Neisseria gonorrhoeae

Neisseria gonorrhoeae, also known as N. gonorrhoeae to its friends, is a gram-negative oval bacterium that infects humans, causing a number of infections including gonorrhea.

The word Neisseria came from Neisser Albert, a German physician who discovered it, while gonorrhea is from the Greek words “gonos” which means "seed", and “rhoe” which means "flow", meaning "flow of seed", an illustration referring to the penile purulent discharge, which was mistakenly thought to be semen in infected males.

Now, a little bit of microbe anatomy and physiology. N. gonorrhoeae is a gram-negative bacterium, because its cell wall has a thin peptidoglycan layer and so it doesn’t retain purple dye used during Gram staining.

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

N. gonorrhoeae 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. gonorrhoeae grows on a special chocolate medium called Thayer-Martin agar, which mainly consists of sheep 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. meningitidis, have the same properties.

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

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

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

Since N. gonorrhoeae can’t ferment maltose, the solution stays red, whereas with N. meningitidis, fermentation byproducts make the solution go yellow.

Now, unlike its sister Neisseria meningitidis, Neisseria gonorrhoeae is not an encapsulated bacteria, so it doesn’t have a polysaccharide capsule.

But this bacteria has a ton of other virulence factors, which it uses to attack and destroy host cells, and also to evade the immune system.