm formers belonged to serotype III hypervirulent clone ST-17. Moreover, the abilities of proteinase K to strongly inhibit biofilm formation and to disaggregate mature biofilms suggested that proteins play an essential role in promoting GBS biofilm initiation and contribute to biofilm structural stability.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / metabolism
  • Bacteriological Techniques / methods
  • Biofilms / growth & development*
  • Endopeptidase K / metabolism
  • Female
  • Humans
  • Hydrogen-Ion Concentration
  • Infant, Newborn
  • Mass Screening / methods
  • Pregnancy
  • Proteolysis
  • Streptococcal Infections / microbiology
  • Streptococcus agalactiae / drug effects*
  • Streptococcus agalactiae / isolation & purification
  • Streptococcus agalactiae / physiology*


  • Bacterial Proteins
  • Endopeptidase K