Michael Wilson - The Human Microbiota in Health and Disease: An Ecological and Community-based Approach

The Human Microbiota in Health and Disease

An Ecological and Community-Based Approach

The Human Microbiota in Health and Disease

An Ecological and Community-Based Approach

Michael Wilson

Cover images credited to Dr. Derren Ready

CRC Press

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Library of Congress Cataloging-in-Publication Data

Names: Wilson, Michael, 1947 April 12- author.

Title: The human microbiota in health and disease : an ecological and community-based approach / by Michael Wilson.

Description: Boca Raton, FL : CRC Press, Taylor & Francis Group, 2019. | Includes bibliographical references and index.

Identifiers: LCCN 2018017482| ISBN 9780815345855 (pbk. : alk. paper) | ISBN 9781351068369 (e-book : alk. paper)

Subjects: | MESH: Microbiota--physiology | Dysbiosis--epidemiology

Classification: LCC QR46 | NLM QW 100 | DDC 612.001/579--dc23

LC record available at https://lccn.loc.gov/2018017482

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For Andrew

And his world unseen.

In memory of

What might have been

Contents

The discovery more than three hundred years ago of the presence of tiny animalcules living in our mouths and in our gut was a truly astonishing event. Initially, we can imagine that humanitys prevailing attitude would have been one of suspicion and fear of these unknown creatures who were lurking inside our bodies. Natural responses would have been What are they doing there? and How can we get rid of them? Its not hard to understand why there would have been a feeling of hostility toward these uninvited freeloaders who were being provided with food and warmth and shelter and who, apparently, were not doing anything in return. The formulation and general acceptance of the germ theory of disease, based on the research of Louis Pasteur and Robert Koch in the latter half of the 19th century, would have done nothing to calm these fearsit had now been demonstrated that these animalcules were responsible for many of the life-threatening diseases that had been devastating humanity for millennia. No less a person than the Nobel prize-winning Elie Metchnikoff, often described as being the father of natural immunity, considered the microbes residing in the gut to be responsible for fermentations and putrefaction harmful to the host. Interestingly, his observations on the lives of centenarians in Eastern Europe led him to suggest that the adverse effects of the gut microbiota could be prevented by daily consumption of soured milk prepared by a group of lactic bacteria, or of pure cultures of the Bulgarian bacillus (i.e. Lactobacillus bulgaricus ). In other words, he was the first advocate of probiotics. Animosity toward our microbial companions persisted for a long time, and during the early 20th century many believed that humans would be healthier, and would live longer, if microbes could be eliminated from our bodies.

Once a link between microbes and disease had been established, research efforts inevitably focused on determining which microbes were responsible for the various life-threatening and debilitating infections that afflicted mankind and on developing means of preventing and treating these diseases. Enormous progress in the control and treatment of infectious diseases was made due to improvements in sanitation and hygiene, the discovery of antibiotics, and the implementation of childhood vaccination programs.

Around the time that we had become convinced that the only good microbe is a dead microbe and were becoming confident of our ability to combat infectious diseases, research on germ-free (GF) animals in the late 1950s resulted in some startling revelations. Mammals (mainly mice, rats, and guinea pigs) raised under GF conditions were found to exhibit a number of surprising differences from those raised normally. The differences observed depended largely on the particular species, but, in general, GF animals were found to have a poorly developed immune system, reduced organ size, decreased blood volume, and decreased cardiac output. These findings suggested that the microbes that lived on us were not the freeloaders we had assumed them to be, but were somehow involved in the development and correct functioning of their mammalian host. In the late 1960s, it was shown that our microbial inhabitants protected us from colonization by pathogens, and we now know that, by detoxifying harmful chemicals in our diet, they can also protect us against cancer. Importantly, they also provide us with energy, vitamins, and essential amino acids. More recent research implies that our indigenous microbiota may affect us in a surprising number of additional ways. For example, there is some evidence to suggest that they can also influence our behavior. Far from being a worrying presence in our body, microbes are now recognised as being essential for our development, health, and well-being. We have now come to realize that a human being is a symbiotic association comprised of a huge number of microbial symbionts and their mammalian hostsuch an association is known as a holobiont.