Remember:

• Gram-positive cocci = staphylococci + streptococci (including enterococci)
• Gram-negative cocci = Neisseria meningitidis + Neisseria gonorrhoeae, also Moraxella catarrhalis

Therefore, only a small list of Gram-positive rods (bacilli) need to be memorised to categorise all bacteria - mnemonic = ABCD L

• Actinomyces
• Bacillus anthracis (anthrax)
• Clostridium
• Diphtheria: Corynebacterium diphtheriae
• Listeria monocytogenes

Remaining organisms are Gram-negative rods, e.g.:

• Escherichia coli
• Haemophilus influenzae
• Pseudomonas aeruginosa
• Salmonella sp.
• Shigella sp.
• Campylobacter jejuni