A 34-year-old pregnant female presented to the ER with fever, backache, headache and myalgias. Blood cultures were collected and subjected to examination. Microbiological examination revealed positive motility at 25 degree Celsius and catalase positivity, Esculin positivity and positive growth in 6.5% NaCl. The colonies are as shown on blood agar plate given below. Gram Staining Which of the following is the most common route of transmission of the above organism: –

## **Core Concept**
The question describes a clinical scenario with a pregnant female presenting with symptoms suggestive of a systemic infection. The microbiological characteristics provided, such as positive motility at 25°C, catalase positivity, esculin positivity, and growth in 6.5% NaCl, are key to identifying the organism. These features are typical of *Listeria monocytogenes*, a Gram-positive rod.

## **Why the Correct Answer is Right**
The organism in question exhibits characteristics highly suggestive of *Listeria monocytogenes*:
- **Positive motility at 25°C**: *L. monocytogenes* shows characteristic tumbling motility at room temperature (25°C).
- **Catalase positivity**: This indicates the organism's ability to produce catalase, an enzyme that decomposes hydrogen peroxide.
- **Esculin positivity**: *L. monocytogenes* is esculin positive, which helps in its identification.
- **Growth in 6.5% NaCl**: This is another feature of *L. monocytogenes*, indicating its ability to grow in high salt concentrations.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although not specified, common routes of transmission for many pathogens do not apply here given the organism's identification.
- **Option B:** This option might suggest a route not typically associated with *L. monocytogenes* transmission.
- **Option C:** This could imply a route not primarily linked with the organism in question.

## **Clinical Pearl / High-Yield Fact**
A critical point to remember is that *Listeria monocytogenes* is commonly transmitted through **contaminated food**, particularly soft cheeses, hot dogs, and deli meats. Pregnant women are at increased risk of listeriosis, which can lead to severe outcomes such as miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.

## **Correct Answer:** . **C. Food**

✓ Correct Answer: C. Ingestion of contaminated food