How microbes fight back
Often it is the chemical structure of individual bacterial cells that enables them
to resist the onslaught of antibiotics. If, for example, a patient fails to take a
full course of antibiotics, resistant bacteria don't get hit with a dose large enough
to kill them. The surviving bacteria enjoy reduced competition, and each time the
same antibiotic is used, resistant bacteria make up an ever-larger percentage of the
overall population. Mutations can affect antibiotic resistance even more directly,
by actually increasing the strength of resistance in individuals. Over time, these
individual changes can strengthen a population's overall level of resistance.
Streptococcus pneumoniae, or pneumococcus, is the most common cause of serious
infection in the United States. More than 7 million Americans suffer from pneumococcal
infections annually; forty thousand of these people die each year. No other bacterium
is known to cause more death in the United States.
The spread of disease
Pneumococcus bacteria are spread from person to person through sneezing, coughing, and
contact with surfaces. When a person is first exposed, the bacteria cling to the surface
of cells lining the respiratory tract. The most common illnesses caused by Streptococcus
pneumoniae are otitis media (middle ear infection), pneumonia, bacteremia, and
Since the early 1940s, antibiotic use has reduced mortality rates among patients with
pneumococcal infections by 90 percent. Until recently, Streptococcus pneumoniae
remained extremely susceptible to penicillin and penicillin-like antibiotics.
As of 1997, more than half of all pneumococcus bacteria strains were evolving resistance
or had become completely resistant to penicillin. The search for alternative antibiotics
to treat bacterial illnesses has been only marginally successful.
End of the miracle
Strains of at least three other life-threatening bacterial species -- including the
species that causes tuberculosis -- have evolved resistance to every available
antibiotic, a stockpile of more than 100 drugs. The list of microbes that have
developed resistance to at least one antibiotic is growing quickly.