A 4 yr old partially immunized boy came to OPD with history of bouts of coughing. On staining the sputum sample an organism with bipolar staining was seen. Which among the following organism it would be?
**Core Concept**
Bipolar staining is a characteristic feature of certain bacteria that exhibit a "safety pin" or "kidney bean" appearance under the microscope. This phenomenon occurs due to the presence of a thick capsule and the partial decolorization of the cell wall, resulting in a distinctive appearance.
**Why the Correct Answer is Right**
_Bordetella pertussis_, the causative agent of pertussis or whooping cough, exhibits bipolar staining due to the presence of a thick capsule and the partial decolorization of the cell wall. This unique staining pattern is a key diagnostic feature of _B. pertussis_. The organism's ability to adhere to the respiratory epithelium and produce toxins, including the pertussis toxin, contributes to its pathogenicity.
**Why Each Wrong Option is Incorrect**
**Option A:** *Yersinia pestis*, the causative agent of plague, typically exhibits bipolar staining, but it is not associated with coughing bouts in a 4-year-old child.
**Option C:** *Streptococcus agalactiae*, a group B streptococcus, does not exhibit bipolar staining and is not typically associated with pertussis-like symptoms.
**Option D:** *Klebsiella pneumoniae*, a gram-negative rod, does not exhibit bipolar staining and is not typically associated with pertussis-like symptoms.
**Clinical Pearl / High-Yield Fact**
Pertussis is a highly contagious respiratory illness that can spread even among immunized individuals, highlighting the importance of maintaining herd immunity through vaccination.
✓ Correct Answer: B. B. pertussis