Bacteria Gram-staining.

What is Gram staining?
A type of differential staining, commonly used to differentiate bacterial species into two large groups (Gram-positive and Gram-negative) based on the physical properties of their cell walls.

Gram-positive bacteria have a thick mesh-like cell wall made of peptidoglycan (50-90% of cell wall), which stains purple while Gram-negative bacteria have a thinner layer (10% of cell wall), which stains pink.

Aerobic bacteria.

Gram-positive cocci
- Staphylococci
- Streptococci
- Pneumococci

Gram-positive bacilli
- Corynebacterium
- Bacillus
- Clostridium
- Actinomycetes (filamentous)
- Mycobacterium (stains poorly)

Gram-positive coccobacilli
- Listeria
- Erysipelothrix

Gram-negative cocci
- Neisseria
- Moraxella

Gram-negative bacilli
- all aerobic bacteria which have not been mentioned.

Gram-negative coccobacilli
- Bordetella
- Brucella

Anaerobic Bacteria.

Gram-positive cocci
- Peptococcus
- Peptostreptococcus

Gram-positive bacilli
- Eubacterium
- Lactobacillus
- Bifidobacterium
- Propionibacterium
- Actinomyces
- Mobiluncus

Gram-negative cocci
- Veillonella

Gram-negative bacilli
- Bacteroides
- Prevotella
- Porphyromonas
- Fusobacterium
- Leptotrichia


tips : there are about 30 bacteria species which are Gram-negative bacilli. so in viva voce, if you unsure about the Gram staining of an aerobic bacilli, just say Gram-negative bacilli! insyaAllah, it worth a guess :)