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article imageEssential Science: Triclosan affects responses to antibiotics

By Tim Sandle     Feb 25, 2019 in Science
The chemical triclosan, found in many household products, like toothpaste and mouthwash, has been found to inadvertently make some bacteria more resistant to antibiotics.
The research, which comes from Washington University in St. Louis, has shown how triclosan exposure over time has the potential to trigger some bacteria to enter a state whereby they can tolerate concentrations of antibiotics that would otherwise kill them. This phenomenon has been noted with the types of antibiotics typically used to treat urinary tract infections.
Triclosan is an antibacterial and antifungal agent, developed during the 1960s, and present in some consumer products. It is an organic compound in the form of a white powdered solid, with a slight aromatic, phenolic odor; and the mechanism of action is similar to triclocarban.
In terms of microbial action, at higher concentration triclosan kills bacteria by attacking multiple cytoplasmic and membrane targets. At lower concentrations it can inhibit bacterial growth, by disrupting fatty acid synthesis.
A downside with triclosan is that it is very stable, remaining in the body and in the environment for long time periods of time. Triclosan’s efficacy as an antimicrobial agent remains controversial.
Triclosan: safety and efficacy
The U.S. Food and Drug Administration, in 2017, raised concerns, relating to both safety and lack of efficacy data, in relation to triclosan. This led to triclosan being removed from most consumer soaps (and to other over-the-counter consumer antiseptic products). However, the chemical continues to be used in other products.
File photo of soap and water
File photo of soap and water
With the safety issue, short-term animal studies indicate that exposure to high doses of triclosan is associated with a decrease in the levels of some thyroid hormones. It is unknown, as yet, whether the same effect takes place with humans. Similar concerns about it have previously prompted the European Union to ban triclosan in personal care products.
New research
The new research has been conducted in mice, and it demonstrates the extent that triclosan exposure limits the mammalian body's ability to respond to antibiotic treatment for urinary tract infection. This is based on a cellular mechanism that enables triclosan to interfere with antibiotic treatment.
Using mice, the researchers were able to replicate in mice that were given triclosan-spiked water to drink, urine triclosan levels similar to those reported in humans. This allowed the researchers to test the effects of triclosan exposure at a similar level to humans. A control group of mice that drank water without triclosan was used, so that the bacterial levels in the urinary tract could be compared.
H. pylori is a helix-shaped (classified as a curved rod  not spirochaete) Gram-negative bacterium ab...
H. pylori is a helix-shaped (classified as a curved rod, not spirochaete) Gram-negative bacterium about 3 μm long with a diameter of about 0.5 μm.
Institute for Systems Biology
According to lead researcher, Professor Petra Levin: “Triclosan increased the number of surviving bacterial cells substantially. Normally, one in a million cells survive antibiotics, and a functioning immune system can control them. But triclosan was shifting the number of cells. Instead of only one in a million bacteria surviving, one in 10 organisms survived after 20 hours. Now, the immune system is overwhelmed.”
This indicates that triclosan imparts a protective mechanism to pathogenic bacteria, enabling them to become resistant to antibiotic treatment. This was demonstrated using several antibiotics and the common urinary tract pathogen Escherichia coli.
In terms of the mechanism at play, the researchers found that triclosan works in conjunction with a cell growth inhibitor, a small molecule termed ppGpp. This dual action renders bacterial cells less sensitive to antibiotics.
Research paper
The research has been published in the journal Antimicrobial Agents and Chemotherapy. The research paper is titled “The widely used antimicrobial triclosan induces high levels of antibiotic tolerance in vitro and reduces antibiotic efficacy up to 100-fold in vivo.”
Essential Science
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This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week we investigated a new technology that can convert plastic waste (the biggest environmental issue associated with modern society) into a clean fuel. This represents one useful application to address the global plastic crisis.
The week before, we marked the 150th anniversary of the periodic table of elements, and weighed in on the discussion about how big the table might become.
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