Mycoplasma pneumoniae is a very special bacterial species since it does not have a wall1. Its flexible membrane can invaginate, sometimes giving saccular or sea urchin shapes.
Mycoplasma pneumoniae is spread from person to person by droplets2 of respiratory secretions. It is a common agent of pneumonia, causing epidemics in school-aged children, often in the fall. Diagnosis is usually based on PCR and this diagnosis is important since, due to the absence of a wall, mycoplasma is naturally resistant to all penicillin derivatives, which generally target components of the bacterial wall.
Note that there are other species of mycoplasmas, some of which can cause human disease at the urogenital level and others represent veterinary pathogens. Mycoplasma is usually treated with macrolides or doxycycline.