Poultry International - March 2018 - 25
PoultryInternational ❙ 25
drugs have become ineffective and, in some cases,
resistant bacteria may "co-select for other traits that
make them more dangerous to humans, for example,
more likely invade the bloodstream."
Complexity of emergence and spread
Pew notes that the molecular processes by which
resistance emerges, spreads and potentially disappears are complex.
Some resistant genes occur naturally, fully independent of exposure to antibiotics.
Additionally, not every antibiotic works against
every type of bacterium. For instance, an antibiotic
may be effective only in killing bacteria with a certain type of molecular structure, leaving those without that structure unaffected.
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Bacteria can acquire antibiotic resistance through
various mechanisms. It may be acquired sequentially, and how quickly this occurs depends on several
factors, including the bacterium type, the negative
effect any changes have, and the nature of antibiotic
However, bacteria can also quickly develop
resistance when they share their resistance genes.
Bacteria can also share several genes at the same
time, including those that confer traits unrelated to
resistance, which can complicate resistance dynamics through a process called co-selection.
In co-selection, resistance genes are physically
linked to genes carrying other traits. This can cause
bacteria no longer exposed to antibiotics to retain
their resistance properties. Because of this, resistance may appear or disappear significantly faster in
some situations than in others, and perhaps not at all
during a period of study. ■
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