3.03 Gram Positive Bacteria

Microbiology review for the USMLE Step 1 Exam.

• Gram positive bacteria are characterized by their ability to retain the violet stain during the gram stain procedure, due to their thick peptidoglycan cell walls
• Gram positive bacteria can be cocci (spherical) or bacilli (rod-shaped)
• Cocci can be grouped in clusters, pairs, or chains
• Gram positive cocci in pairs or chains include streptococcus (pairs or chains), enterococcus (pairs), and staphylococcus (clusters)
• Hemolysis describes the ability of a bacteria species to break down red blood cells and is categorized as alpha (partial), beta (complete), or gamma (none)
• Coagulase activity refers to the presence of an enzyme that causes blood to coagulate and is present in some staphylococcus species
• Gram positive bacilli can be aerobic (listeria, bacillus, corynebacterium) or anaerobic (clostridium)