Which organism is identified as the causative agent of Primary Atypical Pneumonia?

Primary Atypical Pneumonia, often referred to as "walking pneumonia," is primarily caused by Mycoplasma pneumoniae. This organism is unique among bacterial pathogens due to its lack of a cell wall, which differentiates it from many other bacteria, making it resistant to common antibiotics that target cell wall synthesis.

Mycoplasma pneumoniae typically infects the respiratory tract and is known for causing less severe symptoms compared to classical pneumonia, which is often associated with more virulent pathogens. The infections tend to be more widespread, especially in crowded settings such as schools and military barracks, and commonly affect younger individuals.

The other organisms listed have different associations: Streptococcus pneumoniae is a common cause of typical bacterial pneumonia; Bacillus, particularly Bacillus anthracis, is associated with anthrax; and Neisseria typically refers to pathogens like Neisseria meningitidis or Neisseria gonorrhoeae, which are associated with meningitis and gonorrhea, respectively. Thus, Mycoplasma pneumoniae is recognized as the specific causative agent of Primary Atypical Pneumonia due to its distinct characteristics and the nature of the illness it produces.