Resistencia

asThe Challenge
of Antibiotic Resistance
Certain bacterial infections now defy all antibiotics. The resistance
problem may be reversible, but only if society begins to consider how
the drugs affect “good” bacteria as well as “bad”
by Stuart B. Levy

trol—have become increasingly common.
What is more, strains of at least three
bacterial species capable of causing lifethreatening illnesses(Enterococcus faecalis, Mycobacterium tuberculosis and
Pseudomonas aeruginosa) already evade
every antibiotic in the clinician’s armamentarium, a stockpile of more than
100 drugs. In part because of the rise in
resistance to antibiotics, the death rates
for some communicable diseases (such
as tuberculosis) have started to rise
again, after having declined in the industrial nations.
Howdid we end up in this worrisome,
and worsening, situation? Several interacting processes are at fault. Analyses of
them point to a number of actions that

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OLIVER MECKES Photo Researchers, Inc.

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OLIVER MECKES Photo Researchers, Inc.

aureus, a major cause of hospital-acquired infections, has thus moved one
step closerto becoming an unstoppable
killer.
The looming threat of incurable S.
aureus is just the latest twist in an international public health nightmare: increasing bacterial resistance to many antibiotics that once cured bacterial diseases readily. Ever since antibiotics
became widely available in the 1940s,
they have been hailed as miracle drugs—
magic bullets able to eliminate bacteria
withoutdoing much harm to the cells
of treated individuals. Yet with each
passing decade, bacteria that defy not
only single but multiple antibiotics—and
therefore are extremely difficult to con-

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L

ast year an event doctors had
been fearing finally occurred.
In three geographically separate patients, an often deadly bacterium,
Staphylococcus aureus,responded poorly to a once reliable antidote—the antibiotic vancomycin. Fortunately, in those
patients, the staph microbe remained
susceptible to other drugs and was eradicated. But the appearance of S. aureus
not readily cleared by vancomycin foreshadows trouble.
Worldwide, many strains of S. aureus
are already resistant to all antibiotics except vancomycin. Emergence of forms
lackingsensitivity to vancomycin signifies that variants untreatable by every
known antibiotic are on their way. S.

Staphylococcus aureus

Acinetobacter

Enterococcus faecalis

Neisseria gonorrhoeae

Causes blood poisoning,
wound infections and pneumonia; in some hospitals, more
than 60 percent of strains are
resistant to methicillin; some
are poised for resistance to all
antibiotics (H/C;1950s)

Causes blood poisoning
in patients with compromised
immunity (H, 1990s)

Causes blood poisoning and
urinary tract and wound
infections in patients with
compromised immunity; some
multidrug-resistant strains are
untreatable (H, 1980s)

Causes gonorrhea;
multidrug resistance now
limits therapy chiefly to
cephalosporins (C; 1970s)

46

Scientific American March 1998Copyright 1998 Scientific American, Inc.

Haemophilus
influenzae
Causes pneumonia, ear
infections and meningitis,
especially in children. Now
largely preventable by
vaccines (C; 1970s)

The Challenge of Antibiotic Resistance

and they should not be administered for
viral infections, over which they have no
power.
A Bad Combination

A

lthough many factors can influence
whetherbacteria in a person or in
a community will become insensitive to
an antibiotic, the two main forces are
the prevalence of resistance genes (which
give rise to proteins that shield bacteria
from an antibiotic’s effects) and the extent of antibiotic use. If the collective
bacterial flora in a community have no
genes conferring resistance to a given
antibiotic, the antibiotic will successfully...