Acinetobacter baumanii is a gram negative rod that is a strict aerobe, non-motile and grows in reddish purple colonies. It is found everywhere in the soil, food, and water, and is normal flora of humans with 25% of people having it on their skin, and 75% of people have it on their pharynx. Because it lives on us all the time, it is subjected to all the antibiotics that people take, and so it has evolved to be highly antibiotic resistant. The only antibiotics that work at all against this bug have side effects like nausea/vomiting, siezures, and other toxicity. Soldiers who spend time in Iraqi hospitals often come home infected with it. It causes suppurative infections in any organ. The cost of war just got higher. Now we have this bug in our hospital systems, and it is gaining prevalence as a nosocomial infection. It most frequently causes pneumonia, but also infects the brains, eyes, hearts, bones and joints, blood, the pancreas, liver and urinary tract. You don't want it. Luckily, if you are healthy, it won't get you. You live in equilibrium with it. But if you are ever stretched to your last stand in a hospital, it may be something like this that finishes you off.
A better known nosocomial infection is Pseudomonas aeruginosa. It is also a gram negative rod but is limited to where it can colonize because it is an obligate aerobe. So it only grows on surfaces where it has a good air supply, such as the insides of the lungs, or in burns. It also likes the respiratory mucus of cystic fibrosis patients. It grows into a thick "slime" which is actually a colony of bacteria that begins to function like a tissue. The outer layers that protect the inside from antibiotics or immune agents. The cells of the tissue signal each other, and when P. aeruginosa reaches a QUORUM it begins to turn on the genes that make it lethal. It produces a range of enzymes to digest tissues (known as invasins) and a couple of exotoxins that impair the host's ability to make proteins (exotox A) and cause part of the host's immune system to self destruct (the T cells are rapidly activated and apoptosis induced by exoenzyme S). If you grow the slime on an agar plate it looks blue-green and swells sweet, grapey by some reports. Don't let the sweet smell lull you.
Luckily for most of us, the slime never gets started good enough to slam us with its full power. Our immune systems and functioning respiratory cilia get that shit out. But if you're sick, and you go to the hospital, you don't want to know what I'm about to tell you. P. aeruginosa is the #2 cause of nosocomial pneumonia, osteochondritis and surgical site infections. It's the #3 cause of nosocomial UTI's. The #6 cause of nosocomial blood sepsis. It's the #1 cause of pneumonia in ICU patients, and is the most common cause of death among patients with cystic fibrosis. Once it reaches a quorum it is rapidly fatal. I have no idea if there are any antibiotics left that can kill it. And here's the topper. It lives in hot tubs and swimming pools. Don't let your immune system get beat down too far. These bugs are frightening.