Streptococcus agalactiae (also known as Group B streptococcus or GBS) is a beta-hemolytic Gram-positive

Gram-positive

Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain and appearing red or pink...

 streptococcus

Streptococcus

Streptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning...

.

Identification

The CAMP test

CAMP test

The CAMP test is a test to identify Group B β-streptococci based on their formation of a substance that enlarges the area of hemolysis formed by β-hemolysin from Staphylococcus aureus...

 is an important test for identification. GBS (group B Streptococcus species) are screened through this test.
It is characterized by the presence of group B Lancefield

Rebecca Lancefield

Rebecca Craighill Lancefield was a prominent American microbiologist. She joined the Rockefeller Institute for Medical Research in New York in 1918, and was associated with that institute throughout her long and outstanding career. Her bibliography comprises more than 50 publications published...

 antigen and by its ability to hydrolyze sodium hippurate.

It is also sensitive to bile

Bile

Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...

, and will lyse

Lysis

Lysis refers to the breaking down of a cell, often by viral, enzymic, or osmotic mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a "lysate"....

 in its presence.

S. agalactiae's polysaccharide antiphagocytic capsule is its main virulence factor

Virulence

Virulence is by MeSH definition the degree of pathogenicity within a group or species of parasites as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host. The pathogenicity of an organism - its ability to cause disease - is determined by its...

.

Clinical significance

S. agalactiae is a member of the gastrointestinal normal flora in some humans and can spread to secondary sites - including the vagina in 10–30% of women. This is of clinical importance: S. agalactiae can be transferred to a neonate passing through the birth canal and can cause serious group B streptococcal infection. In the western world, S. agalactiae is the major cause of bacterial septicemia of the newborn, which can lead to death or long-term sequelae. S. agalactiae invades via alveolar and pulmonary epithelial cells; newborns are especially susceptible to infection because they lack alveolar macrophages to prevent invasion. Newborn GBS disease is separated into early-onset disease occurring on living days 0–7 and late-onset disease which starts on days 7–90. Early-onset septicemia is more prone to be accompanied by pneumonia, while late-onset septicimia is more often accompanied by meningitis. S. agalactiae neonatal meningitis does often not present with the hallmark sign of adult meningitis, a stiff neck; rather, it presents with nonspecific symptoms, such as fever, vomiting and irritability, and can consequently lead to late diagnosis. Hearing loss can be a long-term sequela of GBS-meningitis. Infection with GBS is the cause of some instances of stillbirth.

S. agalactiae is present in up to one-third of women of childbearing age, and 1.8 cases per 1000 live births will be affected by group B streptococcal infection. In the elderly or persons with compromised immune systems, septicemia or other serious infections are seen. This can also occur during pregnancy or maternity. by shafat ahmad ..lab technologist

Prevention

There is no reliable way to prevent newborn disease, currently; however, prophylactic treatment with antibiotics (typically intravenous penicillin

Penicillin

Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....

) during delivery can prevent early-onset disease. Vaccination

Vaccination

Vaccination is the administration of antigenic material to stimulate the immune system of an individual to develop adaptive immunity to a disease. Vaccines can prevent or ameliorate the effects of infection by many pathogens...

 of adolescent women is considered an ideal solution; though research for the development of such a vaccine is underway, a good candidate vaccine has yet to surface.

Different western countries use different strategies to select which women in labor are most likely to need antibiotics.

• The United States uses the most effective strategy: all pregnant women are screened for S. agalactiae and prophylactic antibiotics are given to all women testing positive . Because of this strategy, the US has seen a marked reduction in babies born with early-onset infection.
• Increasingly, European countries are screening pregnant women routinely for GBS, including in France, Germany, Italy, Spain and Slovenia, with others offering a risk-based strategy at time of delivery, including the UK, Belgium and the Netherlands.
• Part of the neonatal care in Mexico includes undergoing a screening with culture of a cervicovaginal swab during the third trimester of pregnancy, though chemoprophylaxis based on positive results remains below 50%.

Nonhuman infections

S.agalactiae has been found in many mammals such as camels, dogs, cats, crocodiles, seals or dolphins.

Cattle

S.agalactiae was recognised as a pathogen in cattle before the Second World War. Its significance as human pathogen was not discovered before the 1950s. In cattle it causes mastitis

Mastitis

Mastitis is the inflammation of breast tissue. S. aureus is the most common etiological organism responsible, but S. epidermidis and streptococci are occasionally isolated as well.-Terminology:...

, an infection of the udder

Udder

An udder is an organ formed of the mammary glands of female quadruped mammals, especially ruminants such as cattle, goats, sheep and deer. The udder is a single mass hanging beneath the animal, consisting of pairs of mammary glands...

. It can either give acute, febrile disease or sub-acute, more chronic disease. Both lead to diminishing milk production (hence its name: agalactiae meaning "no milk"). Outbreaks in herds are common. This is of major significance for the dairy industry

Dairy

A dairy is a business enterprise established for the harvesting of animal milk—mostly from cows or goats, but also from buffalo, sheep, horses or camels —for human consumption. A dairy is typically located on a dedicated dairy farm or section of a multi-purpose farm that is concerned...

 and programs to reduce the impact of S.agalactiae disease have been enforced in many countries over at least the last 30-40 years.

Other animals

Fisheries and wildlife officers from Queensland, Australia, have been investigating the deaths of more than 50 grouper

Giant grouper

The giant grouper , also known as the brindle bass, brown spotted cod, or bumblebee grouper and as the Queensland groper in Australia, is the largest bony fish found in coral reefs, and the aquatic emblem of Queensland, Australia. It is found throughout the Indo-Pacific region, with the exception...

fish, between 2008 and 2010, that have washed up dead on beaches in the north of the state. The fish had been infected with S. agalactiae.

External links

• Group B Strep Support
• Prevention of Perinatal Group B Streptococcal Disease August 16, 2002 MMWR 2000;49:228-232.