Identification and molecular characterization of a S. agalactiae strain lacking the capsular locus

Eur J Clin Microbiol Infect Dis. 2012 Mar;31(3):233-5. doi: 10.1007/s10096-011-1298-7. Epub 2011 May 26.


During a national surveillance program on Group B streptococci (GBS) maternal carriage and neonatal infections, a GBS strain isolated from a pregnant woman's vagino-rectal swab was non typable by either serological or molecular methods. Further molecular characterization demonstrated that the strain lacked the entire capsular locus, possibly by a recombination event that excised a 14,1 Kbase pairs genomic fragment extending from the regulatory protein cpsX gene to the neuA gene. The natural loss of the capsular locus by GBS isolated from a human has never been described so far. Such an event, while possibly a dead-end from the evolutionary point of view, leaves a still able-to-colonize organism unrecognizable by the vaccines currently under development.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Capsules / genetics*
  • DNA Primers
  • Female
  • Humans
  • Polysaccharides, Bacterial / metabolism*
  • Pregnancy
  • Pregnancy Complications, Infectious / microbiology
  • RNA, Ribosomal, 16S / genetics
  • Restriction Mapping
  • Sequence Analysis, DNA
  • Streptococcal Infections / microbiology
  • Streptococcus agalactiae / classification
  • Streptococcus agalactiae / genetics*
  • Streptococcus agalactiae / isolation & purification
  • Vagina / microbiology


  • DNA Primers
  • Polysaccharides, Bacterial
  • RNA, Ribosomal, 16S