Ureaplasma and mycoplasma are among the smallest free-living bacteria. Unlike other bacteria however, these organisms lack a cell wall and live inside cells. However, they can also live in cultures outside of cells, similar to the way viruses live. Unlike viruses, though, they can be killed by certain antibiotics. Symptoms can be "silent" or can cause noticeable symptoms such as discharge, burning, urinary frequency, urinary urgency, and pain. Special laboratory tests and cultures (a method of multiplying the bacteria to better identify them) is required.