Streptococcus agalactiae

Taxobox
color = lightgrey
name = "Streptococcus agalactiae"


image_width = 240px
image_caption =
regnum = Bacteria
phylum = Firmicutes
classis = Bacilli
ordo = Lactobacillales
familia = Streptococcaceae
genus = "Streptococcus"
species = "S. agalactiae"
binomial = "Streptococcus agalactiae"
binomial_authority = Lehmann and Neumann, 1896

"Streptococcus agalactiae" also known as Group B Streptococcus (GBS) and more colloquially as Strep B and group B Strep is a gram-positive streptococcus characterized by the presence of group B Lancefield antigen. These bacteria cause Group B streptococcal infection. Streptococcus agalactiae is a species of the normal flora of the gut and female urogenital tract. GBS infection occur as early onset disease of the neonate on day 1-7 after birth or late onset disease on day 7-90. Perinatal infection causes septicemia, pneumonia or meningitis, which are associated with a high mortality. During delivery, a baby can acquire "S. agalactiae" and develop neonatal sepsis, neonatal meningitis, and/or neonatal pneumonia. Neonates with meningitis do not present with the hallmark sign of adult meningitis, a stiff neck. They display nonspecific symptoms such as fever, vomiting, poor feeding, and irritability. Invasive GBS disease of the adult is seen in pregnant women, immuncompromisied individuals such as diabetics or in elderly. The polysaccharide antiphagocytic capsule is this bacterium's main virulence factor.

"S. agalactiae" displays beta-hemolysis when cultured on a blood agar plate and produce zones of hemolysis that are only slightly larger than the colonies themselves. Group B streptococci hydrolyze sodium hippurate and give a positive response in the CAMP test. "S. agalactiae" is also sensitive to bile and will lyse in its presence.

In the western world GBS is the most important reason for bacterial septicemia of the newborn. Death or long term sequelae such as haring loss can follow. Although up to 1/3 of women in childbearing age are carriers of the bacterium only very few newborns will get sick by GBS (ca. 1/1.000 live births). Prevention of the disease is a matter of debate. Vaccination of adolescent women is expected to be a solution for the problem. Research for the development of such a vaccine is underway, but has so far not produced a good candidate vaccine. In the meantime prevention measures with antibiotic prophylaxis given during delivery are used. Different western countries have different strategies for selection of women in labour that should get antibiotics. The most aggressive strategy is used in the USA with general screening for GSB in pregnancy week 35-37 and antibiotic prophylaxis given to all positive women. This strategy has given a marked reduction in babies with early onset disease. Most European countries do not screen generally but use a risk based strategy at time of delivery.

References

*Brooks, Geo F., Janet Butel, and Stephen Morse. Jawetz, Melnick, and Adelberg's Medical Microbiology, 22nd edition. 2001.
*Gillespie, Stephen and Kathleen Bamford. Medical Microbiology at a Glance. 2000.

External links

* [http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5111a1.htm Prevention of Perinatal Group B Streptococcal Disease] August 16, 2002 MMWR 2000;49:228-232.
* [http://www.strepb.ca/home.htm The Canadian Strep B Foundation]
* [http://www.gbss.org.uk The UK Group B Strep Support charity]