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, often referred as Group B Streptococcus (GBS) is a gram-positive streptococcus and originally discovered as a cause of bovine mastitis. GBS is part of the normal bacterial flora colonizing the gastrointestinal(GI) tract and genitourinary tract of a significant proportion of the human population. However, it occasionally become a infectious pathogen colonizing the uterus, blood, brain, and meninges. This pathogen is one of the leading causes of invasive infections in non-pregnant immunocompromised individuals and also causes bacteremia, septicaemia, meningitis, and pneumonia. Colonization of the rectum and vagina of pregnant women with GBS is correlated with GBS sepsis in newborn infants with early onset disease. Streptococcus agalactiae usually appears in the form of long chains and can be isolated in infected site of human or in secretions from infected mammary gland of female cattle and related ungulates. In some samples these are numerous and easily found in stained films; in other cases the organisms may be so scarce that they can be located only with great difficulty. Also, most stains can be used to stain GBS to locate them, since the GBS is gram-positive and readily stained. Streptococcus agalactiae poses a serious threat to lives of neonates, responsible for 2-3 cases per 1000 live birth and to lives of human, especially elderly persons and those with weakened immune systems. This microorganism is considered one of the major causes of economic losses to dairy producers without a control program. Because of its significance as an threat to both human and related ungulates, such as cow, its genome was sequenced and still being studied to gain more insight into the virulence factor and to develop treatments and preventive prophylactic antibodies.

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 or ganism's lifestyle?

is subclassified into nine serotypes depending on the immunologic reactivity of the polysaccharide capsule and among nine serotypes, only types Ia, Ib, II, III, and V are discovered to be responsible for invasive human disease. The entire genome of serotype III strain NEM 316 has been sequenced, since serotype III is causing significant percentage of both early and late onset diseases.

Several comparisons were made between genome of GBS and that of related pathogenic streptococci and also that of non-pathogenic species in order to find clues to the evolution of GBS and its acquisition of virulence.

Streptococci. Streptococci are Gram-positive, nonmotile, nonsporeforming, catalase-negative cocci that occur in pairs or chains. Members of this genus vary widely in pathogenic potential. Most streptococci are facultative anaerobes, and some are obligate anaerobes. The genus is classified on the basis of colony morphology, hemolysis, biochemical reactions, and serologic specificity. They are divided into three groups by the type of hemolysis on blood agar plates: beta-hemolytic, alpha-hemolytic or gamma-hemolytic. Serologic grouping is based on antigenic differences in cell wall carbohydrates, in cell wall pili-associated protein, and in the polysaccharide capsule in group B streptococci.

Streptococcus agalactiae. This organism is the leading cause of meningitis and sepsis in newborns. Additionally this organism is the cause of serious infections in immunocompromised adults. Clinical manifestations of infection include urinary tract and soft tissue infections as well as life-threatening sepsis and meningitis. Additionally S. agalactiae is able to asymptomatically colonize human skin and mucous membranes.

Streptococcus agalactiae strain NEM316. This strain is a serotype III strain isolated from a case of fatal septicemia. Type III is responsible for 80% of neonatal GBS (group B streptococcal) meningitis.


The genome of eight strains in Streptococcus agalactiae (GBS) have been completely sequenced: Streptococcus agalactiae 18RS21, Streptococcus agalactiae 2603V/R, Streptococcus agalactiae 515, Streptococcus agalactiae A909, Streptococcus agalactiae CJB111, Streptococcus agalactiae COH1, Streptococcus agalactiae H36B, Streptococcus agalactiae NEM316.

Streptococcus agalactiae NEM316 is the serotype III strain isolated from urine of a fatal case of septicaemia. Complete genome sequence of this strain is a circular DNA chromosome with 2,211,285 nt (GC content of 35%, coding content of 87%, and dsDNA) and contains 2235 genes, 2082 protein coding gens, 101 structural RNSs, and 36 pseudogenes. plasmid? Genome sequence was completed in 2002/11/15.

This strain expresses various products, such as capsular polysacci

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