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Leech gut microbiome resistant to antibiotics

In a world where a scarcity in antibiotics’ efficiency is occuring, countless research in response to find more successful medicine to combat pathogenic bacteria is severely compromised.

Antibiotic resistance is widely seen in common infections from pneumonia to simple skin infections. They have greatly amassed an increase in hospital diseases which is met through our improper use of these medicines. While our ultimate goal is to find alternative treatment to contagious diseases, microorganisms tend to leap out, spread nonchalantly and seek to invade our unsuspecting bodies effortlessly.

 

Leech gut biota

Leeches are bloodsucking animals who preferably thrive in aquatic resources such as marsh, rivers, and ponds. These segmented parasites tend to have medicinal properties and is used to heal wounds including having the ability to aid blood circulation in the body.

On a study by Michele Maltz, a scientist from the University of Connecticut, analysed the metagenome of Hirudo verbana - a medicinal leech tending to have countless gut symbionts specifically the bacterium Aeromonas veronii.

In this study, they utilized gene pyrosequencing to further explore the microbial composition of the leech digestive tract, confirming the dominance of two microorganisms, the Rikenella-like bacterium and A. veronii.

They also found the presence of a Proteus strain as a newly identified resident in the leech crop which was then confirmed using fluorescence in situ hybridization (FISH).

Antibiotic resistance in leeches sucks.

Science News has reported about a bacterium found in leeches’ guts which needs exposure to only 0.01 micrograms per milliliter of ciprofloxacin to become resistant to that drug. That’s about 400 times less than the amount of antibiotics thought to trigger drug resistance in this species of bacteria, says Joerg Graf, a microbiologist at the University of Connecticut.

Certain leeches are approved for medical use by the U.S. Food and Drug Administration to help patients heal from reconstructive surgery. The slimy creatures suck up blood and secrete anticoagulants, aiding towards tissue growth.

In the early 2000s, researchers noticed an uptick in antibiotic-resistant infections in these patients that were caused by the Aeromonas bacteria found in Hirudo verbana, one of several medicinal leech species. Scientists analyzed the contents of leeches’ stomachs using mass spectrometry, and found drug-resistant bacteria as well as low levels of both ciprofloxacin and enrofloxacin, a veterinary antibiotic used on poultry farms. The researchers say the leeches may have been exposed to these antibiotics through poultry blood used for food on leech farms.

Graf suggests that leech farmers eliminate ciprofloxacin and other antibiotics from their operations. But Aeromonas is also found in freshwater environments. “It is concerning because similarly low amounts [of antibiotics] have been detected in the environment,” he says.

It’s unclear if Aeromonas alone has this lower drug resistance threshold, or if other bacteria can also become resistant at a lower threshold. If so, that could complicate global efforts to prevent drug-resistant infections.


 

Antibiotic resistance

As obtained from Science Daily, a scientific research published in mBio, provides proof that tiny levels of antibiotics found in the environment can encourage bacterial resistance.

Microbiologist Joerg Graf from the Department of Molecular and Cell Biology studies how bacteria can live inside animals' digestive tracts without making the animals sick, and leeches are a perfect study case; with only two major types of bacteria living inside them, the relationship is relatively simple.

It was a strain of Aeromonas that is usually seen in leeches. They would feed the Aeromonas strain to a leech and later on check how well the strain was growing in its gut. This time, the Aeromonas strain was having trouble. Lidia Beka, a graduate student in his lab, had pursued the cause.

"For some reason, it was having a tough time surviving in its native habitat," says Beka.

At the same time, plastic surgeons began to report problems with patients getting infected with Aeromonas bacteria resistant to ciprofloxacin, an important antibiotic. The patients had all been treated with leeches to improve blood flow at surgical wound sites. Aeromonas bacteria are a large and diverse group, and many of them can live on blood, which may cause infections if they get into wounds. But normally they are easily treated with ciprofloxacin, and there would be no source of Cipro-resistant Aeromonas in a hospital. The drug-resistant Aeromonas had to have come from the leeches -- but how? The animals are raised on specialty farms, fed a controlled diet and used only once, on a single patient.

"Without ever having been in a hospital, without having seen a patient, these leeches contained Cipro-resistant bacteria," Graf said.

When the leeches emerge from a very cold storage, they become hungry for blood. And they're not picky about where it comes from. Leeches are equal opportunity blood suckers. So when the mad cow disease outbreak made it undesirable to use cattle blood, a major medical leech farmer in Europe switched to feeding the leeches poultry blood instead.

This posed an intriguing question. What if chicken blood was contaminated with antibiotics? They analyzed the gut contents of leeches from the farm that fed poultry blood, and found traces of both ciprofloxacin and enrofloxacin. But the amount of antibiotic present was vanishingly low. Just around 0.01 micrograms per milliliter, four hundred times less than the concentration would make bacteria survive in order to be considered "resistant." Still, leeches from other farms -- in whose guts the test strain of Aeromonas still grew fine -- they haven't detected any antibiotics in their intestines.

They isolated Aeromonas strains from leeches contaminated with antibiotics, and sequenced their genomes. Two colleagues, Matt Fullmer and Peter Gogarten, confirmed that they contained three bits of DNA, two genes with mutations and a plasmid, necessary for resistance to Ciprofloxacin. Having gene mutations essential for DNA replication is biologically costly. The bacteria would only keep them if they were useful for their own survival.

"This was the first time that such low levels of antibiotics were observed in the natural environment. Levels of antibiotic 100x below the clinical breakpoint allowed the resistant bacteria to outgrow the sensitive bacteria in a million-fold!" Graf says. This is worrisome, because ciprofloxacin and related drugs don't disintegrate very well in the environment. They usually persist and can be remotely found in hospital wastewater, from pharmaceutical manufacturers and farms, and even sometimes in sewage. And, apparently, in poultry blood.

The use of antibiotics has been banned in poultry farms in the US, but not in Europe. And because antibiotics are present in hospital, pharma and sewage wastewater at such low levels, these other sources are generally unregulated. If we don't clean up our waste disposal practices, we risk making some of our most important antibiotics useless.

 

Gut bacteria

The bacteria found in the leech gut is essential for many medicinal purposes that the animal has offered. Aeromonas was found to obtain the substance hemolysin, which is used to lyse erythrocytes in crops. However, this is also a human pathogen and can cause infections in patients receiving leech therapy,thus sellers attempt to reduce the Aeromonas population in an effort to reduce wound infections and septicemia. More comprehensive surveys of animals from different leech farms as well as field caught animals are needed to determine which of the additional organisms identified belong to the core microbiome, to a transient population that persists in the gut or organism due to a disturbed niche.

With these posing a huge threat to our problem on antibiotic resistance, it is still not too late to obtain substantial information from these little critters to associate severe infections from the environment.

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