M & M & M & M

what?    

• Mycoplasma pneumoniae (causes atypical pneumonia aka walking pneumonia: insidious onset, headache, non productive cough, diffuse infiltrate, respiratory symptoms don't dominate)

who? 

• Military and Minors and Misfits (prisoners)

how? 

• IgM (which causes cold agglutination and lysis of rbc which can lead to hemolytic anemia)
• bullous Myringitis (bullae on the tympanic membrane)

Tx = erythromycin or tetracycline. resistant to penicillin because? come on gander a guess (think MOA of penicillin and you'd understand immediately).

if you guessed coz it has no cell wall, good for you =) it's the only bacterial membrane with cholestrol. so it can't be seen on gram stain.