Streptococcus and Enterococcus Overview

Greek origin of "Streptus" means easily bent or twisted, reflecting the bacterial arrangement.
Classified under families Streptococcaceae (Streptococcus) and Enterococcaceae (Enterococcus).
Classification is based on serological (Lancefield) typing, hemolysis patterns on blood agar (BA), and biochemical tests.

Both genera consist of Gram-positive cocci, often found in pairs or chains consisting of 3-30 cells.
Size ranges from 0.5 to 2 µm and are facultative anaerobes; some can thrive in elevated CO2 conditions.
Growth requires enriched media, with exceptions for non-fastidious Enterococcus, and optimal incubation temperature at 35-37°C.
Hemolysis can be α (partial), β (complete), or γ (non-hemolytic), with colonies exhibiting varying morphology.
All species are catalase negative, fermentative, non-spore forming, and non-motile.

Most common infections are caused by Group A (S. pyogenes), Group B (S. agalactiae), and Group C streptococci.
Rare infections involve Groups E, F, G, and L, which contain diverse streptococcal species.
Group D encompasses the Enterococcus genus, previously categorized under Streptococcus.

β-hemolytic streptococci appear as Gram-positive cocci in chains, 1-2 µm in diameter, capable of producing β-hemolytic colonies on blood agar.
Yield white, convex colonies sizes between ≤1-2 mm; typically catalase negative.
Bacitracin susceptibility varies, with some being resistant.
Pyrrolidonyl arylamidase (PYR) test results are variable across Lancefield groups.

Group A: S. pyogenes (large colonies), Anginosus group (small colonies).
Group B: S. agalactiae (large colonies).
Group C: S. dysgalactiae subsp. equisimilis (both large and small colonies), Anginosus group.
Group F: Anginosus group (small colonies).
Group G: S. dysgalactiae subsp. equisimilis (large), Anginosus group (small colonies).
Nongroupable species: frequently small colonies from the Anginosus group.

Early onset of Streptococcus infections can present as respiratory distress, fever, lethargy, and hypotension in neonates.
Late-onset infections may occur 7 days to 3 months post-birth.
Group C and G streptococci can cause pharyngitis and are common bacterial pneumonia agents in children under 5 years and individuals over 50 or with weakened defenses.
Clinical pneumonia characteristics include sudden onset, chills, high fever, coughing (pink to rusty sputum), and pleuritic chest pain.

The 13-valent conjugated pneumococcal vaccine is recommended for infants under 2 years and administered in four doses.
Vaccine efficacy is influenced by prevalent serotypes causing invasive disease and is less effective in patients with specific underlying health conditions (asplenia, sickle cell disease, etc.).