Streptococcus agalactiae- An Overview


Streptococcus agalactiae (also known as group B streptococcus or GBS) is a gram-positive coccus (round bacterium) that belongs to the genus Streptococcus. It is a beta-hemolytic, catalase-negative, and facultative anaerobe that can grow in the presence or absence of oxygen. It is the only member of the Lancefield group B of streptococci, which are classified based on their cell wall carbohydrate antigens. It has ten different serotypes (Ia, Ib, II-IX) that are distinguished by their capsular polysaccharide structures.

S. agalactiae is a part of the normal flora of the human gastrointestinal and genitourinary tracts, where it usually does not cause any harm. However, it can also be a pathogen that causes serious infections in neonates, pregnant women, older adults, and immunocompromised individuals. It is the leading cause of neonatal sepsis and meningitis, and can also cause pneumonia, endocarditis, osteomyelitis, arthritis, skin and soft tissue infections, and urinary tract infections.

S. agalactiae was first recognized as a cause of bovine mastitis (inflammation of the udder) by Edmond Nocard in 1887. The species name `agalactiae` means `want of milk` in Greek, reflecting its effect on milk production in cows. It was later found to be a human pathogen by Rebecca Lancefield in the 1930s after she isolated it from the blood of women with postpartum sepsis. Since then, S. agalactiae has emerged as a major public health concern due to its high morbidity and mortality rates in vulnerable populations.

The prevention and treatment of S. agalactiae infections depend on the identification and characterization of the organism by various laboratory methods. These include morphological, cultural, biochemical, immunological, and molecular tests that can detect and differentiate S. agalactiae from other streptococci and bacteria. The use of intrapartum antibiotic prophylaxis for colonized pregnant women has reduced the incidence of early-onset neonatal disease significantly. However, late-onset neonatal disease and adult infections remain challenging to prevent and manage. Therefore, there is a need for developing effective vaccines and novel therapies against S. agalactiae infections.

In this article, we will provide an overview of S. agalactiae, covering its classification, habitat, morphology, cultural characteristics, biochemical characteristics, virulence factors, pathogenesis, clinical manifestations, laboratory diagnosis, treatment, and prevention.