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UNSW Science microbiologists studied an E. coli strain that causes a severe intestinal infection in humans: enterohemorrhagic E. coli (EHEC). Their findings were published this week in the journal PNAS (Proceedings of the National Academy of Sciences).

EHEC is a food-borne pathogen that releases Shiga toxins during infection, resulting in kidney and neurological damage.

Dr Jai Tree, the study’s senior author, said the researchers’ discovery of a new molecular pathway that controls Shiga toxin production was important because there was no commercially available treatment for EHEC infections.

“Antibiotic treatment of these infections is generally not recommended because antibiotics stimulate production of the Shiga toxin, leading to an increased risk of kidney failure, neurological damage, and death,” Dr Tree said.

“The new pathway that we have found reduces toxin production and is not expected to be stimulated by antibiotic treatment. So, our results identify a potential new target for the development of drugs that can suppress Shiga toxin production during EHEC infection.

“It’s still early days, however, and we need to conduct a lot more research to understand if our findings apply to a broad range of clinical EHEC isolates and to both types of Shiga toxins produced by human EHEC isolates.”

The spider-like icosahedral shape is an abstract depiction of the Shiga toxin bacteriophage with a red genome, stylised as the puppet master of a potentially deadly EHEC infection. Image: UNSW Science

Dr Tree said there were several ways in which people could become infected with EHEC.

“EHEC is mainly found in the faeces of cows and sheep and people can become infected through contact with farm animals and their faeces, or via person-to-person infection if people come into contact with tiny amounts of faeces from a sick person – for example, directly or indirectly by touching contaminated surfaces,” he said.

“This strain of E. coli can also spread through ingesting the bacteria by eating undercooked minced meat (for example, in hamburgers), eating contaminated fresh produce like salad vegetables, or drinking contaminated water or unpasteurised milk.

“Children under five years old and older people are at greatest risk of developing an EHEC infection.”

Dr Tree said while the prevalence of EHEC was low compared to other foodborne pathogens, the disease could be very severe or even fatal. EHEC is a type of STEC (Shiga toxin-producing Escherichia coli).

“EHEC outbreaks occur sporadically in Australia and worldwide. The most significant outbreak occurred in South Australia in 1995 and was caused by contaminated mettwurst, a semi-dry fermented sausage made from raw minced pork preserved by curing and smoking,” he said.

“In that outbreak, 143 people were infected – 23 of them suffered kidney and neurological damage. Many of these severe cases were in infants who suffered permanent kidney damage and later required kidney transplants.

“A four-year-old girl suffered multiple strokes and died three days after admission to hospital. This episode triggered a major food safety investigation and outbreaks since 1995 have been smaller.”

Dr Tree said globally, Shiga toxin-producing E. coli was still a major food safety concern after a large outbreak in Germany in 2011.

“The strain in Germany was spread mostly via consumption of contaminated sprouts and in several cases, from close contact with an infected person,” he said.

“During this outbreak more than 4000 people were infected and 50 people died.”

Dr Tree said the UNSW research was the first discovery of a new pathway that controls the Shiga toxins in almost 20 years.

“In 2001, researchers at Tufts and Harvard universities first showed how production of the Shiga toxin was controlled by a bacterial virus, known as a bacteriophage, within the genome. This has been the only known pathway that controls Shiga toxin production for almost two decades,” he said.

“We have extended that work to show a new mechanism of toxin control that is, surprisingly, buried within the start of the DNA sequence that encodes the Shiga-toxin messenger RNA – a working copy of the gene.

“We discovered a very short piece of the toxin messenger RNA is made into a regulatory non-coding RNA that silences the toxin and promotes growth of the pathogen.”

Dr Tree said their findings were a surprise because Shiga toxin genes have been well studied, with almost 7000 published studies in the past 40 years.

“Only recently have we been able use advances in RNA sequencing technology to detect the presence of the new regulatory non-coding RNA embedded within the Shiga toxin messenger RNA,” he said.

“This new regulatory non-coding RNA had been hiding in plain sight for almost 20 years.”

Dr Tree said the researchers’ findings opened up new possibilities for the treatment of EHEC infections.

“Patients largely receive supportive care to manage disease symptoms and to reduce the effects of the toxin on the kidneys,” he said.

“Our work shows a new mechanism for controlling toxin production that may be amenable to new RNA-based therapeutics to inhibit toxin production during an infection. We anticipate this would expand intervention options and potentially allow use of antibiotics that are currently not recommended because they stimulate Shiga toxin production.

“New treatments could therefore reduce the risk of kidney damage, neurological complications and death. We look forward to testing these new interventions in the next stage of our research.”

Find the study in PNAS: https://doi.org/10.1073/pnas.2006730117 

The new device is not technically a turbine. It is a nanogenerator made of two plastic strips in a tube that flutter or clap together when there is airflow. Like rubbing a balloon to your hair, the two plastics become electrically charged after being separated from contact, a phenomenon called the triboelectric effect. But instead of making your hair stand up like Einstein's, the electricity generated by the two plastic strips is captured and stored.

"You can collect all the breeze in your everyday life," says senior author Ya Yang of Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences. "We once placed our nanogenerator on a person's arm, and a swinging arm's airflow was enough to generate power."

A breeze as gentle as 1.6 m/s (3.6 mph) was enough to power the triboelectric nanogenerator designed by Yang and his colleagues. The nanogenerator performs at its best when wind velocity is between 4 to 8 m/s (8.9 to 17.9 mph), a speed that allows the two plastic strips to flutter in sync. The device also has a high wind-to-energy conversion efficiency of 3.23%, a value that exceeds previously reported performances on wind energy scavenging. Currently, the research team's device can power up 100 LED lights and temperature sensors.

"Our intention isn't to replace existing wind power generation technology. Our goal is to solve the issues that the traditional wind turbines can't solve," says Yang. "Unlike wind turbines that use coils and magnets, where the costs are fixed, we can pick and choose low-cost materials for our device. Our device can also be safely applied to nature reserves or cities because it doesn't have the rotating structures."

Yang says he has two visions for the project's next steps: one small and one big. In the past, Yang and his colleagues have designed a nanogenerator as small as a coin, but he wants to make it even tinier and more compact with higher efficiency. In the future, Yang and his colleagues would like to combine the device to small electronic devices such as phones, to provide sustainable electric power.

But Yang is also looking to make the device bigger and more powerful. "I'm hoping to scale up the device to produce 1,000 watts, so it's competitive with traditional wind turbines," he says. "We can place these devices where traditional wind turbines can't reach. We can put it in the mountains or on the top of buildings for sustainable energy."

Xin Chen, Xingchen Ma, Weiwei Ren, Lingxiao Gao, Shan Lu, Daqiao Tong, Fayang Wang, Yu Chen, Yi Huang, Hao He, Baoping Tang, Jiajia Zhang, Xiaoqing Zhang, Xiaojing Mu, Ya Yang. A Triboelectric Nanogenerator Exploiting the Bernoulli Effect for Scavenging Wind Energy. Cell Reports Physical Science, 2020; 1 (9): 100207 DOI: 10.1016/j.xcrp.2020.100207