226 ■ CHAPTER 12 Mechanisms of EvolutionEVOLUTION
Laboratory of Human Bacterial Pathogenesis at
the National Institute of Allergy and Infectious
Diseases, and bacteria evolve more quickly than
we can develop new antibiotics. It’s a vicious
cycle, he says. “As we continue to use antibiotics,
populations of microbes will develop resistance
to antibiotics.” Recently, microbes appear to be
winning the struggle. In July 2016, researchers
reported the second U.S. appearance of a super-
bug resistant to colistin, an antibiotic of last
resort. “The golden age of antibiotics appears
to be coming to an end,” the Los Angeles Times
wrote.
VRSA has not yet become as widespread
as MRSA. Scientists believe the reason may
be that staph does not handle the resistance
allele for vancomycin very well; the gene from
Enterococcus is bulky and difficult to manage,
so the staph individuals that receive the gene
are often outcompeted by other staph individu-
als in the environment. “Though it allows them
to survive, they don’t do well with it. There’s a
[survival] cost to having this resistance,” says
Gilmore. In the absence of vancomycin, staph
is better off without the resistance allele, so
perhaps staph individuals lose it or don’t pick it
up when not in the presence of the drug. VRSA
therefore remains “a rare, unstable organism
in the environment that isn’t very hardy, so it
doesn’t last and spread,” says Sievert. “That’s
the good news.”
But there’s still trepidation that staph may
adapt and get comfortable with this resis-
tance gene, just as staph adapted to methicil-
lin resistance, says Gilmore. If staph survives
and reproduces more easily with the resis-
tance gene, the gene will likely spread to staph
throughout the host/human population. “We
don’t know if that’s a possibility,” says Gilmore.
“My suspicion is that it is.” (See “How Can Yo u
Make a Difference? Help Prevent Antibiotic
Resistance!”)
In fact, the thirteenth VRSA case, from a man
in Delaware in July 2012, was not a CC5 strain,
says Gilmore—suggesting that vancomycin
resistance is spreading to other strains of staph.
“It’s disconcerting,” he adds. It seems that other
populations of staph may now also be evolving
vancomycin resistance. “The main worry is that
this would move into a strain that was highly
transmissible in the community,” adds DeLeo.
“The potential is there.”new drugs that hadn’t yet been released on the
market. “There are still some antibiotics we can
use for treatment, but we recommend those be
used very responsibly in order to maintain their
effectiveness,” says Sievert. “You don’t want to
give them out when not necessary because you
don’t want to see resistance to them. You save
them as the end of the line, so something is avail-
able if the commonly used drugs end up failing
because of resistance.” After 9 months of careful
treatment, the patient healed and was able to
keep her foot. Other cases of VRSA have simi-
larly been resolved by the use of the newer anti-
biotics and the delicate care of doctors.
But what happens when even these drugs
no longer work against staph? Pharmaceuti-
cal companies are developing few new anti-
biotics, says Frank DeLeo, acting chief of theT
he U.S. Centers for Disease Control and Prevention (CDC)
recommends the following guidelines:● Take antibiotics exactly as the doctor prescribes. Do not skip
doses. Complete the prescribed course of treatment, even when
you start feeling better.● Only take antibiotics prescribed for
you; do not share or use leftover
antibiotics. Antibiotics treat specific
types of infections. Taking the wrong
medicine may delay treatment and
allow bacteria to multiply.● Do not save antibiotics for the
next illness. Discard any leftover
medication once the prescribed
course of treatment is completed.● Do not ask for antibiotics when your
doctor thinks you do not need them.
Remember that antibiotics have side effects. When your doctor
says you don’t need an antibiotic, taking one might do more harm
than good.● Prevent infections by practicing good hand hygiene and getting
recommended vaccines.SOURCE: http://www.cdc.gov/Features/AntibioticResistance.