Humble fly may be super bug's match
The advertising jingle has Louie the fly singing "I'm bad and mean and mighty unclean".
Being
dirty is hardly surprising, given where flies hang out. But what do
flies have that stops them from being overrun by infections?
This
thought occurred to PhD student Joanne Clarke and her colleagues at the
Department of Biological Sciences at Macquarie University, as they
discussed where the next generation of antibiotics might come from.
"Most antibiotics were originally isolated from bacteria," Clarke said. "But we've pretty much exhausted these."
As
Clarke and her supervisors, Professor Andrew Beattie and Associate
Professor Michael Gillings, said in Australasian Science magazine:
"Microbes that produce an antibiotic may not be sensitive to that
particular antibiotic, otherwise they would kill themselves.
"Consequently
it seems likely that for every antibiotic produced [from bacteria],
there is at least one natural mechanism of resistance."
And that's the big problem. Bacteria are increasingly resistant to the present range of antibiotics, the so-called "super bugs".
The
idea of looking to insects for new ones is that the bacteria which
cause us so many problems won't have the genes to resist them, yet.
Insects
are a likely source of antimicrobials not only because of where they
live, but how they live. For example, in the close confines of a hive,
one sick individual could wipe out the entire colony if there wasn't
some way of controlling the spread of disease.
Clarke studied insects from "pretty yucky" environments.
"I
looked at the sheep blowfly, the common housefly and the vinegar fly,"
she said. "I used the Queensland fruit fly as a control because it lays
its eggs in fresh fruit."
Clarke
tested material extracted from the flies on four microbes: candida
yeast, E.coli, golden staph and a common soil bacterium, all of which
are known to cause infections in humans.
Clarke
found that adults from each test species of fly produced something
which prevented all the different microbes from growing.
"I
also looked at the different life stages of the flies," she said. "I
predicted there wouldn't be much expression of antibiotics in pupae
because they have a protective casing - they're not feeding and don't
come into contact with other flies - and, in general, that's what I
found."
The
logical next step would be to isolate and identify the chemicals in the
fly extract. But, as is increasingly the case in science, the path is
not going to be smooth.
"Although
industry very generously funded my PhD project for three years, they
chose not to renew the funding," Clarke said. "Unless someone else
funds the research, it stops at this point."
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The new buzz on antibiotics
The
surface of flies is the last place you would expect to find
antibiotics, yet that is exactly where a team of Australian researchers
is concentrating their efforts.
Working
on the theory that flies must have remarkable antimicrobial defences to
survive rotting dung, meat and fruit, the team at the Department of
Biological Sciences, Macquarie University, set out to identify those
antibacterial properties manifesting at different stages of a fly’s
development.
"Our
research is a small part of a global research effort for new
antibiotics, but we are looking where we believe no-one has looked
before,” said Ms Joanne Clarke, who presented the group’s findings at
the Australian Society for Microbiology Conference in Melbourne this
week. The project is part of her PhD thesis.
The
scientists tested four different species of fly: a house fly, a sheep
blowfly, a vinegar fruit fly and the control, a Queensland fruit fly
which lays its eggs in fresh fruit. These larvae do not need as much
antibacterial compound because they do not come into contact with as
much bacteria.
Flies
go through the life stages of larvae and pupae before becoming adults.
In the pupae stage, the fly is encased in a protective casing and does
not feed. "We predicted they would not produce many antibiotics," said
Ms Clarke.
They did not. However the larvae all showed antibacterial properties (except that of the Queensland fruit fly control).
As
did all the adult fly species, including the Queensland fruit fly
(which at this point requires antibacterial protection because it has
contact with other flies and is mobile).
Such
properties were present on the fly surface in all four species,
although antibacterial properties occur in the gut as well. "You find
activity in both places," said Ms Clarke.
"The reason we concentrated on the surface is because it is a simpler extraction.”
The
antibiotic material is extracted by drowning the flies in ethanol, then
running the mixture through a filter to obtain the crude extract.
When
this was placed in a solution with various bacteria including E.coli,
Golden Staph, Candida (a yeast) and a common hospital pathogen,
antibiotic action was observed every time.
"We
are now trying to identify the specific antibacterial compounds," said
Ms Clarke. Ultimately these will be chemically synthesised.
Because
the compounds are not from bacteria, any genes conferring resistance to
them may not be as easily transferred into pathogens. It is hoped this
new form of antibiotics will have a longer effective therapeutic life.
الرئيسية 
موضوع: حديث الذبابة إعجاز علمي موثق من المجلات العلمية الأجنبية 