Identifying gram-positive bacteria
Gram positive bacteria will turn purple/blue following the gram staining. Microscopy will then reveal the shape, either cocci or rods.
Rods (bacilli)
Cocci
Staphylococci
Streptococci
α-haemolytic streptococci
β-haemolytic streptococci
 | |
Rods (bacilli)
- Actinomyces
- Bacillus antracis
- Clostridium
- Corynebacterium diphtheriae
- Listeria monocytogenes
Cocci
- makes catalase: Staphylococci
- does not make catalase: Streptococci
Staphylococci
- makes coagulase: S. aureus
- does not make coagulase: S. epidermidis (novobiocin sensitive), S. saprophyticus (novobiocin resistant)
Streptococci
- partial haemolysis (green colour on blood agar): α-haemolytic
- complete haemolysis (clear): β-haemolytic
- no haemolysis: γ-haemolytic
α-haemolytic streptococci
- optochin sensitive: S. pneumoniae
- optochin resistant: Viridans streptococci
β-haemolytic streptococci
- bacitracin sensitive: Group A: S. pyogenes
- bacitracin resistant: Group B: S. agalactiae