What lies beneath
Forget what the ads for cleaning products would have us believe, bacterial micro-organisms are crucial for our wellbeing, writes MARIE BORAN
THE HUMAN BODY is a busy place teaming with alien life. Right now there are about 100 trillion micro-organisms inside you, tiny creatures that are living, dying, feeding, fighting, multiplying and happily occupying your inner space.
It is not one or two varieties but a whole host of organisms, known as microbes or micro-organisms to scientists but bugs to the rest of us.
“Microbes are virtually anything of microscopic size: parasites, moulds, yeast, and bacteria,” says Prof Colin Hill from the Alimentary Pharmabiotic Centre at University College Cork. “To date we’ve categorised over 2,000 of these wild and wonderful creatures that live in the average healthy human body.”
These microbes, mostly bacteria, are not harmful to the human body. In fact we enjoy a co-operative relationship with our native microbes. We provide them with a warm environment and food. In exchange they help us digest our food in order to absorb certain nutrients. “If you had no microbes you would be a very unhealthy individual. You wouldn’t be able to digest food and your immune system would be extremely weak. They live in harmony with us and with each other. One species can break down certain materials in the digestive tract and the other will harvest this.”
It’s not all harmony, however. There is a constant battle being waged inside all of us, says Dr Stephen Smith from Trinity College’s department of clinical microbiology.
“Thankfully most of us have a healthy immune system that protects us on a minute-by-minute basis. Every time we brush our teeth we introduce outside bacteria to the bloodstream but they are killed almost instantly.”
The immune system differenciates between friendly microbes, or “commensals”, and the disease-causing ones known as “pathogens”. Bacteria reside outside the protective layer of cells on the human body and once they start invading it sets off danger signals, says Smith.
Our body also naturally flushes out potentially dangerous microbes. This is one of the reasons we have tear ducts, explains Dr Conor O’Byrne from the Bacterial Stress Response Group at NUI Galway. “The surface of the eye is not a particularly great place for microbes to live because our tears contain antibacterial substances. Otherwise our eyes would become cloudy with bacterial growth.”
The importance of the good bacteria living inside us is highlighted when pathogenic bacteria make us ill. Many bacterial infections are treated by broad-spectrum antibiotics that kill the bad guys but a lot of the good guys too, says Dr Christine Loscher from the school of biotechnology at DCU.
“When you take these antibiotics orally they go straight into the gut. They tend to wipe out a lot of the friendly bacteria there. This is why many people experience cramping, digestive problems and suffer from diarrhoea afterwards.”
Not all good bacteria are wiped out and they rapidly multiply to repopulate your digestive system, Loscher says. “Dairy foods, especially yogurt, can help maintain the balance of good bacteria. This is something humans have been aware of on some level since ancient times. Fermented foods containing bacteria were eaten for this purpose.”
Modern science further understands the role that many of these microbes play in human health by profiling their DNA, the genetic material from which they are composed.
“Because of advancements like the Human Genome Project it has become easier to extract DNA from organisms. This is a bit like collecting evidence at a crime scene,” says Hill, explaining part of his work at the Pharmabiotic Centre. “If you want to examine bacteria from the gut or mouth you take a swab or a biopsy or perhaps scrape plaque off teeth. Putting it crudely what you then do is take the live sample, smash open the microbes, extract genetic material and sequence this to identify them.”
In the past microbial samples were placed separately on agar plates in a lab, but Hill says that this missed out on the complex interactions happening between different species. “These micro-organisms inside our bodies work together so when we separated them in the lab they didn’t grow.”
Microbiologists thought they had inner space figured out but were wrong, says Hill: “We thought we knew what was there but it was much more complicated than we expected. You could say microbiology has had a big shock over the last 10 to 15 years.”
One of the reasons for studying the behaviour of these microbes is that it could lead to the development of therapies or treatments, says Hill. These bacteria produce things and communicate with the immune system. “If we can extract these compounds and try to reproduce them in the lab maybe they can be used in development of new drugs.”
Despite all of this, bacteria get a lot of bad press, especially in commercials for cleaning products, says Prof Wim Meijer from the Conway Institute at UCD. “People don’t seem to realise that without microbes we wouldn’t even be here.”
Your body - a colony for trillions
IF YOU’RE ONE of those people who doesn’t like sharing your dessert keep this in mind next time a friend reaches over for a forkful. Each bite of chocolate cake you take is also being enjoyed by more than 100 trillion others, the microscopic life forms living happily in your gut.
Micro-organisms don’t just live in our digestive tract. They’re found in every nook and cranny of the human body from our eyelashes to between our toes. There are more than 2,000 known species and they have been colonising us from the moment we were born.
The vast majority of these microbes (more than 99 per cent) are strains of bacteria and most of these live somewhere in our digestive tract. There are also some viruses, fungi and protozoa too.
Overall there are thought to be about 1,000 different species present in the gut alone. They are so many microbial cells in the human body that they outnumber our own cells 10 to one.
“They’re everywhere. It doesn’t make a difference if you frequently wash your hands. The entire surface of your skin is teeming with them,” says Prof Wim Meijer from the Conway Institute of Biomolecular Biomedical Research at University College Dublin.
This does not mean that they pose a threat to our health. The opposite is true. “Our body’s native species are quite beneficial and provide us with certain vitamins and amino acids as well as forming a protective layer against disease-carrying micro-organisms,” he says.
“If you were somehow able to remove all of these microbes from the gut you would die rapidly and horribly,” Meijer points out.
We could theoretically survive without these co-operative micro-organisms if it were possible to live in a completely sterile, germ-free environment. This would bring on its own problems, however.
“The immune system would begin to misbehave and you would be hypersensitive to disease,” says Prof Colin Hill from the Alimentary Pharmabiotic Centre at University College Cork. “You’d also have to eat 50 per cent more food just to maintain energy because these microbes help us break down food and extract nutrients.”
Not all of our fellow travellers are harmless or beneficial, however.
“The most negative impact of microbes living in the oral cavity is the damage they cause to your teeth,” says Dr Conor O’Byrne from the Bacterial Stress Response Group at NUI Galway.
It’s not sugar that causes tooth decay. Bacteria love to “eat” sugar, producing tooth-unfriendly acids as a result, explains O’Byrne. The less sugar they find, the less acid is produced – another reason to share your dessert!