Drugs to fight superbugs becoming ineffective

At one time methicillin-resistant Staphylococcus aureus (MRSA) was the superbug of all superbugs. But this past January, a report issued by the Infectious Diseases Society of America warned that drug-resistant strains of Acinetobacter baumannii and two other microbes - Pseudomonas aeruginosa and Klebsiella pneumoniae - may soon become just as deadly as MRSA.

Why are these bacterias nearly impossible to treat? They belong to a group of "gram-negative" bacteria. These superbugs are wrapped in a double membrane and give safe harbor to enzymes that "chew" up many antibiotics. As a result, they are extremely resistant to drugs. Moreover, because gram-negative bacteria can enter the body by way of catheters, IVs, ventilators or wounds, seriously ill hospitalized patients, such as premature infants, very old patients and ICU patients who have recently undergone surgery, are particularly prone to infection. Once the bacteria evades the body, it can cause pneumonia, urinary tract infections, as well as bone, joint and bloodstream infections. "We're literally running out of drugs to treat gram-negatives," says Dr. Brad Spellberg, an infectious disease specialist at Harbor-UCLA Medical Center. "And there is nothing in the pipeline right now."

Carbapenems, a class of broad-spectrum antibiotics, are known as the drug of last resort used to treat gram-negative bacteria. "The carbapenems are the best gram-negative drugs we have," says Dr. Helen Boucher of Tufts University, an infectious disease specialist. However, she adds that "these bugs have found a way to make an enzyme that dissolves these drugs. That means our best gun is ineffective." Unfotunately, these drugs are beginning to fail, forcing doctors to turn to older more toxic medications. For example, the drug colistin can cause kidney damage and deafness, and as a result, its use has dropped dramatically.

News Release: Deadly bacteria defy drugs, alarming doctors www.latimes.com February 17, 2009