<prompt> Mycoplasmas differ from chlamydiae in that they areSusceptible to penicillinAble to grow on artificial cell-free mediaAble to cause urinary tract infectionAble to stain well with Grams stain  <response>: Mycoplasmas lack a rigid cell wall and are bound by a triple-layer unit membrane. For this reason, they are completely resistant to the action of penicillins. Unlike the chlamydiae, they can replicate in cell-free media. 