Streptococci
Streptococcus is often divided into alpha-haemolytic and beta haemolytic groups. Alpha haemolysis indicates partial or incomplete lysis of red blood cells, often appearing as a greenish discolouration around the bacterial colonies, while beta haemolysis means complete destruction of red blood cells, resulting in a clear zone around the colonies. Streptococci classes are shown below:
| Alpha-hemolytic | Beta-hemolytic |
|---|---|
|
Alpha-Haemolytic Streptococci
Alpha-haemolytic streptococci are a group of Gram-positive, catalase-negative cocci that cause partial haemolysis of red blood cells, producing a greenish discoloration on blood agar. The main members include:
Role in endocarditis
Viridans group streptococci (VGS) are a common cause of subacute infective endocarditis, particularly affecting damaged or prosthetic heart valves.
They are normal flora of the oral cavity, and can enter the bloodstream during dental procedures, poor oral hygiene, or mucosal trauma.
VGS are low-virulence organisms, leading to slowly progressive endocarditis characterised by nonspecific symptoms such as fatigue, low-grade fever, and weight loss.
Blood cultures typically grow the organism, and echocardiography confirms vegetations.
Amoxicillin is commonly used for prophylaxis; alternatives like clindamycin may be given in penicillin-allergic patients.
Alpha-haemolytic streptococci are a group of Gram-positive, catalase-negative cocci that cause partial haemolysis of red blood cells, producing a greenish discoloration on blood agar. The main members include:
- Streptococcus viridans group (e.g., S. mitis, S. sanguinis, S. oralis, S. mutans)
- Streptococcus pneumoniae (not part of viridans group but also alpha-haemolytic)
Role in endocarditis
Viridans group streptococci (VGS) are a common cause of subacute infective endocarditis, particularly affecting damaged or prosthetic heart valves.
They are normal flora of the oral cavity, and can enter the bloodstream during dental procedures, poor oral hygiene, or mucosal trauma.
VGS are low-virulence organisms, leading to slowly progressive endocarditis characterised by nonspecific symptoms such as fatigue, low-grade fever, and weight loss.
Blood cultures typically grow the organism, and echocardiography confirms vegetations.
Procedural prophylaxis
Antibiotic prophylaxis is recommended before certain invasive dental or surgical procedures for patients at high risk of infective endocarditis, such as:- Patients with prosthetic heart valves
- Previous history of infective endocarditis
- Congenital heart diseases
- Cardiac transplant recipients with valvulopathy
Amoxicillin is commonly used for prophylaxis; alternatives like clindamycin may be given in penicillin-allergic patients.