Mycoplasma

Mycoplasmatacae are the tiniest free-living organisms capable of replicating. They are unique bacteria because they lack cell walls, having only cell membrane with sterols for protection from the environment. The lack of a cell wall explains why penicillin and other antibiotics do not attack mycoplasmatacae. Two pathogenic species are Mycoplasma pneumoniae and Ureaplasma urealyticum.

Mycoplasma pneumoniae 
It is the leading cause of bronchitis and pneumonia in young adults. The mild symptoms of gradual fever, sore throat and cough is called walking pneumonia. However, it is unknown why 7% of infected patients develop severe symptoms of erythema multiforme or Stevens-Johnson syndrome.

Ureaplasma urealyticum 
Found in urine and breaks down urea. It is part of normal flora in 60% of sexually active women. It can infect the lower urinary tract, causing non-gonococcal urethritis.