Navigating our microbial world: the good, the bad, and the role of hygiene

​​News | 3 January 20​​​​​24

It is estimated that there are one trillion different microbial species on earth. These bacteria, fungi, viruses, and algae inhabit just about every part of the globe, from the icecaps of the Antarctic to the hot springs of Yellowstone Park. We too provide an excellent environment for microorganisms to thrive, and it is believed that the human body is home to as many bacterial cells as human cells. Microbes are all around us, on us and in us, but to borrow a well-known motto written in big friendly letters – “Don’t Panic”.

Life on earth is dependent on our co-habiting microorganisms. Without them, we would not have an oxygen atmosphere, we would have no carbon or nitrogen cycle, dead plants and animals would not decompose, and we would not enjoy delights such as cheese, wine, bread, and the many other fermented foods we consume. From a more personal perspective, the microbes that call us home are of huge benefit and we could not function properly without them. For example, the bacteria in our gut help to digest food and some of them produce key vitamins and amino acids that the human body cannot produce itself.

It is true that not all microorganisms are “good”, and the recent ​COVID pandemic has never made this more apparent. The so called “bad” microorganisms are referred to as pathogens and ​​cause symptoms of infectious disease. Of the 33,500 described bacterial species 7% are known to cause infectious disease, which is a very small proportion. However, these pathogens can cause some serious infectious diseases, so how do we protect ourselves and others?

You only have to watch a handful of adverts to see the multitude of products from mouthwash, detergent, hand soap, and disinfectants to get the impression that these items will solve all our problems by killing “99.9% of all known germs”. But do they? And do we need them to? These claims are not drawn from scientific evidence per se but are marketing language that satisfies a legal framework for the sale of these goods. Generally, products are tested against a small panel of bacteria, perhaps 3-4, that are representative of common types of pathogens and not the global population of microorganisms or indeed all known pathogens.

​Importantly, let’s consider whether it is necessary or prudent to live in a world devoid of 99.9% of all known germs. In the last century a surge in allergies led to the hygiene hypothesis of 1989 describing how living in an environment that is too clean is detrimental for proper immune development. Having since been dispelled there has been a shift towards understanding the difference between hygiene and infectious disease prevention. However, there is a distinct difference between personal hygiene which is about keeping yourself and your environment clean, and hygiene as defined by the World Health Organisation, referring to practices that preserve health and prevent the spread of infectious disease.

Personal hygiene is very much that – ​there are no scientific guidelines to underpin how often you should wash. Normal bacteria on the skin are responsible for the bad odours associated with sweat but are not a concern with regards to infectious disease transmission. However, practices such as handwashing after using the toilet, or covering your mouth when coughing or sneezing are crucial to prevent the spread of infectious diseases. During the COVID pandemic extra-efforts were made to encourage handwashing and wear facemasks to stop the spread of infection. Interestingly, the incidence rate of other infectious diseases, especially those spread by respiratory droplets, decreased as a side effect of these measures. So, the old adage “Coughs and Sneezes Spread Diseases” certainly still holds true today, even despite the advances made in medicines to control infection.

Although microorganisms are all around us, it is imperative to remember that while the majority are harmless, hygiene practices do have a role in preventing the transmission of infectious disease. Importantly, good habits such as handwashing and controlling respiratory droplet spread go some way to protecting vulnerable individuals and helps to conserve antibiotics. To learn more, listen to BBC Radio 4 Inside Health, airing on 9 January 2024.

Dr Sarah E. Hooper; Reader in Microbiology & Infection