Research opens possibility of reducing risk of gut bacterial infections with next-generation probiotic

A team of researchers is exploring the possibility that next-generation probiotics – live bacteria that are good for your health – would reduce the risk of infection with the bacterium Clostridium difficile. In laboratory-grown bacterial communities, the researchers determined that, when supplied with glycerol, the probiotic Lactobacillus reuteri produced reuterin, an antibacterial compound that selectively killed C. difficile. The study appears in Infection and Immunity.

C. difficile causes thousands of deaths and billions of dollars in healthcare expenses in the U.S. each year. Although most patients respond to antibiotic treatment, up to 35 percent will relapse and require extended antibiotic treatments,” said first and corresponding author Dr. Jennifer K. Spinler, instructor of pathology & immunology at Baylor College of Medicine, who oversees microbial genetics and genomics efforts at the Texas Children’s Microbiome Center at Texas Children’s Hospital.

C. difficile infections are the most common cause of diarrhea associated with the use of antibiotics. If these bacteria attempt to invade the human gut, the ‘good bacteria,’ which outnumber C. difficile, usually prevent them from growing. However, when a person takes antibiotics, for example to treat pneumonia, the antibiotic also can kill the good bacteria in the gut, opening an opportunity for C. difficile to thrive into a potentially life-threatening infection.

“When repeated antibiotic treatments fail to eliminate C. difficile infections, some patients are resorting to fecal microbiome transplant – the transfer of fecal matter from a healthy donor – which treats the disease but also could have negative side effects,” Spinler said. “We wanted to find an alternative treatment, a prophylactic strategy based on probiotics that could help prevent C. difficile from thriving in the first place.”

“Probiotics are commonly used to treat a range of human diseases, yet clinical studies are generally fraught by variable clinical outcomes and protective mechanisms are poorly understood in patients. This study provides important clues on why clinical efficacy may be seen in some patients treated with one probiotic bacterium but not with others,” said senior author Dr. Tor Savidge, associate professor of pathology & immunology and of pediatrics at Baylor and the Texas Children’s Microbiome Center.

Working in the Texas Children’s Microbiome Center, Spinler and her colleagues tested the possibility that probiotic L. reuteri, which is known to produce antibacterial compounds, could help prevent C. difficile from establishing a microbial community in lab cultures.

An unexpected result with major implications for a preventative strategy

Spinler and Savidge established a collaboration with co-author Dr. Robert A. Britton, professor of molecular virology and microbiology at Baylor and member of the Dan L Duncan Comprehensive Cancer Center.

The Britton lab uses mini-bioreactor arrays – multiple small culture chambers – that provide a platform in which researchers could recreate the invasion of an antibiotic-treated human intestinal community by C. difficile.

“Using the mini-bioreactors model we showed that L. reuteri reduced the burden of C. difficile infection in a complex gut community,” Britton said. “To achieve its beneficial effect, L. reuteri requires glycerol and converts it into the antimicrobial reuterin.”

The literature reports reuterin as a broad-spectrum antibiotic; it affects the growth of a wide variety of bacteria when they are tested individually in the lab. What was intriguing in this study is that reuterin didn’t have a broad-spectrum effect in the mini-bioreactor bacterial community setting.

“I expected reuterin to have an antibacterial effect on several different types of bacteria in the community, but it only affected C. difficile and not the good bacteria, which was exciting because it has major implications for a preventative strategy,” Spinler said.

“Although these results are too preliminary to be translated directly into human therapy, they provide a foundation upon which to further develop treatments based on co-administration of L. reuteri and glycerol to prevent C. difficile infection,” said co-author Dr. Jennifer Auchtung, director of the Cultivation Core at Baylor’s Alkek Center for Metagenomics and Microbiome Research and assistant professor of molecular virology and microbiology at Baylor.

In the future, this potential treatment could be administered prophylactically to patients before they take antibiotics known to disrupt normal gut microbes. The L. reuteri/glycerol formulation would help maintain the healthy gut microbial community and also help prevent the growth of C. difficile, which would result in decreased hospital stay and costs and reduced long-term health consequences of C. difficile recurrent infections.

How Do You Kill a Malaria Parasite? Clog It with Cholesterol

Drexel University scientists have discovered an unusual mechanism for how two new antimalarial drugs operate: They give the parasite’s skin a boost in cholesterol, making it unable to traverse the narrow labyrinths of the human bloodstream. The drugs also seem to trick the parasite into reproducing prematurely.

Malaria is a mosquito-borne disease caused by Plasmodium parasites. After a person is bitten, the parasite invades the victim’s red blood cells. There, it eventually divides into daughter parasites, which continue to destroy each red blood cell they infect.

There are several drugs under development that interrupt this life cycle, including a class of compounds discovered in 2014 by Akhil Vaidya, PhD, a professor at Drexel University College of Medicine. In their 2014 study, Vaidya and his research team found that these drugs increase levels of sodium within the parasites’ cells, causing them to swell and erupt.

However, in a new study, published recently in PLOS Pathogens, the researchers have revealed that this sodium increase actually triggers a more complex cascade of events, eventually changing the parasite’s outer membrane and also tricking it into early reproduction, which renders the parasite inert.

“Nobody suspected something like this to be the mode of action,” said Vaidya, who also directs Drexel’s Center for Molecular Parasitology. “The mechanism is a lot more complicated and interesting than we originally thought.”

In this study, the scientists focused on two small-molecule drugs, one of which is undergoing clinical trials. Despite very different molecular structures, both drugs initially increase sodium within the parasite and subsequently kill the pathogen. Until now, scientists have not understood why the increase in sodium concentration leads to the malaria parasite’s demise.

To explore this question, the researchers first tested the properties of the Plasmodium plasma membrane — or the parasite’s outer skin — before and after exposure to antimalarial drugs. The Plasmodium membrane is unusual, because it contains very low levels of cholesterol, a major lipid component of most other membranes, including those of human red blood cells.

The Drexel scientists hypothesized that the low cholesterol content permits greater flexibility for the parasite to travel through the human bloodstream and to withstand the stress of blood circulation. They propose that the sodium increase, caused by the antimalarial drugs, somehow interferes with that elasticity.

The researchers used a cholesterol-dependent detergent to detect the presence of lipids in the parasite membrane. They found that indeed both drug treatments appeared to add a significant amount of cholesterol to the Plasmodium plasma membrane.

“We believe that the cholesterol makes the parasite rigid, and then the parasite can no longer pass through very small spaces in the bloodstream,” Vaidya said, adding that the parasite cannot continue its lifecycle if it cannot enter red blood cells.

Just two hours after treatment, the scientists also saw that many of the parasites showed fragmented nuclei and interior membranes, which are the precursors to cell division. But these changes happened without any sign that the parasite’s genome had multiplied — a step that is necessary for a cell to divide and survive.

The researchers hypothesize that sodium influx is a normal step during the malaria parasite’s division. The antimalarial drugs prematurely induce this signaling event, and the parasite begins dividing before it should.

“The parasite is not ready to divide yet, so it can not survive. It is like premature delivery of an infant,” Vaidya said. “This whole cascade of events is triggered by these drug treatments.”

Malaria is the world’s deadliest parasitic disease. It kills more than 300,000 people per year, according to the World Health Organization, and affects up to 300 million.

One of the biggest challenges for treating malaria is drug resistance. The drugs that are currently available are quickly losing their potency, so researchers are scrambling to develop stronger treatments.

By understanding exactly how new drug candidates stop malaria, Vaidya and his team aim to reveal more about the parasite’s vulnerabilities. This, they hope, will eventually lead to the creation of more effective drugs against the disease. Vaidya noted that the best defense against malaria will always be a combination of treatments.