Which bacterium causes walking pneumonia and lacks a cell wall?

Mycoplasma pneumoniae causes walking pneumonia and lacks a cell wall.

The organism is a very small bacterium that commonly causes tracheobronchitis and mild pneumonia, especially in school-age children and young adults. The phrase “walking pneumonia” reflects the often gradual, relatively mild presentation rather than a separate species or formal diagnosis.

Because M. pneumoniae has no peptidoglycan cell wall, antibiotics that target cell-wall construction, such as penicillin, do not work against it. Its cell membrane instead contains sterols, which help maintain membrane stability. This unusual biology distinguishes Mycoplasma from most medically important bacteria.

The infection spreads mainly through respiratory droplets during close contact. Symptoms can include persistent cough, fever, sore throat, and tiredness. Mycoplasma pneumoniae should not be confused with Chlamydia pneumoniae, another bacterium that can cause respiratory infection.