Among the mix of enzymes are proteases, which break down
Mitchell and his team tested the strength of the mutant’s
secretions against the gram-positive Staphylococcus aureus.
A cocktail of the enzymes applied to an S. aureus biofilm
degraded the slime shield and reduced the bacterium’s virulence. Biofilms can make bacteria up to 1,000 times more
resistant to antibiotics, Mitchell says. The next step, he adds,
is to see if degrading a biofilm resensitizes a gram-positive
bacterium to antibiotics.
Mitchell and his team also treated S. aureus
cells that didn’t have a biofilm with the
mutant’s enzyme mix and then exposed them
to human cells. Eighty percent of the bacteria were no longer able to invade human cells,
Mitchell says. The “acid spit” chewed up surface proteins that the pathogen uses to attach
to and invade human cells. The enzymes didn’t
kill the bacteria but did make them less virile.
No downsides yet
Predatory bacteria can efficiently eat other
gram-negative bacteria, munch through biofilms and even save
zebrafish from the jaws of an infectious death. But are they
safe? Kadouri and the other researchers have done many studies, though none in humans yet, to try to answer that question.
In a 2016 study published in Scientific Reports, Kadouri
and colleagues applied B. bacteriovorus to the eyes of rabbits
and compared the effect with that of a common antibiotic
eye drop, vancomycin. The vancomycin visibly inflamed the
eyes, while the predatory bacteria had little to no effect. The
eyes treated with predatory bacteria were indistinguishable
from eyes treated with a saline solution, used as the control
treatment. Other studies looking for potential toxic effects of
B. bacteriovorus have so far found none.
In 2011, Sockett’s team gave chickens an oral dose of pred-
atory bacteria. At 28 days, the researchers saw no differ-
ence in health between treated and untreated chickens. The
makeup of the birds’ gut bacteria was altered, but not in a way
that was harmful, she and her team reported in Applied and
Kadouri analyzed rats’ gut microbes after a treatment
of predatory bacteria, reporting the results in a study published March 6 in Scientific Reports. Here too, the rodents’
guts showed little to no inflammation. When they sequenced
the bacterial contents of the rats’ feces, the
researchers saw small differences between
the treated and untreated rats. But none of the
changes appeared harmful, and the animals
grew and acted normally.
If the rats had taken common antibiotics,
it would have been a different story, Kadouri
points out. Those drugs would have given the
animals diarrhea, reduced their appetites and
altered their gut flora in a big way. “When you
take antibiotics, you’re basically throwing an
atomic bomb” into your gut, Kadouri says.
“You’re wiping everything out.”
Both Mitchell and Kadouri tested B. bacteriovorus on human
cells and found that the predatory bacteria didn’t harm the
cells or prompt an immune response. The researchers sepa-
rately reported their findings in late 2016 in Scientific Reports
and PLOS ONE.
Microbiologist Elizabeth Emmert of Salisbury University
in Maryland studies B. bacteriovorus as a means to protect
crops — carrots and potatoes — from bacterial soft rot diseases.
For humans, she calls the microbes a “promising” therapy for
bacterial infections. “It seems most feasible as a topical treat-
ment for wounds, since it would not have to survive passage
through the digestive tract.”
There are plenty of questions that need answering first.
Mitchell guesses that there will probably be 10 more years of
rigorous testing in animals before moving on to human clini-
cal studies. But pursuing these alternatives is worth the effort.
“The drugs that we’re taking are not benign and cuddly
and nice,” Kadouri says. “We need them, but they don’t come
without side effects.” Even though a living antibiotic sounds a
bit crazy, it might be the best option in this dangerous era of
antibiotic resistance. s
s Kenneth Shatzkes et al. “Effect of predatory bacteria on the
gut bacterial microbiota in rats.” Scientific Reports. March 6,
s Alexandra Willis et al. “Injections of predatory bacteria work
alongside host immune cells to treat Shigella infection in
zebrafish larvae.” Current Biology. December 19, 2016.
Elizabeth S. Eaton is a former Science News intern and a
freelance science writer.
can efficiently eat
through biofilms and
even save zebrafish
from the jaws of an
infectious death. But
are they safe?
Seeing the difference Researchers applied a saline solution,
antibiotic or Bdellovibrio predatory bacteria to the eyes of rabbits
to compare toxicity. Eyes treated with predatory bacteria or saline
showed little inflammation. But eyes treated with the antibiotic
vancomycin were inflamed, swollen and produced mucus.
Hours after application
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