This bacteria is characterized by the presence of group B Lancefield antigen and commonly called group B Streptococci (GBS).
This organism stains positive on Gram stain due to thick peptidoglycan layer which absorbs crystal violet.
This bacterium has a spherical shape.
Strep agalactiae typically produces large zones of beta-hemolysis, which is complete lysis of red cells in the blood culture media.
Bacitracin can be used to distinguish Strep agalactiae from other beta-hemolytic Streptococci, like Strep pyogenes. Streptococcus pyogenes is bacitracin- sensitive, while Streptococcus agalactiae is bacitracin-resistant.
Characteristically, Streptococcus agalactiae is catalase-negative, meaning it does not produce the enzyme catalase. This enzyme allows bacterium to convert hydrogen peroxide to water and oxygen. This characteristic is helpful in distinguishing Streptococci from catalase-positive Staphylococci.
Streptococcus agalactiae does not have activity of the enzyme pyrrolidonyl arylamidase. Thus, it produces a negative test, resulting in an orange or yellow color of the reagent. Streptococcus agalactiae is known to be pyrrolidonyl arylamidase- negative, and serves as a negative control in this test.
An important virulence factor of this organism is its capsule, composed of polysaccharides. These bacterial capsules completely surround bacterial cell, and enhance the ability of bacteria to cause disease.
The hippurate hydrolysis test is used to detect the ability of bacteria to hydrolyse hippurate into glycine and benzoic acid, and serves as a presumptive identification test for Gardnerella vaginalis, Campylobacter jejuni, Listeria monocytogenes and group B streptococci.
A CAMP test is frequently used to identify group B streptococci based on their formation of CAMP factor, which causes the area of hemolysis formed by beta-hemolysin from Staphylococcus aureus to be enlarged.
A CAMP test is frequently used to identify Group B streptococci based on their formation of CAMP factor, which causes the area of hemolysis formed by beta hemolysin from Staphylococcus aureus to be enlarged.
S. agalactiae is commonly transferred to neonates during passage through the birth canal, and can cause serious infections in infants including pneumonia, meningitis, and sepsis.
GBS infection of newborns can cause inflammation of the meninges. However, S. agalactiae neonatal meningitis typically does not present with the characteristic sign of stiff neck. Instead, infants typically present with nonspecific symptoms of fever, vomiting and irritability. Hearing loss can be a long-term sequela.
This organism can invade alveolar and pulmonary epithelial cells of infants when inhaled during vaginal delivery. Newborns are especially susceptible to infection due to lack of alveolar macrophages.
This organism is a major cause of bacterial sepsis of newborns. Early onset sepsis is typically accompanied by pneumonia, while onset after seven days is more often accompanied by meningitis.
S. agalactiae is a member of the GI normal flora in some people and can spread to secondary sites including the vagina in approximately 20% of women. Colonization of the vagina is important clinically because it can be transferred to neonates during passage through the birth canal and cause serious infections.
Pregnant women are routinely screened for the presence of S. agalactiae (GBS) in the vagina at 35-37 weeks. Women with positive cultures can receive intrapartum prophylactic treatment with IV penicillin during delivery.
Women with positive cultures can receive intrapartum prophylactic treatment with IV penicillin during delivery.
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