3.05 Streptococcus Species
Microbiology review for the USMLE Step 1 Exam.
- Streptococcus bacteria are gram positive cocci that form linear chains
- Hemolysis refers to the ability of bacteria to break down red blood cells and is classified as alpha (partial), beta (complete), or gamma (none)
- Alpha hemolytic streptococci include viridans streptococci and Streptococcus pneumoniae
- Viridans streptococci, particularly Streptococcus mutans, are common causes of dental cavities and endocarditis, while Streptococcus pneumoniae is a common cause of pneumonia
- Beta hemolytic streptococci include Group A streptococci (Streptococcus pyogenes) and Group B streptococci (Streptococcus agalactiae)
- Group A streptococci can cause strep throat, impetigo, and cellulitis, as well as more serious infections like scarlet fever and rheumatic fever
- Group B streptococci are commonly found in the vagina and rectum, and can cause infections in newborns and pregnant women, as well as urinary tract infections and pneumonia
- Gamma hemolytic streptococci include the Enterococcus species, which can cause urinary tract infections, endocarditis, and other infections, and can be resistant to some antibiotics
- Lancefield grouping refers to the presence of different types of carbohydrate antigens on the surface of streptococcus bacteria and is used in classification and identification of streptococcus species
