Jan 21 05:25

 The drug-resistant "superbugs" that have cut a swathe through day care
centers, schools, locker rooms and prisons across the United States in the
last five years stem from one rapidly evolving bacterium, US scientists
said Monday.
Scientists studying the genetic make-up of these bugs, which are resistant
to almost all antibiotics, say they are nearly identical clones that have
emerged from a single bacterial strain, which they have dubbed USA300.

"The USA300 group of strains appears to have extraordinary transmissibility
and fitness," said Frank DeLeo, a researcher with the National Institute of
Allergy and Infectious Diseases (NIAID) in Hamilton, Montana.

"We anticipate that new USA300 derivatives will emerge within the next
several years and that these strains will have a wide range of
disease-causing potential."

Most drug-resistant staph infections cause soft-tissue infections such as
boils that are readily treatable, but a skin infection can become a deadly
pneumonia or blood or bone infection in a matter of days if the patient
doesn't get the right drugs.

What's particularly worrying to health authorities is that the MRSA
infections, (methicillin-resistant Staphylococcus aureus) have spread
beyond their traditional hospital setting, seeding an epidemic in the wider
community.

The NIAID scientists studied the DNA of 10 patient samples of the USA300
bacterium taken from individuals treated at different US locations between
2002 and 2005. They compared the genetic sequences of the bugs to each
other and to USA300 strains used in earlier studies.

The genomes of eight of the 10 patient samples were virtually identical,
indicating they came from a common strain. The remaining two bacteria were
related to the other eight, but more distantly.

The study appears in the Proceedings of the National Academy of Sciences.