Triclosan, often maligned, may have a good side — treating cystic fibrosis infections

By Chris Waters

Maybe you’ve had the experience of wading in a stream and struggling to keep your balance on the slick rocks, or forgetting to brush your teeth in the morning and feeling a slimy coating in your mouth. These are examples of bacterial biofilms that are found anywhere a surface is exposed to bacteria in a moist environment.

Besides leading to falls in streams or creating unhealthy teeth, biofilms can cause large problems when they infect people. Biofilms, multicellular communities of bacteria that can grow on a surface encased in their own self-produced matrix of slime, can block immune cells from engulfing and killing the bacteria or prevent antibodies from binding to their surface.

On top of this, bacteria in a biofilm resist being killed by antibiotics due to the sticky nature of the matrix and activation of inherent resistant mechanisms, such as slow-growing cells or the ability to pump antibiotics out of the cell.

Biofilms are one of the primary growth modes of bacteria, but all antibiotics currently used clinically were developed against free-swimming planktonic bacteria. This is why they do not work well against biofilms.

My laboratory studies how and why bacteria make biofilms, and we develop new therapeutics to target them. Because antibiotic resistance is the most problematic aspect of biofilms during infections, we set out to identify novel molecules that could enhance antibiotic activity against these communities.

We discovered that an antimicrobial that has recently obtained a bad reputation for overuse in many household products could be the secret sauce to kill biofilms.

The hunt for antibiotic superchargers

To find such compounds, we developed an assay to grow plates of 384 tiny biofilms of the bacterium Pseudomonas aeruginosa. We did this to screen for molecules that enhance killing by the antibiotic tobramycin. We chose this bacterium and this antibiotic as our test subjects because they are commonly associated with cystic fibrosis lung infections and treatment.

People with cystic fibrosis (CF) are at particular risk from biofilm-based infections. These infections often become chronic in the lungs of cystic fibrosis patients and are often never cleared, even with aggressive antibiotic therapy.

After we screened 6,080 small molecules in the presence of tobramycin, we found multiple compounds that showed the antibiotic enhancement activity we were searching for. Of particular interest was the antimicrobial triclosan because it has been widely used in household products like toothpaste, soaps and hand sanitizers for decades, indicating that it had potential to be safely used in CF patients. Triclosan has also garnered a bad reputation due to its overuse, and states like Minnesota have banned it from these products. The Food and Drug Administration banned its use from hand soaps in September 2016. This ruling was not based on safety concerns, but rather because the companies that made these products did not demonstrate higher microbial killing when triclosan was added, compared to the base products alone.

Another fact that piqued our interest is that P. aeruginosa is resistant to triclosan. Indeed, treatment with either tobramycin or triclosan alone had very little activity against P. aeruginosa biofilms, but we found that the combination was 100 times more active, killing over 99 percent of the bacteria.

We further studied this combination and found that it worked against P. aeruginosa and other bacterial species that had been isolated from the lungs of CF patients. The combination also significantly enhanced the speed of killing so that at two hours of treatment, virtually all of the biofilm is eradicated.

Our efforts are now focused on pre-clinical development of the tobramycin-triclosan combination. For CF, we envision patients will inhale these antimicrobials as a combination therapy, but it could also be used for other applications such as diabetic non-healing wounds.

Although questions about the safety of triclosan have emerged in the mainstream media, there are actually dozens of studies, including in humans, concluding that it is well tolerated, summarized in this extensive EU report from 2009. My laboratory completely agrees that triclosan has been significantly overused, and it should be reserved to combat life-threatening infections.

The next steps for development are to initiate safety, efficacy and pharmacological studies. And thus far, our own studies indicate that triclosan is well tolerated when directly administered to the lungs. We hope that in the near future we will have enough data to initiate clinical trials with the FDA to test the activity of this combination in people afflicted with biofilm-based infections.

We think our approach of enhancing biofilm activity with the addition of novel compounds will increase the usefulness of currently used antibiotics. Learning about how these compounds work will also shed light on how bacterial biofilms resist antibiotic therapy.

Original article here.

Toothpaste ingredient may bust up cystic fibrosis biofilms

By Chris Waters and Sarina Gleason

A common antibacterial substance in toothpaste may combat life-threatening diseases such as cystic fibrosis when combined with an with an FDA-approved drug, researchers report.

Researchers have found that when triclosan, a substance that reduces or prevents bacteria from growing, combines with an antibiotic called tobramycin, it kills the cells that protect the CF bacteria, known as Pseudomonas aeruginosa, by up to 99.9 percent.

CF is a common genetic disease with one in every 2,500 to 3,500 people diagnosed with it at an early age. It results in a thick mucus in the lungs, which becomes a magnet for bacteria.

These bacteria are notoriously difficult to kill because a slimy barrier known as a biofilm, which allows the disease to thrive even when treated with antibiotics, protects them.

“The problem that we’re really tackling is finding ways to kill these biofilms,” says Chris Waters, lead author of the study and a microbiology professor at Michigan State University.

According to Waters, there are many common biofilm-related infections that people get, including ear infections and swollen, painful gums caused by gingivitis. But more serious, potentially fatal diseases join the ranks of CF including endocarditis, or inflammation of the heart, as well as infections from artificial hip and pacemaker implants.

Waters and his coauthors grew 6,000 biofilms in petri dishes, added in tobramycin along with many different compounds, to see what worked better at killing the bacteria. Twenty-five potential compounds were effective, but one stood out.

“It’s well known that triclosan, when used by itself, isn’t effective at killing Pseudomonas aeruginosa,” says coauthor Alessandra Hunt, a postdoctoral associate of microbiology and molecular genetics. “But when I saw it listed as a possible compound to use with tobramycin, I was intrigued. We found triclosan was the one that worked every time.”

Triclosan has been used for more than 40 years in soaps, makeup, and other commercial products because of its antibacterial properties. Recently, the FDA ruled to limit its use in soaps and hand sanitizers due to insufficient data on its increased effectiveness and concern about overuse. Clear evidence has shown, though, that its use in toothpaste is safe and highly effective in fighting gingivitis, and it is still approved for use.

“Limiting its use is the right thing to do,” says coauthor Michael Maiden, a graduate student in medicine. “The key is to avoid creating resistance to a substance so when it’s found in numerous products, the chances of that happening increase.”

Tobramycin is currently the most widely used treatment for CF, but it typically doesn’t clear the lungs of infection, Waters says. Patients typically inhale the drug, yet still find themselves chronically infected their whole lives, eventually needing a lung transplant.

“Most transplants aren’t a viable option though for these patients and those who do have a transplant see a 50 percent failure rate within five years,” he says. “The other issue is that tobramycin can be toxic itself.” Known side effects from the drug include kidney toxicity and hearing loss.

“Our triclosan finding gives doctors another potential option and allows them to use significantly less of the tobramycin in treatment, potentially reducing its use by 100 times,” Hunt says.

Within the next year, Waters and his colleagues will begin testing the effectiveness of the combination therapy on mice with hopes of it heading to a human trial soon after since both drugs are already FDA approved.

Just brushing your teeth with toothpaste that has triclosan won’t help to treat lung infections though, Maiden says.

“We’re working to get this potential therapy approved so we can provide a new treatment option for CF patients, as well as treat other biofilm infections that are now untreatable. We think this can save lives,” he says.

The research appears in the journal Antimicrobial Agents and Chemotherapy.

The National Institutes of Health, Cystic Fibrosis Foundation, and Hunt for a Cure in Grand Rapids, Michigan funded the research.

Source: Michigan State University

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