Streptococcus pyogenes = Lancefield Group A

Taxonomy
Family: Streptococcaceae

Natural habitats
Colonizes the human throat and skin and has developed complex virulence mechanism to avoid host defenses.

Clinical significance
The upper respiratory tract and skin lesions serve as primary focal sites of infections and principal reservoirs of transmission.

They can cause superficial or deep infections due to toxin-mediated and immunologically mediated mechanisms of disease.

S. pyogenes is the most common cause of bacterial pharyngitis and impetigo.

In the past, S. pyogenes was a common cause of childbed fever of puerperal sepsis.

They are responsible for deep or invasive infections, especially bacteremia, sepsis, deep soft tissue infections, such as erysipelas, cellulitis, and necrotizing fasciitis.

Less common myositis, osteomyelitis, septic arthritis, pneumonia, meningitis, endocarditis, pericarditis, and severe neonatal infections following intrapartum transmission.

Taxonomy
Family: Streptococcaceae

Streptococcus dysgalactiae ssp equisimilis = Lancefield Group A, C, G or L

Natural habitats
Are normal commensal flora of the human upper airway and frequently are asymptomatic colonizers of the skin, gastrointestinal tract and female genital tract.

Clinical significance
After being considered nonpathogenic for many years, they are now recognized as an important bacterial pathogen.

The clinical spectrum of diseases caused by this species closely resembles Streptococcus pyogenes infections.

S. dysgalactiae ssp equisimilis and S.pyogenes share virulence factors.
The M protein is an important virulence factor because it confers resistance to phagocytosis

They are also implicated in mono- and polymicrobial infections of the skin and soft tissues, pharyngitis, bacteremia and endocarditis, septic arthritis and osteomyelitis, puerperal infections, and meningitis.

Streptococcus agalactiae = Lancefield Group B

Taxonomy
Family: Streptococcaceae

Natural habitats
Isolated from human urogenital tract and intestine

Clinical significance
They are the cause of invasive neonatal infections.

Neonatal infections present as two different clinical entities
- early onset neonatal disease, characterized by sepsis and pneumonia within the first 7 days of life
- late onset disease with meningitis and sepsis between 7 days and 3 month of age.

The most important risk factor for the development of invasive neonatal disease is the colonization, urogenital by S.agalactiae, which is found by pregnant women

Infections of adult patients may be observed as postpartum infections or in immunocompromised adult patients with alcoholism, diabetes mellitus, cancer or AID’s.

The spectrum of infections in adult patients includes pneumonia, bacteremia, endocarditis, urinary tract infections, skin and soft tissue infections and osteomyelitis