A 32-year-old female prostitute is seen at the public health clinic with fever, night sweats, and reports coughing up blood. Her medical history reveals that she is HIV positive and has lost 20 lbs over the past month. Acid-fast bacilli are observed in the sputum. After digestion of the sputum, isolation of the suspected organism is best accomplished by using which one of the following media?
A 32-year-old female prostitute is seen at the public health clinic with fever, night sweats, and reports coughing up blood. Her medical history reveals that she is HIV positive and has lost 20 lbs over the past month. Acid-fast bacilli are observed in the sputum. After digestion of the sputum, isolation of the suspected organism is best accomplished by using which one of the following media?
💡 Explanation
## **Core Concept**
The patient presents with symptoms suggestive of tuberculosis (TB), such as fever, night sweats, coughing up blood (hemoptysis), significant weight loss, and a history of HIV positivity, which increases her susceptibility to opportunistic infections like TB. The presence of acid-fast bacilli in the sputum is a diagnostic clue for TB. The organism responsible is *Mycobacterium tuberculosis*.
## **Why the Correct Answer is Right**
The correct medium for isolation of *Mycobacterium tuberculosis* after digestion of the sputum is **Lowenstein-Jensen medium**. This medium is specifically designed for the isolation and cultivation of mycobacteria. It contains ingredients that support the growth of *M. tuberculosis*, such as malachite green, which inhibits the growth of other bacteria, and glycerol, which serves as a carbon source for the mycobacteria. The medium's selective properties and the incubation conditions (typically at 37°C for several weeks) favor the growth of *M. tuberculosis*.
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option might represent a commonly used bacterial growth medium, but it is not specified. Generally, standard bacterial media like Trypticase soy agar or Blood agar are not suitable for *M. tuberculosis* isolation due to the fastidious nature of this organism and its slow growth rate.
- **Option B:** This could potentially be another type of medium, but without specification, it's hard to directly refute. However, media like MacConkey agar are selective for gram-negative bacteria and would not support the growth of *M. tuberculosis*.
- **Option D:** This option might suggest a medium like Sabouraud agar, which is used for fungal cultures. While *M. tuberculosis* can be acid-fast, it is not a fungus, and Sabouraud agar would not be appropriate for its isolation.
## **Clinical Pearl / High-Yield Fact**
A critical point to remember is that the diagnosis of TB involves not just the identification of acid-fast bacilli but also the culture of *M. tuberculosis* for confirmation and drug susceptibility testing. The use of Lowenstein-Jensen medium or more rapid systems like BACTEC or MGIT (Mycobacteria Growth Indicator Tube) can significantly aid in the diagnosis and management of TB, especially in HIV-positive individuals who are at higher risk of developing active TB disease.