A child comes to an emergency room because of an infected dog bite. The wound is found to contain small Gram-negative rods. The most likely cause of infection is
**Core Concept**
The question is testing the student's knowledge of the common pathogens responsible for animal bite infections. The underlying principle is the identification of the causative agent based on Gram staining characteristics. In this case, the presence of small Gram-negative rods suggests a specific bacterial species.
**Why the Correct Answer is Right**
The presence of small Gram-negative rods in the wound suggests that the causative agent is *Pasteurella multocida*. This bacterium is commonly found in the oral flora of dogs and is often associated with animal bites. *Pasteurella multocida* can cause a range of infections, from mild cellulitis to severe systemic infections. The bacterium's small size and Gram-negative staining characteristics make it a prime suspect in this scenario.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely to be incorrect because the description does not match any common Gram-negative rods associated with animal bites. A more likely candidate would be *Pasteurella multocida*.
* **Option B:** This option is incorrect because *Streptococcus pyogenes* is a Gram-positive bacterium, not a Gram-negative rod. While it can cause infections, it is not the most likely cause in this scenario.
* **Option C:** This option is incorrect because *Escherichia coli* is a Gram-negative rod, but it is not typically associated with animal bites. It is more commonly found in the gastrointestinal tract and is often a cause of urinary tract infections.
* **Option D:** This option is incorrect because *Klebsiella pneumoniae* is a Gram-negative rod, but it is not typically associated with animal bites. It is more commonly found in the respiratory tract and is often a cause of pneumonia.
**Clinical Pearl / High-Yield Fact**
When evaluating a patient with an animal bite infection, it is essential to consider the type of animal involved and the wound's location. In this case, the presence of small Gram-negative rods in a dog bite wound suggests *Pasteurella multocida* as the most likely causative agent.
**Correct Answer:** C. *Pasteurella multocida*