Researchers
from University of Birmingham investigated how and why a clone of E. coli
called ST131 -- dubbed a 'superbug' because it is resistant to multiple drugs
-- has become the major cause of drug resistant E. coli infections, but not so
dominant that it has wiped out other clones that do not have multi-drug
resistance.
The
number of cases of E. coli have risen by 27% from 32,309 in 2012-13 to 41,060
in 2017-18. The rise has been linked to an increase in antibiotic resistant
infections caused by so-called 'superbugs'.
The most
globally dominant clone of E. coli that is resistant to multiple drugs is
called ST131. Earlier research has shown that while ST131 emerged and rapidly
spread in the late 1990s, it caused no more than 20% of clinical cases of E.
coli once it had emerged on the scene. This is because of a type of
evolutionary selection called negative frequency dependency selection (NFDS).
It is now known that while there are
significantly dominant drug resistant clones of E. coli such as ST131 and other
new ones are emerging all the time, it seems highly unlikely that any of them
are ever going to become a completely dominant clone because this process called
NFDS controls the balance across the whole E. coli population.
As
part of the research the scientists also analysed almost 1,000 genome sequences
of strains within ST131 to see if they could find any genetic patterns that may
explain how this process happens. It was found that in the ST131 clone there
was a lot of variation in the genes that are involved in allowing the bacteria
to colonize in the human gut when compared to those in non-drug resistant
bacteria that are very closely related to ST131.
The
implications are that if a person is going to get a bloodstream or urinary
infection from E. coli it usually comes after it has colonized in the gut,
therefore we now know that genetically something has happened to this superbug
which allows it to colonise the gut far more competitively than other E. coli.
Posted by Dr. Tim Sandle, Pharmaceutical Microbiology
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