A Transformative Technology Platform for Interrogating Airborne Adaptation of Respiratory Pathogens

Aerosols are everywhere in the atmosphere, ranging in size from the very small nanometre-sized particles produced by cars through to larger water droplets in clouds with diameters similar to that of a human hair. Not only can pollution particles lead to increased rates of morbidity and mortality, but they can also act as a means of transporting bacteria and viruses, facilitating disease transmission. Indeed, infectious diseases are spread by the airborne route through aerosol droplets produced by the human body and expelled through coughing and sneezing. Such events account for some of the deadliest infectious diseases, including tuberculosis (TB), severe acute respiratory syndrome (SARS) and bacterial meningitis, all of which have a major impact on our society. Despite the significant health and financial burdens that arise from the airborne transmission of pathogens, studying bacteria and viruses in the aerosol phase remains challenging as few measurement techniques exist to explore the changes in viability and infectivity that may occur during airborne transport.

In the proposed research, we will develop a novel instrument for exploring the processes that affect how well bacteria survive when in airborne droplets. In particular, we will build and test an instrument that will allow the suspension and manipulation of aerosol particles in air containing a known number of bacteria. For example, we will develop an approach to generate individual droplets that mimic our coughs and sneezes, each containing a known number of bacteria. By subtly manipulating each droplet, we will be able to catch and levitate them in an electric field for any amount of time. We will then, in a controlled way, deposit the droplets into a dish containing suitable conditions to allow any bacteria present to grow. Whilst airborne, we will be able to change the temperature and humidity of the environment experienced by the droplets. We will also expose them to light (similar to sunlight) and also to typical atmospheric chemicals like ozone. Combined, these capabilities will allow us to simulate the processes the bacteria experience whilst moving from person-to-person. Thus, we will be able to measure how different environmental conditions influence how many bacteria remain alive at different time points.

Once the instrument has been built and tested, we will study a bacterium (Neisseria meningitidis also known as meningococci) which causes blood and brain infections but can be spread from person to person by coughing and sneezing. We will measure the airborne survival of meningococci at different times, temperatures and humidities, with conditions representative of cold-wet or cold-dry environments to simulate winter day conditions typical of the UK, or hot-dry conditions typical of the Africa dry season. These conditions represent seasons when the disease rates are highest in both regions. Finally, we will combine droplet capture with an exciting new instrument, the NanoString, which can measure how bacteria change in ways which could make them more or less able to cause disease. Together, the capabilities to measure not only how long bacteria survive but how they change outside of our bodies will help us to use mathematics to better model risks of disease spread, and also to identify novel better means of preventing person-to-person infection by aerosol (airborne) transmission.

We propose to develop a technology platform for examining the processes that influence the airborne transmission of pathogens. Although known to be an important route of transmission for a number of communicable diseases including tuberculosis, severe acute respiratory syndrome and bacterial meningitis, the conventional techniques available for exploring the survival of bacteria while airborne are unable to answer important questions on what happens to the bacteria while airborne. For example, aerosols particles containing bacteria (e.g. from coughs and sneezes) undergo rapid changes in solute concentrations on transport, responding to environmental changes in relative humidity and temperature. They also have high surface-to-volume ratio, readily exposing the particles to their surrounding environment and are exposed to light and atmospheric oxidants.

Based on an established track record of developing novel instrumentation for aerosol microphysics, we propose an instrument that allows the capture of a cloud of aerosol droplets with a known population each containing a known number of bacteria. The aerosol cloud can be levitated for an indefinite timeframe and exposed to conditions that represent the atmosphere. At a well-defined time, they can be deposited directly into a growth medium and the number of culture forming units determined. The decay in viability of the bacteria can be explored with varying environmental processing.

Early work-packages will concentrate on the development of the new instrument for levitating particles containing respiratory pathogens and simulating environmental conditions. Benchmarking will explore the reproducibility of measuring the viability of the category 2 pathogen Neisseria meningitidis with varying relative humidity, temperature, light and oxidant concentration. Finally, we explore the feasibility of combining the new technology with a NanoString to examine the transcriptomic response of aerosolised pathogens.

We propose the development of a novel technology platform for examining the processes that lead to the airborne transmission of pathogens, examining directly the interplay of the chemical, physical, biological and environmental factors that influence microbial survival while airborne. Unlike conventional techniques (which are mostly based on mid-20th century technology, the Goldberg drum for levitation of large samples of aerosols), our approach will have a significant impact by achieving a paradigm shift in measurement capability. We will provide a much-needed new technology that allows complete control of the aerosol composition, the use of microliter samples, the controlled exposure of the airborne pathogens to environmental conditions for a precise period of time and routine sampling and analysis.

The airborne spread of disease is an important transmission route for many of the deadliest communicable diseases and is a significant cause of morbidity worldwide. Examples with a major social and economic impact spread by airborne transmission include tuberculosis, severe acute respiratory syndrome and bacterial meningitis. Tuberculosis was estimated to have killed 1.6 million people in 2017 and, according to the WHO, has a global cost of $21 billion each year. In 2002-2003, SARS killed over 700 people and spread into 37 countries with a cost of $18 billion in Asia. In the USA there are around 4000 cases and 500 deaths due to bacterial meningitis per annum; in Africa, case numbers can be as high as 1000 per 100,000 population.

Pathogens are dispersed in aerosol particles through, for example, coughs and sneezes. However, despite the importance of such airborne routes of transmission, the interplay of the chemical, physical, biological and environmental factors that influence microbial survival and the expression of factors which aid colonisation and disease whilst airborne are poorly understood. Our proposed instrument for the improved characterisation of pathogens while airborne could help develop strategies to mitigate and treat the spread of respiratory pathogens, reducing their impact on our health. Understanding the phenotypic differences displayed by airborne organisms could better inform vaccine design, infection control procedures, and epidemiological modelling. It could facilitate the rational design of drugs or strategies (e.g. heating and air conditioning usage in public spaces) to reduce the longevity of airborne organisms, thereby reducing their transmission rate.

Beyond these impacts, we will develop a prototype instrument in collaboration with Biral, a UK based SME manufacturing meteorological sensors and aerosol detectors. As in our previous collaboration to produce a commercial version of the aerosol optical tweezers, Biral will develop an instrument for broader use by the environmental and life sciences, having an impact on Biral and the broader aerobiology and aerosol community.

The research team will work closely with existing collaborators at national and governmental laboratories, including the Defence Science and Technology Laboratory, Public Health England and Pirbright, delivering new capabilities. Knowledge transfer to these collaborators and partners will catalyse new avenues of research allowing, for example, improved models of disease transmission following a security incident.

Following on from a very preliminary demonstration of the new capability for a non-respiratory pathogen, the Bristol team were interviewed by the BBC for the Radio 4 programme Inside Science. The team will work with the public engagement team at the University of Bristol to broaden the impact of the research into the public domain, with interesting and informative presentations on airborne transmission of disease by aerosols. Finally, the project will lead to a trained practitioner working at the interface of microbiology, aerosol science, environmental science and chemistry, a unique breadth of expertise.