Streptococcus
Classification and Characteristics
Streptococcus is a genus of Gram-positive bacteria that are spherical in shape and typically appear in chains. They belong to the phylum Firmicutes and the class Bacilli. Streptococci are classified into several groups based on their hemolytic properties, serological reactions, and other characteristics.
Hemolytic Classification
Streptococci are classified into three groups based on their hemolytic properties: alpha (α), beta (β), and gamma (γ) hemolytic. Alpha-hemolytic streptococci cause partial hemolysis of red blood cells, producing a green coloration on blood agar. This group includes Streptococcus pneumoniae and a group of streptococci known as viridans streptococci. Beta-hemolytic streptococci cause complete hemolysis, producing a clear zone on blood agar. This group includes Streptococcus pyogenes, Streptococcus agalactiae, and others. Gamma-hemolytic streptococci do not cause hemolysis.
Serological Classification
The Lancefield grouping, named after Rebecca Lancefield, is a method of grouping catalase-negative, coagulase-negative bacteria based on the carbohydrate composition of bacterial antigens found on their cell walls. Streptococci are classified into several groups (A to V) based on this method. For example, Streptococcus pyogenes belongs to group A, while Streptococcus agalactiae belongs to group B.
Pathogenicity and Diseases
Streptococci are responsible for a wide range of diseases in humans and animals. Streptococcus pneumoniae is a leading cause of pneumonia, meningitis, and otitis media in humans. Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes diseases ranging from mild skin infections and pharyngitis (strep throat) to severe diseases such as necrotizing fasciitis (flesh-eating disease) and streptococcal toxic shock syndrome. Streptococcus agalactiae, or group B Streptococcus (GBS), is a common cause of neonatal sepsis and meningitis.
Treatment and Prevention
Treatment of streptococcal infections typically involves antibiotics. Penicillin and amoxicillin are commonly used for treatment, although resistance to these antibiotics has been reported in some streptococcal species. Vaccines are available for some types of streptococci, such as Streptococcus pneumoniae. Prevention of streptococcal infections often involves good hygiene practices, such as hand washing.