Superbugs
The new generation of resistant infections is almost impossible to treat.
by Jerome Groopman

In August, 2000, Dr. Roger Wetherbee, an infectious-disease expert at New York University’s Tisch Hospital, received a disturbing call from the hospital’s microbiology laboratory. At the time, Wetherbee was in charge of handling outbreaks of dangerous microbes in the hospital, and the laboratory had isolated a bacterium called Klebsiella pneumoniae from a patient in an intensive-care unit. “It was literally resistant to every meaningful antibiotic that we had,” Wetherbee recalled recently. The microbe was sensitive only to a drug called colistin, which had been developed decades earlier and largely abandoned as a systemic treatment, because it can severely damage the kidneys. “So we had this report, and I looked at it and said to myself, ‘My God, this is an organism that basically we can’t treat.’ ”

Klebsiella is in a class of bacteria called gram-negative, based on its failure to pick up the dye in a Gram’s stain test. (Gram-positive organisms, which include Streptococcus and Staphylococcus , have a different cellular structure.) It inhabits both humans and animals and can survive in water and on inanimate objects. We can carry it on our skin and in our noses and throats, but it is most often found in our stool, and fecal contamination on the hands of caregivers is the most frequent source of infection among patients. Healthy people can harbor Klebsiella to no detrimental effect; those with debilitating conditions, like liver disease or severe diabetes, or those recovering from major surgery, are most likely to fall ill. The bacterium is oval in shape, resembling a TicTac, and has a thick, sugar-filled outer coat, which makes it difficult for white blood cells to engulf and destroy it. Fimbria—fine, hairlike extensions that enable Klebsiella to adhere to the lining of the throat, trachea, and bronchi—project from the bacteria’s surface; the attached microbes can travel deep into our lungs, where they destroy the delicate alveoli, the air sacs that allow us to obtain oxygen. The resulting hemorrhage produces a blood-filled sputum, nicknamed “currant jelly.” Klebsiella can also attach to the urinary tract and infect the kidneys. When the bacteria enter the bloodstream, they release a fatty substance known as an endotoxin, which injures the lining of the blood vessels and can cause fatal shock.

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