Streptococcus agalactiae

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A Microbial Biorealm page on the genus Streptococcus agalactiae


Higher order taxa

cellular organisms; Bacteria; Firmicutes; Bacilli; Lactobacillales; Streptococcaceae; Streptococcus


NCBI: Taxonomy

Streptococcus agalactiae

Description and significance

Describe the appearance, habitat, etc. of the organism, and why it is important enough to have its genome sequenced. Describe how and where it was isolated. Include a picture or two (with sources) if you can find them.

Streptococcus agalactiae Streptococcus agalactiae, also referred to as Group B Streptococcus, is Gram-positive cocci, ~2.0 µm occurring in pairs and short chains characterized by the presence of group B Lancefield antigen. It is facultatively anaerobic and a B heamolytic strep.

Streptococcus agalactiae is also a obligate pathogen that affects pre-milking heifers, as well as older cows in dairy herds. It is considered one of the major causes of economic losses to dairy producers without a control program.

These bacteria, causing Group B streptococcal infection, is a commensal bacterium colonizing the intestinal track of a significant proportion of the human population. Normal habitats are the gut and female urogenital tract.

It can be isolated from Bovine Mastitis or from infants for clonal analysis.

Identification was performed by cultural, biochemical and serological properties and by polymerase chain reaction amplification of species-specific parts of the gene encoding the 16S rRNA, the 16S–23S rDNA intergenic spacer region and the CAMP factor (cfb) gene.

Genome structure

Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence? Does it have any plasmids? Are they important to the organism's lifestyle?

The genome is 2 211 485 bases pairs long and contains 2118 protein coding genes.

Strains within S. agalactiae:

The genome of S. agalactiae strain NEM316, responsible for a fatal case of septicaemia, consists of a circular chromosome of 2 211 485 base pairs (bp). G+C content of genome is 35.6%, which is significantly lower than that of the genomes of S. pyogenes (38.5%) and of S. pneumoniae (39.7%). Seven sets of ribosomal RNA (23S, 5S and 16S) were identified to be organized within a 450kb region located on the right replichore of the chromosome next to the origin of replication (figure). 80 tRNA genes are identified, which recognize 31 out of 61 possible sense codons. The genome of strain NEM316 contains 2082 protein coding genes with 36 pseudogens. the gene orientation was observed to be strongly biased, as 81% of the coding sequences (CDS) are transcribed in the same orientation as the movement of the replication fork. This characteristic bias of gene orientation appears to be common feature of low G+C Gram positive bacteria.

Even though no complete genetic material of bacteriophage was identified in this strain NEM316 gene, it was observed that there are a large number of plasmid- and phage-related genes. 12 genes were identified to be related to plamid function (replication, partition or transfer) which are often found near integrase genes, while 12 genes were identified to encode proteins similar to phage integrase, which is an enzyme that facilitates prophage integration into or excision from a bacterial chromosome.

Cell structure and metabolism

Describe any interesting features and/or cell structures; how it gains energy; what important molecules it produces.


Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.


How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

S. agalactiae is a pathogen which is the leading cuase of invasice infections in neonates and causes septicaemia, meningitis and pneumonia (in adults, osteomyelitis, septic arthritis, postpartum sepsis, amnionitis, urinary tract infection, and still birth. )

S. agalactiae expresses a variety of extracellular products, implicated in vriulence. These includes the capsular polysacchardie, surface proteins and secreted protein. Two distinct polysaccharide antigens of the sialylated capsular polysaccharide, one of the most important S. agalactiae virulence factors, are possessed. This inhibits deposition of the host complement factor C3b and thus, complement-mediated opsonophagocytosis. Surface proteins plays an crucial rile during the infectious process by mediating interactions between the pahigen and the host cells and/or evasion for the host defense. The polysaccharide antiphagocytic capsule is this bacterium's main virulence factor.

"Associated with diseases of the newborn; 90% of cases have septicemia, 40% have pulmonary involvement, and 30% have meningeal involvement; early onset disease acquired in utero or during passage through the birth canal and can have a case fatality rate of 50%; late onset disease with onset from 1 week to 3 months after birth have a case fatality rate of 20% and are probably acquired from the environment: survivors of meningitis cases can be left with hearing loss, blindness, cerebral palsy, mental retardation and/or epilepsy; adult infections include pneumonia, urinary tract infection, peritonitis, meningitis, endocarditis, osteomyelitis and rarely pharyngitis"

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

Current Research

Enter summaries of the most recent research here--at least three required


Philippe Glaser, Christophe Rusniok, Carmen Buchrieser, Fabien Chevalier, Lionel Frangeul, Tarek Msadek, Mohamed Zouine, Elisabeth Couvé, Lila Lalioui, Claire Poyart, Patrick Trieu-Cuot, Frank Kunst "Genome sequence of Streptococcus agalactiae, a pathogen causing invasive neonatal disease".Molecular Microbiology. 2002. 45 (6), 1499–1513.doi:10.1046/j.1365-2958.2002.03126.x

[Ferretti, J.J., McShan, W.M., Ajdic, D., Savic, D.J., Savic, G.,Ferretti, J.J., McShan, W.M., Ajdic, D., Savic, D.J., Savic, G., M1 strain of Streptococcus pyogenes. Proc Natl Acad Sci USA 98: 4658–4663.]

[Tettelin, H., Nelson, K.E., Paulsen, I.T., Eisen, J.A., Read, T.D., Peterson, S., et al. (2001) Complete genome sequence of a virulent isolate of Streptococcus pneumoniae. Science 293: 498–506.]

[ John F. Bohnsack,* April A. Whiting,* Gabriela Martinez,† Nicola Jones,‡ Elisabeth E. Adderson,§ Shauna Detrick,* Anne J. Blaschke-Bonkowsky,* Naiel Bisharat,‡ and Marcelo Gottschalk† " Serotype III Streptococcus agalactiaefrom Bovine Milk and Human Neonatal Infections".Emerging Infectious Diseases • Vol. 10, No. 8, August 2004]


Edited by Ha Bean Kim,student of Rachel Larsen and Kit Pogliano