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