04.2020 | THE SCIENTIST 19To test the efficacy of the method,
Braeckmans, Coenye, and colleagues
grew Pseudomonas aeruginosa or Staph-
ylococcus aureus, two bacterial species
commonly found in chronic wounds,
into hardy biofilms in lab dishes. They
then tested how well a panel of com-
mon antibiotics and antiseptics killed
bacteria in biofilms that were laser-
zapped, compared with those that were
left untouched or broken up with sound
or manual stirring—processes known to
break up biofilms, but which run the risk
of heating up healthy tissue or sending
fragments of destroyed biofilms into the
bloodstream, respectively. Previous work
by Braeckmans showed that the trans-
fer of energy from laser zaps to vapor
nanobubbles is highly efficient, and thus
doesn’t generate excess heat. And while
the nanobubbles generate high-energy
shock waves when they collapse, these
waves aren’t powerful enough to frag-
ment a biofilm.
Laser-triggered nanobubbles, the
team found, were often as effective at
aiding antibiotic delivery as breakingup biofilms using sound or stirring. One
antibiotic became 100 percent effective
against a biofilm zapped with just five
rounds of laser fire, the team notes in a
paper published in the December issue
of Biofilm (1:100004, 2019).
“I think this is a really cool idea,” says
Kendra Rumbaugh, a microbiologist at
Texas Tech University Health Sciences
Center in Lubbock who was not involved
in the study. “They’ve got some impor-
tant next steps and have to show that it
works in animals, but I think they’re on
the right track.”
Paul Stoodley, a microbiologist at
Ohio State University in Columbus,
thinks the findings are encouraging and
warrant further investigation. But he
cautions that the approach would likely
only be applicable to skin-deep infec-
tions, and not to biofilms that attack
bone or cause persistent urinary tract
infections, for example. “If you’re using
lasers, you need line of sight,” says Stood-
l e y, who was not involved in the study. “If
you’ve got a biofilm inside the body, laser
light is going to be [challenging].”The findings come with other cave-
ats. Certain antimicrobials worked just
as well on biofilms that hadn’t been
zapped as on those that had, suggesting
that those drugs didn’t need the laser-
triggered implosions in the first place.
And the laser bursts sometimes enhanced
a drug’s effect on biofilms of one bacterial
species but not another.
Nevertheless, Braeckmans and Coe-
nye’s approach might work against a
wider range of biofilm-forming bacteria
than other biofilm-busting strategies
under development. Some scientists
are testing small molecules that fool
biofilm-bound bacteria into resuming
life as single cells, for example, while
others are searching for enzymes that
chop up the sugary matrix that makes
biofilms so impenetrable. These strat-
egies will likely only work for biofilms
containing certain bacterial species,
says Rumbaugh, while the laser-trig-
gered nanobubbles developed by
Braeckmans and Coenye could in the-
ory blast through biofilms regardless of
their composition.
The Belgian group plans to develop
the technique in future studies and
will test the safety and efficacy of the
approach in more-complex skin and
animal models. Coenye says a natural
place to start would be with a laboratory
mimic of skin in which structural mole-
cules such as collagen sit atop a mixture
of blood and bacterial growth medium.
Researchers could infect this skin model
with biofilm-forming bacteria to test
whether laser nanobubbles combined
with antibiotics help clear the infections.
“This approach is, I think, poten-
tially widely applicable,” Coenye says.
“One of the goals I have, before I retire,
is to be able to say that I’ve contributed
to bringing one new drug or one new
approach to treat biofilm-related infec-
tions to patients.”
—Jonathan WosenZAPPING THROUGH BARRIERS: Researchers
in Belgium used a setup involving lasers to aid
the delivery of antibiotics into bacterial biofilms.COURTESY OF KEVIN BRAECKMANS