You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Which of the following is gram-positive bacillus- and explain in detail?
Listeria is gram-positive bacillus.
Staphylococcus and streptococcus are also gram-positive, but they are cocci (not bacilli).
Meningococci are gram-negative cocci.

Also know

Clinically important spore-forming bacteria are gram-positive → Clostridium, Bacillus.
Listeria is the only gram-positive bacteria that has endotoxin. (Endotoxin is present only in gram-negative organisms).
Of the gram-negative organisms, only two groups are cocci - Neisseria (meningococcus & gonococcus), veillonella.
All other gram-negative organisms are bacilli (including coccobacilli).
Amongst medically important bacilli '6' are gram (+)ve → Actinomycetes, clostridium, mycobacteria, Bacillus, Listeria, Corynebacterium.
All other medically important bacilli are gram-negative.