How can we reduce the public health burden of food and waterborne diseases?


While some bacteria are beneficial, such as probiotic bacteria in the human gastrointestinal tract, others can have serious consequences for human health.


Professor Aliyar Cyrus Fouladkhah of  Tennessee State University  studies preventative measures for microbial pathogens and foodborne and waterborne infectious diseases in the context of climate change.


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Hello and welcome to Research Pod! Thank you for listening and joining us today.


In this episode, we will be looking at the research of Professor Aliyar Cyrus Fouladkhah of the Public Health Microbiology Laboratory at Tennessee State University, USA. Professor Fouladkhah and his team explore novel interventions against food and waterborne infectious diseases.


Microbial life – including bacteria, fungi, and viruses – has been present on Earth for around 3.5 billion years, vastly preceding the emergence of humans some 300,000 years ago. Part of the reason these organisms are so successful is how they use their genetic material. Bacteria have evolved to overcome new challenges and encourage diversity and fitness, meaning the ability to adapt, survive, and outcompete other strains of bacteria within an environment. One example of these mechanisms is binary fission, which allows one bacterium to multiply into two bacteria. In some cases, this takes as little as 20 minutes. This means that under optimal conditions, a single bacterium is able to multiply to over 50 billion bacteria in the space of 24 hours.


While some bacteria are beneficial, such as probiotic bacteria that are part of the microbial ecosystem in the human gastrointestinal tract, others can have serious consequences for human health and diseases.


Due to their rapid replication rate and their ability to survive in otherwise unhospitable conditions, microbial pathogens present a major public health concern. Already, the World Health Organization estimates that 420,000 individuals die each year due to infections associated with contaminated foods globally, and a further 2 million deaths are due to waterborne diarrhoeal diseases.

Professor Aliyar Fouladkhah, faculty director of the Public Health Microbiology Laboratory at Tennessee State University, studies how foodborne and waterborne bacteria can cause diseases and survive in challenging environments. Once we understand the techniques bacteria use to survive, we can develop novel decontamination treatments to reduce the public health burden of these infectious diseases.


Bacteria are constantly finding new ways to push back against existing medications, meaning that when a new therapy is used, the bacteria might have already started to develop resistance. Therefore, researchers must stay one step ahead and consider more novel therapeutic approaches.


Climate change is augmenting the spread and proliferation of microbial pathogens and infectious diseases. Fouladkhah explains that while it can be difficult to predict the impact of a changing climate on infectious diseases, it is well established that increases in environmental temperatures lead to proliferation of bacteria that can cause infectious diseases. For example, a 1oC rise in temperature may lead to a 5 to 10% increase in salmonellosis, an illness caused by Salmonella bacteria. This could equate to an additional 50,000 to 100,000 cases of foodborne salmonellosis each year in the US alone.


Fouladkhah highlights that we need new approaches that consider the impact of climate change on antibiotic resistance and infectious diseases. He also explains that it is not just foodborne pathogens that should be considered. Increased rainfall, coupled with changes in the environment due to climate change, may contribute to higher multiplication rates of algae and the spread of various waterborne infectious diseases.


Bacteria are able to form complex structures or communities called ‘biofilms’. An example of this is the build-up of bacteria on teeth that forms dental plaques. Within biofilm colonies, the bacteria could communicate with each other and with bacteria outside the biofilm through a process called quorum sensing. Quorum sensing provides bacteria with the advantage of passing on messages. If one bacterium obtains genetic changes that allow it to become resistant to a drug, it can spread changes in gene regulation throughout the whole colony. This has obvious benefits for bacteria, but it also offers an attractive therapeutic target: disrupting this communication pathway could make bacteria vulnerable to antimicrobial treatments.


Biofilms also help the bacteria to be resistant to some interventions, including the use of antibacterial agents that are used in food and drink manufacturing. Fouladkhah has previously explored the effectiveness of substances such as sodium hypochlorite against different biofilms. The study results showed that sodium hypochlorite was unable to completely eliminate biofilms that were 1–2 weeks old. As a result, decontamination strategies may be less effective than previously thought.


Bacteria such as Cronobacter sakazakii can survive in dry environments, such as powdered infant formula, and cause fatal infections for premature or newborn infants. Fouladkhah explains that interventions are required to minimise the risk of contamination during the manufacturing of infant formulas. These include existing practices, such as regular sampling and testing for contamination and ensuring that caregivers follow instructions when preparing infant formula. More novel techniques include the use of high-pressure processing.


Bacterial infections are responsible for the vast majority of foodborne hospitalizations and deaths. The most common pathogens include Shiga toxin-producing Escherichia coli, typhoidal and non-typhoidal strains of Salmonella, Listeria monocytogenes, and pathogenic species of Cronobacter. All these bacteria can form biofilms, so improper cleaning of surfaces that come into contact with food can contribute to foodborne diseases. Fouladkhah compared biofilm formation by E. coli and Salmonella and the response to changes in temperature and exposure to different antimicrobials. The researcher found that increased temperatures caused enhanced biofilm production, and bacteria were more likely to survive after sanitation if they had been exposed to higher temperatures. This may indicate the need for different sanitation protocols for different environmental conditions.


In addition to foodborne diseases, bacteria can also cause waterborne diseases. Perhaps the most well-known example is the outbreak of cholera, caused by a bacterium called Vibrio cholerae. Today, waterborne diseases tend to be most commonly associated with many of the same bacteria that cause foodborne illness, such as Salmonella, L. monocytogene, and Shiga toxin-producing E. coli.

In particular, this is due to their ability to survive and develop biofilms. The researchers at Tennessee State University’s Public Health Microbiology laboratory explored this further by investigating how well these bacteria survived in surface water stored at different temperatures. They found that all three pathogens demonstrated similar survival abilities, with Salmonella having the best chance for survival. This has important implications for public health and food processing as it suggests that these bacteria are able to persist for an extended period of time, even in unfavourable and low-nutrient conditions.


Due to their ability to survive many current decontamination approaches, there is a need for new and emerging technologies to reduce the public health burden of food and waterborne infectious diseases. One way this could be achieved is through hydrostatic processing of food products.


Traditional food processing methods that use high temperatures to inactivate microorganisms can impact the quality of the resulting food product. However, the use of non-thermal elevated hydrostatic pressure may offer an attractive alternative. This approach involves applying very high pressures to foods, around 600 megapascal or 87 kilo-pounds per square inch for under 10 minutes. High-pressure processing techniques are already used for many products, but this approach can be expensive. Therefore, it may be possible to use slightly lower pressures and still see the beneficial effects. A study done by Fouladkhah and colleagues used mild heat and pressure-based pasteurisation methods for milk and orange juice. It was able to show that using mild heat alongside pressure-based treatments provided the best results.


Given the rise of antibiotic resistance and the impact of climate change on bacterial survival and proliferation, there is a need to develop new preventative measures. Fouladkhah proposes that this could be done by implementing a combination of epidemiological tools and laboratory technologies, such as genetic sequencing of bacteria. Whole genome sequencing techniques allow scientists to quickly detect and characterise outbreaks of infectious diseases. Using new technologies and therapies will help to mitigate some of the impacts of climate change on infectious diseases, but ultimately preventing future outbreaks may be avoided in some part by taking action to reduce our impact on the environment.


That’s all for this episode – thanks for listening, and stay subscribed to Research Pod for more of the latest science. See you again soon.

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