>> stenotrophomonas. >> narrator: stenotrophomonas is an entirely different kind of bacteria from staph. >> does it hurt? >> narrator: found in hospitals, it can live inside breathing tubes, and it's extremely difficult to treat. >> the problem with stenotrophomonas is, even at the outset, it's already a very resistant bacteria. there are only four or maybe five antibiotics normally that are able to treat that particular bacteria. >> narrator: addie was confronting the frightening new face of antibiotic resistance: a group of bacteria called gram- negatives. >> hoffman: so can you explain to me why these gram-negatives are so stubbornly nasty? >> gram-negative bacteria, it's a medical term and it really references the armor that surrounds the gram-negative bacteria. that armor makes it very difficult for normal antibiotics to get into the bacteria and to kill it. >> so miss addie... >> so stenotrophomonas is incredibly difficult to treat because it has that serious body armor surrounding it. >> are you guys going to come out and go that way? okay. >> narrator: the ability of gram-negati