Neisseria gonorrhoeae

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Neisseria gonorrhoeae

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USMLE® Step 1 style questions USMLE

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A 22-year-old woman presents to the primary care clinic due to painful urination. Her symptoms began three days ago and have progressed to bothering the patient throughout the day. The patient also developed foul-smelling vaginal discharge over the last two days. A Gram stain of a cervical swab is obtained and shown in the figure below. Which of the following characteristics is true regarding the causative pathogen of this patient’s condition?  

External References

First Aid

2024

2023

2022

2021

Arthritis p. 472

gonococcal p. 474

Ceftriaxone

for gonococci p. 140

Conjunctivitis p. 549

gonococcal prophylaxis p. 194

gonococci p. 140

Gonococci vs meningococci p. 140

Gonorrhea

gonococci p. 140

Neisseria gonorrhoeae p. , 140

culture requirements p. 124

Gram-negative algorithm p. 139

osteomyelitis p. 177

septic arthritis p. 474

STI p. 182

UTIs with p. 619

Pelvic inflammatory disease (PID) p. 182

gonococci p. 140

Polyarthralgias

gonococcal arthritis p. 474

Septic arthritis p. 474

gonococci p. 140

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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.

Summary

Neisseria gonorrhoeae is a gram-negative diplococcus, non-spore-forming, both oxidase and catalase-positive bacteria, which is known to cause a sexually transmitted infection (STI) called gonorrhea.

Gonorrhea manifests as urethritis in males and vaginitis and cervicitis in females, and if left untreated, it can progress to gonococcemia, and cause complications like gonococcal sepsis, septic arthritis, and endocarditis. Gonorrhea is diagnosed through a laboratory test of a vaginal or urethral swab, and is treated with antibiotics.

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