A Horror Story: How Leeches Helped Uncover a Terrible Truth About Antibiotic Resistance

This story[i] knocked my socks off.   Read on if you like horror stories.

Dr. Joerg Graf at the University of Connecticut is a specialist in the microbiome of leeches, which contains only two major types of bacteria.  In 2011 though, one of his graduate students was having difficulty getting one of these, Aeromonas, to grow in the leeches.  That is, the bacteria were not surviving well in what should be their natural habitat.

Many of you may know that leeches are used nowadays medicinally:  for example, to increase blood flow at the site of surgeries.  At the same time that Dr. Graf’s lab was struggling to get Aeromonas to grow in their leeches’ guts, plastic surgeons began to report Aeromonas infections in patients that were resistant to the antibiotic, Cipro.

Now, bear in mind, the leeches are raised in specialty farms, fed a controlled diet, only used in 1 patient and only 1 time.  And in these hospitals, this type of bacteria could only have come from leeches.  The question was then – how could these carefully raised organisms be spreading antibiotic-resistant Aeromonas?

The answer:  before being sent to the hospital, the leeches were fed a diet of poultry blood, and this was the source of the antibiotic-resistant bacteria. Graf analyzed the content of the leeches’ guts, the ones in which he was having hard time growing Aeromonas, and found incredibly low amounts of two antibiotics, including Cipro.  The amounts were beyond tiny – 400X less than the concentration bacteria must survive to be considered resistant.  400X!!!!!!!!  Still, it was only in these leeches that the bacteria failed to thrive.  Aeromonas grew just fine in leeches from other farms, which had no trace antibiotics in them.

To definitively determine whether or not antibiotic concentrations that low could actually matter, Graf and his lab team examined the genomes of the Aeromonas from the contaminated leeches and found that, indeed, they had mutated to allow them to survive Cipro.

Think about the implications of this!  Trace amounts of antibiotics are found in both our water and in many food animals.  It’s hard nowadays to NOT be exposed.  Is it any wonder then that antibiotic-resistant bacteria are on the rise in the industrialized world – and that our biomes are being inexorably altered?

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[i] University of Connecticut. “Antibiotic resistance in a leech’s gut: Real world evidence that negligible levels of antibiotics in chicken blood can cause bacterial resistance — and sicken people with hard-to-treat infections.” ScienceDaily. ScienceDaily, 24 July 2018. <www.sciencedaily.com/releases/2018/07/180724110127.htm>.