When a bacterium evolves resistance to a particular antibiotic, it's problematic. When it evolves defenses against antibiotics in general, as Pseudomonas aeruginosa has done, it's terrifying. But now researchers have devised an antibiotic that attacks the germ in a completely new way that appears to overwhelm those defenses.
P. aeruginosa is a highly adaptable bacterium that lives almost everywhere. Although a healthy immune system can stop it from causing serious problems, it mercilessly exploits almost any weakness in immuno-compromised people. It is the fourth most common cause of hospital-acquired infections, attacking burn victims and triggering septicemia and pneumonia in leukemia and AIDS patients. Pseudomonas-induced lung infections contribute to the deaths of almost all cystic fibrosis patients.
The bacterium is resistant to antibiotics because of its nearly impermeable cell wall, which makes it very difficult for the drugs to enter the microbe. And if they do sneak past security, the antibiotics may have a very short stay: the bacterium has evolved "efflux pumps" that eject unwanted chemicals. Many infected with P. aeruginosa have to be treated with antibiotics previously considered too toxic for human use.
(see abstract at http://www.sciencemag.org/cgi/content/abstract/327/5968/1010)