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Superbug’s DNA
reveals its past
By Tina Hesman Saey
Sometimes natural selection gets a helping hand from humans. In tracing the
genetic history of a nasty strain of pneu-monia-causing bacteria, a new study
shows how antibiotics and vaccines
helped shape the microbe’s evolution.
An international team deciphered
the complete genetic blueprints of 240
samples of a drug-resistant strain of
Streptococcus pneumoniae taken from
people in 22 countries between 1984
and 2008, allowing the researchers to
see how the bacteria changed over time.
This strain, known as the Pneumococcal Molecular Epidemiology Network
clone 1 or PMEN1, was first recognized in
a hospital in Barcelona in 1984. But the
new analysis indicates the strain probably first arose around 1970, the team
reports in the Jan. 28 Science.
“When this clone emerged, it emerged
into a world in which penicillin was frequently used,” says Stephen Bentley, a
study coauthor and molecular microbiologist at the Wellcome Trust Sanger
Institute in Hinxton, England. The strain
wasn’t killed by penicillin, and so spread
quickly. The new study reveals some of
the genetic tricks the organism used to
develop drug resistance.
Since its emergence, the strain has
changed one of its DNA letters (the
chemical units of its genetic material) about every 15 weeks, the analysis
finds. That rate of mutation is rapid
but similar to rates seen in the deadly
antibiotic-resistant Staphylococcus
aureus bacterium called MRSA.
The PMEN1 strain also occasionally
swaps or recombines DNA with other
bacteria, and such recombination may
be far more important in developing
drug resistance. Each DNA-swapping
episode brings about 72 single-letter
changes on average and sometimes
introduces entirely new genes, or new
versions of genes. “Although it’s already
got a winning formula for spread-
ing around the globe, it’s constantly
rearranging its DNA,” says Bentley.
A direct route to reprogramming
New method transforms skin cells into beating cardiac cells
Instead of taking
mouse skin cells all the
way back to a stem cell
state and then coaxing them to form
heart tissue, the researchers switched
the cells directly by briefly introducing
the reprogramming factors and then
giving the skin cells a bath in chemicals
that induce heart cell development.
Others have turned skin cells directly
into nerve cells (SN: 2/27/10, p. 5), and
previous studies have grown heart cells
from embryonic-like stem cells. But the
new process is faster.
It took 11 days to make
beating cells, whereas
it could take weeks
to convert skin cells
to an embryonic-like
state and then more
time to develop them
into heart cells.
Direct reprogram-
ming may one day
be used to grow new
hearts for transplant
from a patient’s own skin or to help repair
damage after heart attacks. Scientists
also want to use such cells to learn how
some genetic defects affect development
of the heart and other organs. s
Skin cells can now be turned
directly into heart muscle
cells (shown) in just 11 days.
By Tina Hesman Saey
Skin cells can be converted directly into
beating heart cells, a new study shows.
The transformation occurs with a little
help from cellular reprogramming factors that
are usually used to make
embryonic-like stem
cells, scientists from the
Scripps Research Institute and the University
of California, San Diego
report online January 30
in Nature Cell Biology.
