Characteristics and Clinical Relevance of Streptococcus

Because of this risk, pregnant women are routinely screened for Group B Strep colonization between 35 and 37 weeks of gestation. If the culture is positive, prophylaxis with antibiotics such as penicillin, ampicillin, or cefazolin is administered during labor to protect the newborn.

Streptococcus pneumoniae

Streptococcus pneumoniae is an alpha-hemolytic, lancet-shaped Gram-positive coccus. Its primary virulence factor is a polysaccharide capsule, which prevents phagocytosis by the host immune system. This capsule is so central to the bacteria's survival that it serves as the basis for many modern vaccines.

Clinically, S. pneumoniae is a leading cause of several respiratory and systemic infections:

• Lobar pneumonia: The most common cause of community-acquired bacterial pneumonia.
• Otitis media: A frequent cause of ear infections in children.
• Meningitis: The most common cause of bacterial meningitis in adults.
• Sinusitis: A common cause of acute bacterial sinus infections.

Patients who are asplenic (due to splenectomy or sickle cell anemia) are at a significantly higher risk for sepsis caused by S. pneumoniae.

Viridans Group Strep

The Viridans group consists of several similar species that do not belong to the major Lancefield groups (A, B, or D). They are part of the normal oral flora and are associated with two distinct clinical scenarios:

1. Dental Caries: Streptococcus mutans is a key player in the development of tooth decay.
2. Subacute Endocarditis: Streptococcus sanguis can cause a slow-onset infection of the heart valves. This typically occurs in patients with pre-existing valve abnormalities, often following dental procedures that allow the bacteria to enter the bloodstream. Unlike the acute endocarditis caused by Staphylococcus aureus, Viridans-induced endocarditis presents with a slower onset and the patient often appears less acutely ill.

Enterococcus

Enterococcus species (such as E. faecalis and E. faecium) are Lancefield Group D organisms and are normal inhabitants of the colon. They are known for their relative resistance to many cell-wall-acting antibiotics, including penicillin and ampicillin.

A major clinical concern is Vancomycin-resistant enterococci (VRE), which are dangerous hospital-acquired infections. Enterococci are also common causes of urinary tract infections (UTIs), particularly in hospital settings associated with catheter use. While most UTIs are caused by E. coli, Enterococcus is a significant secondary cause.

Clinical Note: In cases of Enterococcus UTIs associated with catheters, the removal of the catheter alone may sometimes be sufficient to cure the infection.