Senior students of biology will be familiar with the ‘Tree of Life’ diagram that accompanies this article. Based on Darwin’s Theory of Evolution, it shows the three major categories of living things in the form of a tree – a central trunk and three branches called Bacteria, Archaea and Eucharyotes respectively. A look at the diagram will show that ‘animals’ – and that includes us humans — are perched on the Eucharyote branch, and constitute but one of the several sub-branches, among which we find ‘plants’ as well. As can be seen, we are vastly outnumbered by all the other branches and sub-branches, representing organisms other than plants and animals, which are mostly microbes, that is cannot be seen by the naked eye and require the use of a microscope to be visible.
Microbes outnumber humans
We, human beings, are but a tiny speck in the giga-ocean of microbes. We live in that ocean as much as the microbes also live in and on us. We are just over 7 billion, and we are expected to stabilize at around 9 billion people on the planet eventually. But the microbes are in astronomical trillions, and new ones continue to be discovered. In fact, a thousand new types of bacteria that have been discovered over the past few years have led scientists to design a new ‘Tree of Life’, a news that was announced a couple of days ago by a team from the University of Berkeley in California. Reading up about that is what led me to some reflections about these microscopic life forms that we had studied in high school and at university, and at medical college there less in a global and holistic perspective than from the point of view of their nuisance value as disease-causing organisms.
In fact, until recently biologists have defined the interactions of plants and animals with the microbial world mostly in the context of disease states which are of more immediate concern to us. But we forget that the majority of these trillions of microbes are generally non-pathogenic, that is, they do not cause disease. On the contrary, they live in harmony and in symbiosis (deriving mutual benefit) with their hosts, and the human body is host to many such microbes – we are allies, what!
Perhaps this should not surprise because after all microbes have been around millions of years before we appeared on earth, and we have been associated with them, co-evolving, ever since we came on the scene. We are made up of common molecules, and share the characteristic called life with them, and believe it or not they are as alive as we are, albeit in their own way. They antedate us on this planet, and there is no reason to doubt that this is so too in the universe if we were to discover life ‘out there’. We evolved along with them, mutually coexisting and integrating with them in the long march of evolution. We are indeed relatives and friends or allies, but also at times enemies that fight deadly battles – in which, at the end of the day, they are the winners, although we may temporarily claim victory, as when we get cured of an infection caused by one of them.
And they are smarter
And make no mistake, they are smarter than us: that is what is meant by the term antibiotic resistance: they always find a way around the latest antibiotic that we invent. In other words, a given infection does not respond to antibiotic treatment, even the latest, leading to the patient’s death. This is an increasingly common problem all over the world, and is responsible for tens of thousands of deaths every year, about ten years ago an American study estimated this at over 50 000 in US hospitals, a number which must surely have increased since.
One of the reasons for development of antibiotic resistance is the abuse and misuse of antibiotics, by health personnel and lay people alike. Doctors overprescribe them, often under pressure from patients and parents of children, and also as a form of defensive medicine so as to avoid litigation from accusations of medical negligence. Another common practice is for patients not to complete the whole course of antibiotics prescribed, stopping short when they feel better. And a highly condemnable practice in Mauritius is pharmacists, who should know better, selling antibiotics over the counter to patients without prescription and, worse still, in amounts less than the proper course required. The WHO has warned that if such practices continue, we may soon reach a point when we will be left with no antibiotic to treat any infectious disease.
We are warned.
But if we behave, we need not be alarmed. Because in many cases we know enough to prevent the potentially harmful – pathogenic or disease-causing – ones from going the whole hog. Currently, for example, the Zika virus is causing a scare that started in Brazil and affects pregnant women, whose babies are born with small heads or microcephaly. It is borne by the same mosquito that carries the dengue virus, and the recommended strategy for both is primary prevention: get rid of mosquitoes by the simple hygiene and sanitary measures that everybody knows, essentially it is to get rid of places where mosquitoes breed. But we do not do that as we should for any number of reasons, and then of course, Zika or dengue strikes – through proliferation, for that’s the only thing these viruses know how to do best!
We coexist too, intimately Interestingly, one of the latest discoveries in modern medicine is the relationship of the microbes that live in our gut to our state of health. To start with, it is worth pointing out that we have microbes all over us, especially in the moist places such as our scalp, the underarms, the navel, the private parts and groins, the feet in between the toes, but also all over our skin. And they are also in our body cavities, stating with our nostrils, mouth, in the gut, urinary passage and the vagina in women. The terms ‘microbiota’ and ‘microbiome’ are used interchangeably to describe the totality of the ‘community of organisms’ that populates our body, an ‘ecological community of commensal, symbiotic and pathogenic microorganisms that literally share our body space’ – together we form an integrated ecosystem. They account for about for 1-3% of our total body mass, with some weight-estimates ranging as high as three pounds.
An account of the microbiota inhabiting human skin is almost poetic in its use of the imagery of a natural landscape: ‘Human skin represents the most extensive organ of the human body… Considered as an ecosystem, the skin supports a range of microbial communities that live in distinct niches. Hair-covered scalp lies but a few inches from exposed neck, which in turn lies inches away from moist hairy underarms, but these niches are, at a microbial level, as distinct as a temperate forest would be compared with savanna and tropical rain forest.’
As regards the gut, interestingly it has been found that each individual has a specific microbiome, that is a unique mix of microbes, and that disturbance of the microbiome – which can occur from antibiotic misuse and abuse too – may be linked to a range of diseases, including diabetes, rheumatoid arthritis, muscular dystrophy, and perhaps some cancers, as also common obesity and some psychiatric disorders. Inappropriate use of antibiotics in early childhood has been correlated with allergies in later life – another reason to use them judiciously.
Don’t get bitten!
And the mouth is home to entire colonies of microorganisms. While most of these tiny oral bacteria do us no harm, there are other species in the mix that are disease-causing and can affect our health. They need to be controlled with a healthy diet, good oral care practices and regular visits to the dentist.
Over 700 different strains of bacteria have been detected in the human mouth, though most people are only host to 34 to 72 different varieties. Most of these bacterial species appear to be harmless when it comes to our health. Others, known as probiotics, are beneficial bacteria that aid in the digestion of foods. Other bacteria actually protect our teeth and gums. There are some bacteria, however, that we’d rather do without. Indeed, one of the severest forms infection is that caused by a human bite. If ever you pick a fight with a person, try to avoid being bitten! Even a love-fight…
Other oral bugs cause tooth decay and gum disease, and they go by names that are a … mouthful: for example, Streptococcus mutans. And practically all the microbes have got such long names that are almost impossible to pronounce by lay people. Even we doctors sometimes find it difficult to mouth the latest ones!
Small is very beautiful
But what is certain is that this latest finding in biology is but the beginning of another episode in the history of our microbiome, and as it unfolds there are going to be many more as fascinating and as mind-blowing in their potential to turn around some of our pet assumptions about their relationships with us their host, and also tweak evolutionary history and even cause us to revisit our definitions of life.
Indeed, mind-blowing too can be the pictures of the microbes when they are visualized under the microscope, many of them of such exquisite design and architecture that we are left to wonder whether these oh-so-beautiful looking little ruffians are the ones that can cause us so much misery – and even death. But that’s their place and role in the scheme of things which, for all we know, we have worked out with them as partners in the evolutionary adventure…
* Published in print edition on 15 April 2016