A 70 year old man presents with complaints of chest pain, fever, cough with sputum. On examination of sputum pus cells with gram positive cocci are present. Blood agar showed positive result. How will you differentiate this from other gram positive cocci?
## **Core Concept**
The patient's presentation suggests pneumonia, and the presence of gram-positive cocci in the sputum along with a positive result on blood agar points towards a bacterial infection. The likely pathogen could be *Streptococcus pneumoniae*, given the clinical context and laboratory findings.
## **Why the Correct Answer is Right**
To differentiate *Streptococcus pneumoniae* from other gram-positive cocci, such as *Streptococcus pyogenes* or *Staphylococcus aureus*, specific tests are employed. *S. pneumoniae* is known for its sensitivity to optochin (ethylhydrocupreine hydrochloride). The optochin sensitivity test is a rapid and reliable method for identifying *S. pneumoniae*; the bacteria are sensitive to optochin, which inhibits their growth. This characteristic is crucial for differentiation.
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option might suggest another method of identification, but without specifics, it's hard to directly refute. However, given that optochin sensitivity is a well-established method for *S. pneumoniae*, alternatives might not be as straightforward or specific.
- **Option B:** This could potentially refer to another test, but like Option A, without specifics, it's challenging to directly address. The key here is that the correct method involves optochin sensitivity.
- **Option C:** If this option suggests a method that is not specific or sensitive for *S. pneumoniae*, it would be incorrect. For instance, bile solubility is another test used for *S. pneumoniae*, but it's not as rapid or commonly used for initial differentiation as the optochin test.
## **Clinical Pearl / High-Yield Fact**
A critical clinical pearl is that *Streptococcus pneumoniae* is a common cause of community-acquired pneumonia, especially in elderly patients, and its identification is key for targeted antibiotic therapy. The optochin sensitivity test is a valuable tool in the rapid identification of *S. pneumoniae* from clinical specimens.
## **Correct Answer:** D. Optochin sensitivity.