Introduction:
Group B streptococcus (GBS) is a pathogen represented as Streptococcus agalactia. It is called group B streptococcus or GBS due to Lancefield grouping that considers specific cell wall carbohydrate antigens. It is commonly found in the gastrointestinal and genital tract. GBS colonization in pregnant women is a significant risk factor for neonatal and infant infection.
What Are the Characteristics of Group B Streptococcus?
Characteristics of GBS:
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GBS is a gram-positive, catalase-negative organism that appears as cocci in pairs and chains on gram stain.
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On blood agar, they grow as small colorless colonies that cause beta-hemolysis or complete hemolysis.
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Group B-specific cell-wall carbohydrate antigen is common for all strains of GBS.
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The capsular polysaccharide surface allows the classification of GBS into types Ia, Ib, II, III, IV, V, VI, VII, VIII, and IX.
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A surface protein antigen, C protein with alpha and beta components, is common to all strains.
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Another surface component called pilus facilitates the attachment to mucosal surfaces.
What Is the Virulence of Group B Streptococcus?
Virulence factors of GBS:
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The GBS is encapsulated by a polysaccharide layer that is rich in sialic acid, which is a substance found in humans. Thus, the inexperienced immune cells in newborns confuse the GBS for self-cells, permitting them to live inside the body.
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The pili on the capsule, which are a hair-like structure, attach to host cells.
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The GBS causes beta-hemolysin, a pore-forming toxin that destroys the host’s red blood cells resulting in hemolysis.
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GBS produces several bacterial products. Most strains possess C5a-ase, an enzyme of the serine esterase class that inactivates complement component C5a, a potent chemoattractant for neutrophils.
What Are the Types of Infections Caused by Group B Streptococcus?
The types of infections are
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Bacteremia: It refers to bacteria in the blood. Asymptomatic bacteremia normally occurs in daily activities such as oral hygiene and minor surgical or medical procedures. Whenever the immune system fails, bacteremia becomes a bloodstream infection that evolves into various clinical spectrums and is differentiated as septicemia. If left untreated and clinically significant, the bacteremia progresses to systemic inflammatory response syndrome, sepsis, septic shock, and multiple organ dysfunction syndrome.
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Sepsis: It is the body’s extreme response to an infection and is a life-threatening medical emergency. It can occur at any age and result from any infection, including covid-19. Infections leading to sepsis begin in the lungs, skin, urinary tract, or gastrointestinal tract. Long-term sepsis can result in tissue damage, organ failure, and death.
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Bone and Joint Infections: Bone infections caused by bacteria or fungi are referred to as osteomyelitis that results in painful swelling of bone marrow and soft tissue of bone. If it is not treated on time, it can cut off the blood supply and cause bone death.
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Meningitis: Meningitis is the inflammation of protective membranes covering the brain and spinal cord. A bacterial infection of the fluid causes swelling of the surrounding tissues. Bacterial meningitis can be life-threatening and requires immediate medical care. Vaccines are available to prevent bacterial meningitis.
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Pneumonia: Pneumonia is an infection of the lungs. This infection causes the air sacs and alveoli of the lungs to be filled with fluid or pus. Symptoms range from mild to severe and include cough with or without mucus, fever, chills, and difficulty in breathing.
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Urinary Tract Infections: UTIs are common infections that occur when bacteria from the skin or rectum enter the urethra and infect the urinary tract. It affects the parts of the urinary tract and, commonly, the bladder.
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Skin And Soft Tissue Infections: Usually appear as bumps on the skin resulting in redness and swelling of the affected area that can be filled with pus.
What Are the Signs and Symptoms of Group B Streptococcus Infections?
Symptoms of GBS infections:
Newborns:
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Fever.
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Difficulty feeding.
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Irritability or lethargy.
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Difficulty breathing.
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Blue-ish skin color.
Pregnant Women:
Some women test positive for GBS but do not have any symptoms.
Other Common Symptoms: (Adults)
Bacteremia:
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Fever.
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Chills.
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Low alertness.
Pneumonia:
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Fever.
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Chills.
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Cough.
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Rapid breathing or shortness of breath.
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Chest pain.
Skin and Soft Tissue Infection:
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Redness.
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Pain or swelling in the infected area.
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Warm to the touch.
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Pus or other drainages.
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Fever.
Bone and Joint Infections:
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Pain in the affected area.
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Fever.
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Chills.
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Swelling.
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Stiffness or inability to use affected limb or joint.
What Are the Risk Factors for Group B Streptococcus Infection?
The risk factors for GBS infection are:
Newborns:
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Testing positive for GBS bacteria late in pregnancy.
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Developing fever during labor.
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When their water breaks or the baby is born, having 18 hours or more pass can increase the risk of developing GBS infections.
Adults:
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Diabetes.
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Heart disease.
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Cancer or history of cancer.
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Obesity.
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Older age groups.
What Is the Diagnosis of Group B Streptococcal Infections?
Diagnosis of GBS infections includes
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History and physical examination.
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Laboratory tests: a collection of body fluids such as blood and spinal fluid for bacterial culture. In the case of UTI (urinary tract infection), urine samples are used for diagnosis.
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Imaging tests: chest X-ray to determine GBS disease.
What Is the Treatment for Group B Streptococcal Infection?
Empiric Treatment:
For sepsis, the initial therapy is Ampicillin and an Aminoglycoside- Gentamicin, effective against GBS in neonatal sepsis. Penicillin G is used for complete therapy.
Specific Treatment:
Infants with meningitis should take up a lumbar puncture one to two days into therapy to document CSF sterility. If the CSF culture is negative, Penicillin is used for therapy for 14 days, and if the CSF culture is positive, then treatment is prolonged.
Infants with bacteremia must receive a ten-day course of IV antibiotics.
The treatment course includes
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Meningitis (initial empirical therapy) - Ampicillin +Gentamicin – until cerebrospinal fluid is sterile
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Sepsis (initial empirical therapy) - Ampicillin +Gentamicin.-- until the bloodstream is sterile.
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Meningitis - Penicillin G – for 14 days.
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Bacteremia - Penicillin G - 10 days.
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Arthritis - Penicillin G - two to three weeks.
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Osteomyelitis - Penicillin G - three to four weeks.
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Endocarditis - Penicillin G - four weeks.
What Are the Preventive Measures for GBS Infections?
The preventive measures for GBS infections:
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Antibiotic prophylaxis for all mothers with a positive GBS screening culture is routinely taken at 35 to 37 weeks gestation.
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Intrapartum antibiotic prophylaxis is indicated for pregnant women in unknown GBS status if- preterm delivery is less than 37 Weeks gestation, - membrane rupture for 18 hours or more, - intrapartum temperature of 100.4 F or high, - intrapartum nucleic acid amplification test is positive.
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Prophylaxis with penicillin or beta-lactam antibiotics four hours before delivery prevents the early onset of the disease.
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Women allergic to penicillin's should receive Cefazolin. A susceptibility test should be performed for penicillin allergy, and Clindamycin or Vancomycin are used based on susceptibility patterns of isolated GBS organisms.
What Is the Differential Diagnosis of GBS Infection?
The differential diagnosis includes
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Enterobacteriaceae.
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Listeria.
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Transient tachypnea of the newborn.
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Meconium aspiration.
Conclusion:
Group B streptococcal infections cause serious medical conditions and can affect any age group, including children. The infections caused by GBS are sepsis, bacteremia, meningitis, skin and soft tissue infection, pneumonia, and bone or joint infections. These infections are diagnosed based on blood cultures and treated using antibiotics. Prevention of infections is through intrapartum antibiotic therapy among susceptible pregnant women.
