A pus culture on chocolate agar shows gram-negative cocci most likely organism is
**Core Concept**
The question is testing the student's ability to identify a gram-negative coccus based on its growth characteristics on chocolate agar. Chocolate agar is a type of agar medium that contains heat-treated blood, which provides an ideal growth environment for certain fastidious bacteria.
**Why the Correct Answer is Right**
Gram-negative cocci are typically seen in the genus Neisseria. The most likely organism in this case is Neisseria gonorrhoeae, which is a gram-negative diplococcus that causes gonorrhea. This organism grows well on chocolate agar due to its requirement for reduced oxygen tension and the presence of X and V factors. N. gonorrhoeae is a fastidious bacterium that requires these specialized conditions to grow. The X factor is a heat-labile component of blood that is necessary for the growth of N. gonorrhoeae, while the V factor is a heat-stable component that is also required.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a gram-negative coccus that grows well on chocolate agar. Many gram-positive cocci, such as Staphylococcus aureus, do not grow well on chocolate agar.
**Option B:** This option is incorrect because it does not specify a gram-negative coccus that grows well on chocolate agar. Many gram-negative rods, such as Escherichia coli, do not grow well on chocolate agar.
**Option C:** This option is incorrect because it does not specify a gram-negative coccus that grows well on chocolate agar. Many gram-positive cocci, such as Streptococcus pneumoniae, do not grow well on chocolate agar.
**Clinical Pearl / High-Yield Fact**
Neisseria gonorrhoeae is a sexually transmitted bacterium that can cause serious complications if left untreated, including pelvic inflammatory disease in women and epididymitis in men. It is also resistant to many antibiotics, making treatment challenging.
**Correct Answer: D. Neisseria gonorrhoeae.**