A 33-year-old woman begins seeing a new boyfriend. Several weeks later, a week after her menstrual period, the woman develops a painful, swollen right knee. The most likely causative organism has which of the following characteristics?
**Core Concept**
The question is testing the student's knowledge of gonococcal arthritis, a type of septic arthritis caused by the bacterium *Neisseria gonorrhoeae*. This infection typically presents as a monoarticular arthritis, often in the knee, and is associated with a characteristic gonococcal infection, usually sexually transmitted.
**Why the Correct Answer is Right**
*Neisseria gonorrhoeae* is a gram-negative diplococcus that is highly infectious and can cause a range of symptoms, from urethritis to disseminated gonococcal infection (DGI). In DGI, the bacteria can cause a migratory polyarthritis, characterized by inflammation of multiple joints, often accompanied by a rash. The presentation of gonococcal arthritis in this patient, a week after her menstrual period, suggests that the infection was likely acquired during sexual activity.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because *Staphylococcus aureus* is a gram-positive cocci that is a common cause of skin and soft tissue infections, but it is not typically associated with the type of presentation described in the question.
**Option B:** This option is incorrect because *Klebsiella pneumoniae* is a gram-negative bacillus that can cause a range of infections, including urinary tract infections and pneumonia, but it is not typically associated with gonococcal arthritis.
**Option C:** This option is incorrect because *Escherichia coli* is a gram-negative bacillus that is a common cause of urinary tract infections and other types of infections, but it is not typically associated with gonococcal arthritis.
**Clinical Pearl / High-Yield Fact**
When considering the diagnosis of gonococcal arthritis, remember that it often presents as a monoarticular arthritis in the knee, and is associated with a characteristic gonococcal infection, usually sexually transmitted.
**Correct Answer:** C. *Neisseria gonorrhoeae* is a gram-negative diplococcus that is highly infectious and can cause a range of symptoms, from urethritis to disseminated gonococcal infection (DGI).