Neisseria meningitidis

Neisseria meningitidis, also called N. meningitidis or just meningococcus, is a gram-negative round bacterium that causes meningitis in humans, as well as life-threatening conditions like sepsis and disseminated intravascular coagulation.

Now, N. meningitidis has a thin peptidoglycan layer, so it doesn’t retain the crystal violet dye during Gram staining.

Instead, like any other Gram-negative bacteria, it stains pink with safranin dye.

N. meningitidis typically live in pairs called diplococci, stacked side to side, so the pair looks like a coffee bean.

They are also non-motile, non-spore forming, and obligate aerobes, which means that they absolutely need oxygen to grow.

Finally, they’re catalase and oxidase positive - which means they produce both these enzymes.

N. meningitidis grows on a special chocolate medium called Thayer-Martin agar, which mainly consists of sheep’s blood... err, yum?

Some antimicrobials, like vancomycin and nystatin are usually added to the Thayer-Martin agar, to inhibit the possible growth of undesired bacteria or fungi, and maximize the growth of Neisseria species.

However, other Neisseria species, like N gonorrhoeae, also share these properties.

So the maltose fermentation test is done to differentiate the two.

The gist of it is that N. meningitidis can ferment maltose, whereas N. gonorrhoeae cannot.

To check for this, a pure sample from the culture is transferred to a sterile tube containing a mix of phenol red and maltose, which is then incubated at 36 degrees Celsius for 24 hours.

N. meningitidis causes acidic fermentation of maltose, and the resulting byproducts make the solution go yellow.

With N. gonorrhoeae, the solution stays red.

Now, N. meningitidis has a number of virulence factors, that are like assault weaponry that help it attack and destroy the host cells, and evade the immune system.