⚠ Health caution: this page provides scientific and historical facts, not medical advice.
It was long repeated that the human body contains ten times more bacteria than human cells.
This figure circulated for decades in textbooks, articles and documentaries.
It has been revised. The current scientific estimate is much closer to one to one.
The profile of a figure that needs checking
This number had everything going for it:
- It is round: ten times. Not nine point three, not eleven.
- It is striking: it gives a powerful image — human beings would be more microbial than human.
- It is pleasant to repeat: dropped into a conversation, it makes its mark and nobody asks for the source.
These are precisely the three warning signs that help to identify a received idea.
Where did this figure come from?
The initial estimate of ten to one dates back to 1972 (by the microbiologist Thomas Luckey). It rested on a quick calculation multiplying the density of bacteria in one gram of intestinal content by the total volume of the digestive tract. This figure was then repeated as it stood, to the point of passing for an established fact: the articles that cite it all go back to this single quick calculation.1
How it was corrected
In 2016, a team redid the calculation. It started from a damning observation: the values published in the literature differed by orders of magnitude, and were only very seldom supported by measurements or calculations.2
Its results are as follows:
- The body of a seventy-kilo adult contains about 30,000 billion human cells. And, surprisingly: about 90% of them belong to the blood lineage. The human body is therefore made mostly of blood cells.
- It hosts about 38,000 billion bacteria, concentrated in the colon.3
The real ratio is therefore about 1.3 bacteria for each human cell — that is, in order of magnitude, one to one.4
It is the same mechanism as for the alleged “20% of the Earth’s oxygen produced by the Amazon” or the “80% of biodiversity”: a round number, repeated for a long time out of inertia, revised by a rigorous calculation.
The authors add a detail that is hard to forget. The two numbers are so close, they write, that a single visit to the toilet can tip the ratio in favour of human cells.5
A ratio that changes after a trip to the toilet did not deserve to be taught as a round fact.
Numerous, but light
One last figure puts things in perspective.
These thirty-eight thousand billion bacteria weigh, all together, about two hundred grams — roughly three thousandths of the body’s weight.6
However numerous they may be, these bacterial cells do not make the human being a microbial being: they are countless and minute. Counting objects and weighing matter do not answer the same question.
What most of them do
An even more important correction changes the way these organisms are regarded.
The vast majority of microorganisms do not make us ill.
They decompose dead matter, transform soils, take part in digestion and make vital substances. Disease is the exception, not the rule.
The illusion of the word “microbe”
In everyday language, the word “microbe” is often used as a synonym for dirt or danger. This popular term (coined in the nineteenth century) artificially lumps together very different beings through a pejorative lens.
The word has taken on the meaning of the exception, erasing the rule.
The real proportion of dangerous bacteria
The answer depends entirely on the question asked:
- If one counts described species: out of about 22,000 species of bacteria identified and named, a little over 1,500 are pathogenic to humans, or about 7%.
- If one estimates all existing species: taking into account the trillion microbial species that the Earth may harbour according to a 2016 estimate, the proportion of pathogens falls to about one in a billion.7
A historical selection bias
The researcher Philip Hugenholtz, responsible for updating bacterial taxonomy, highlights the cause of this gap: microbiology concentrated on a handful of bacteria that were easy to grow. Between 1991 and 1997, about 65% of published microbiological research dealt with only eight genera, among them Salmonella, Staphylococcus and Mycobacterium.8
A handful of organisms can hardly represent the roughly 5,000 species of prokaryotes then described. What we know reflects our methods of searching.
What has been measured depends directly on what was being looked for.
The question of antibiotics and resistance
During a bacterial infection, antibiotics are used to eliminate the pathogenic species. But their massive use has selected strains capable of resisting them.
- The mechanism: the antibiotic eliminates susceptible bacteria, leaving the field clear for the rare mutated individuals capable of surviving. These multiply and pass on their resistance genes.
- The impact: according to the Global Burden of Bacterial Antimicrobial Resistance study, antibiotic resistance was directly responsible for 1.27 million deaths worldwide in 2019 (and associated with 4.95 million deaths).
- A decline to be read with caution: for 2021, the same team counts 1.14 million direct deaths. But in 2020 and 2021, during the Covid-19 pandemic, other infectious diseases also fell markedly.9
That is why a figure going down is not enough: one still needs to know why it is going down. Here, the decline coincides with years in which other infections were also receding.
What a virus is, and why the definition blew apart
For nearly a century, a virus was defined by a physical property: it passes through a filter that stops bacteria. “Filterable agent” was its operational definition.
In 2003, this definition was shattered.
The discovery of Mimivirus, whose particle measures about 0.4 micrometres, revealed a virus as large as some bacteria. Detected in 1992 in the water of a cooling tower in Bradford, England, it had first been taken for a bacterium — hence its name, a contraction of “mimicking microbe”.10
A century of biology had missed an entire family of beings (giant viruses) because the sorting tool — the filter — served as the definition.
Are viruses alive?
The honest answer: it depends on the definition of life one chooses, and there is none on which everyone agrees.11
A virus does not consume energy, has no metabolism of its own and can reproduce only by hijacking the machinery of a host cell. Outside the cell, it is an inert macromolecular complex. Inside the cell, it orchestrates complex biological activity.
The question “is it alive?” is not a matter of biological fact, but a question of classification.
Three very different categories
The title groups together three sets that have no direct kinship:
| Category | Cellular organisation | Cell nucleus | Way of life / Reproduction |
|---|---|---|---|
| Bacteria | Unicellular | No (prokaryote) | Autonomous (cell division) |
| Protists | Unicellular (mostly) | Yes (eukaryote) | Autonomous (varied nutrition) |
| Viruses | Acellular | None | Obligate intracellular parasite |
Grouping them under the term “microorganisms” rests on a criterion of size, not of phylogeny.
What this site has already established
- Fermentation (Entry 9.11): the discovery of fermentation yeasts and bacteria, against the theory of spontaneous generation.
- Epidemics (Entries 3.8 and 3.11): the measurement of mortality during the infectious shock in the Americas after 1492.
Note 1
The primary source for the often cited value of ~10¹⁴ bacteria in the body dates back to the 1970s [3] and only consists of a sentence-long “derivation,” which assumes the volume of the alimentary tract to be 1 liter, and multiplies this volume by the number density of bacteria, known to be about 10¹¹ bacteria per gram of wet content.
Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016
By updating the cell counts in the body, we also revisit the 10:1 value that has been so thoroughly repeated as to achieve the status of an established common knowledge fact [4]. […] As we showed recently [4], all papers regarding the number of bacteria in the human gastrointestinal tract that gave reference to the value stated could be traced to a single back-of-the-envelope estimate [3].
Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016
Note 2
Reported values in the literature on the number of cells in the body differ by orders of magnitude and are very seldom supported by any measurements or calculations.
Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016
Reported values in the literature on the number of cells in the body differ by orders of magnitude and are very seldom supported by any measurements or calculations. Here, we integrate the most up-to-date information on the number of human and bacterial cells in the body.
Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016, open access
Note 3
For human cells, we identify the dominant role of the hematopoietic lineage to the total count (≈90%) and revise past estimates to 3.0·10¹³ human cells.
Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016
We estimate the total number of bacteria in the 70 kg "reference man" to be 3.8·10¹³. […] The vast majority of the bacteria reside in the colon
Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016
Note 4
Our analysis also updates the widely-cited 10:1 ratio, showing that the number of bacteria in the body is actually of the same order as the number of human cells
Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016
Note 5
The B/H ratio is actually close enough to one, so that each defecation event, which excretes about 1/3 of the colonic bacterial content, may flip the ratio to favor human cells over bacteria.
Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised estimates for the number of human and bacteria cells in the body”, preprint bioRxiv, 2016
Note 6
We estimate the total number of bacteria in the 70 kg "reference man" to be 3.8·10¹³. […] their total mass is about 0.2 kg […] which is about 0.3% of the body weight.
Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016
Note 7
Category species: 22857 […] The statistics refer to the public database after the last refresh (2026-10-16).
Parte, Aidan C. et al., “List of Prokaryotic Names with Standing in Nomenclature
Combining a pragmatic definition of pathogenicity with an extensive search strategy, we report 1513 bacterial pathogens known to infect humans described pre-2021.
Bartlett, Abigail, Padfield, Daniel, Lear, L., Bendall, Richard and Vos, Michiel, “A Comprehensive List of Bacterial Pathogens Infecting Humans”, Microbiology, vol. 168, no. 12, 001269, 2022
In combining this scaling law with the lognormal model of biodiversity, we predict that Earth is home to upward of 1 trillion (10¹²) microbial species.
Locey, Kenneth J. and Lennon, Jay T., “Scaling Laws Predict Global Microbial Diversity”, Proceedings of the National Academy of Sciences, vol. 113, 2016, p. 5970-5975
Note 8
Given that the study of a microorganism is simpler if you have it in pure culture on an agar plate, it is not surprising that most of what we know about microbiology comes from the study of microbial weeds. For example, approximately 65% of published microbiological research from 1991 to 1997 was dedicated to only eight bacterial genera, Escherichia (18%), Helicobacter (8%), Pseudomonas (7%), Bacillus (7%), Streptococcus (6%), Mycobacterium (6%), Staphylococcus (6%) and Salmonella (5%) [2], all of which are relatively simple to grow on agar plates. Intuitively, it seems unlikely that this handful of organisms can be representative of the approximately 5,000 validly described prokaryotic species [3], but exactly how unrepresentative are they?
Hugenholtz, Philip, “Exploring Prokaryotic Diversity in the Genomic Era”, Genome Biology, vol. 3, no. 2, reviews0003, 2002
Note 9
On the basis of our predictive statistical models, there were an estimated 4·95 million (3·62–6·57) deaths associated with bacterial AMR in 2019, including 1·27 million (95% UI 0·911–1·71) deaths attributable to bacterial AMR.
Murray, Christopher J. L. et al., “Global Burden of Bacterial Antimicrobial Resistance in 2019: A Systematic Analysis”, The Lancet, vol. 399, 2022, p. 629-655
In 2021, we estimated 4·71 million (95% UI 4·23-5·19) deaths were associated with bacterial AMR, including 1·14 million (1·00-1·28) deaths attributable to bacterial AMR. […] There was a notable decrease in non-COVID-related infectious disease in 2020 and 2021.
Naghavi, Mohsen et al., “Global Burden of Bacterial Antimicrobial Resistance 1990-2021: A Systematic Analysis with Forecasts to 2050”, The Lancet, vol. 404, no. 10459, 2024, p. 1199-1226
Note 10
During a study following a pneumonia outbreak in 1992, a microorganism growing in amoebae and resembling a small Gram-positive coccus […] was isolated from the water of a cooling tower in Bradford, England. […] We recently reported the discovery and preliminary characterization of Mimivirus, the largest known virus, with a 400-nanometer particle size comparable to mycoplasma.
La Scola, Bernard et al., “A Giant Virus in Amoebae”, Science, vol. 299, 2003, p. 2033
Note 11
Since then, reductionists and holists have opposed themselves in giving priority either to the genetic material, or the metabolic network to define life. […] The answers to this question have varied in time, depending of our knowledge about viruses and our definition of life.
Forterre, Patrick, “Defining Life: The Virus Viewpoint”, Origins of Life and Evolution of Biospheres, vol. 40, 2010, p. 151-160
Notes and sources
- ↑
Passage The initial estimate of ten to one dates back to 1972 […] a quick calculation multiplying the density of bacteria in one gram of intestinal content by the total volume of the digestive tract
The primary source for the often cited value of ~10¹⁴ bacteria in the body dates back to the 1970s [3] and only consists of a sentence-long “derivation,” which assumes the volume of the alimentary tract to be 1 liter, and multiplies this volume by the number density of bacteria, known to be about 10¹¹ bacteria per gram of wet content.
Source Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016, Results, “Revisiting the Original Back-of-the-Envelope Estimate for the Number of Bacteria in the Colon”, 1st paragraph (ref. [3] = Luckey 1972).
Open access open the source · checked on 9 September 2026
Passage This figure was then repeated as it stood, to the point of passing for an established fact: the articles that cite it all go back to this single quick calculation.
By updating the cell counts in the body, we also revisit the 10:1 value that has been so thoroughly repeated as to achieve the status of an established common knowledge fact [4]. […] As we showed recently [4], all papers regarding the number of bacteria in the human gastrointestinal tract that gave reference to the value stated could be traced to a single back-of-the-envelope estimate [3].
Source Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016, Introduction; Results, “Origin of Prevalent Claims in the Literature on the Number of Bacterial Cells in Humans”.
Open access open the source · checked on 9 September 2026
- ↑
Passage the values published in the literature differed by orders of magnitude, and were only very seldom supported by measurements or calculations
Reported values in the literature on the number of cells in the body differ by orders of magnitude and are very seldom supported by any measurements or calculations.
Source Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016, abstract.
Open access open the source · checked on 9 September 2026
Passage In 2016, a team redid the calculation
Reported values in the literature on the number of cells in the body differ by orders of magnitude and are very seldom supported by any measurements or calculations. Here, we integrate the most up-to-date information on the number of human and bacterial cells in the body.
Source Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016, open access, abstract.
Open access open the source · checked on 24 October 2026
- ↑
Passage about 30,000 billion human cells […] about 90% of them belong to the blood lineage
For human cells, we identify the dominant role of the hematopoietic lineage to the total count (≈90%) and revise past estimates to 3.0·10¹³ human cells.
Source Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016, abstract.
Open access open the source · checked on 9 September 2026
Passage about 38,000 billion bacteria, concentrated in the colon
We estimate the total number of bacteria in the 70 kg "reference man" to be 3.8·10¹³. […] The vast majority of the bacteria reside in the colon
Source Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016, abstract; Results, “Origin of Prevalent Claims in the Literature on the Number of Bacterial Cells in Humans”.
Open access open the source · checked on 9 September 2026
- ↑
Passage The real ratio is therefore about 1.3 bacteria for each human cell — that is, in order of magnitude, one to one.
Our analysis also updates the widely-cited 10:1 ratio, showing that the number of bacteria in the body is actually of the same order as the number of human cells
Source Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016, abstract.
Open access open the source · checked on 9 September 2026
- ↑
Passage a single visit to the toilet can tip the ratio in favour of human cells
The B/H ratio is actually close enough to one, so that each defecation event, which excretes about 1/3 of the colonic bacterial content, may flip the ratio to favor human cells over bacteria.
Source Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised estimates for the number of human and bacteria cells in the body”, preprint bioRxiv, 2016, Discussion.
Open access open the source · checked on 9 September 2026
- ↑
Passage These thirty-eight thousand billion bacteria weigh, all together, about two hundred grams — roughly three thousandths of the body’s weight.
We estimate the total number of bacteria in the 70 kg "reference man" to be 3.8·10¹³. […] their total mass is about 0.2 kg […] which is about 0.3% of the body weight.
Source Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016, abstract and caption of figure 3.
Open access open the source · checked on 9 September 2026
- ↑
Passage out of about 22,000 species of bacteria identified and named
Category species: 22857 […] The statistics refer to the public database after the last refresh (2026-10-16).
Source Parte, Aidan C. et al., “List of Prokaryotic Names with Standing in Nomenclature, “Numbers” page of the LPSN database (https://lpsn.dsmz.de/text/numbers): species with a validly published name under the ICNP, correct names without synonyms.
Open access open the source · checked on 24 October 2026
Passage a little over 1,500 are pathogenic to humans
Combining a pragmatic definition of pathogenicity with an extensive search strategy, we report 1513 bacterial pathogens known to infect humans described pre-2021.
Source Bartlett, Abigail, Padfield, Daniel, Lear, L., Bendall, Richard and Vos, Michiel, “A Comprehensive List of Bacterial Pathogens Infecting Humans”, Microbiology, vol. 168, no. 12, 001269, 2022, abstract.
Open access open the source · checked on 25 October 2026
Passage taking into account the trillion microbial species that the Earth may harbour according to a 2016 estimate […] the proportion of pathogens falls to about one in a billion
In combining this scaling law with the lognormal model of biodiversity, we predict that Earth is home to upward of 1 trillion (10¹²) microbial species.
Source Locey, Kenneth J. and Lennon, Jay T., “Scaling Laws Predict Global Microbial Diversity”, Proceedings of the National Academy of Sciences, vol. 113, 2016, p. 5970-5975, abstract.
Open access open the source · checked on 24 October 2026
- ↑
Passage microbiology concentrated on a handful of bacteria that were easy to grow. Between 1991 and 1997, about 65% of published microbiological research dealt with only eight genera, among them Salmonella, Staphylococcus and Mycobacterium. […] A handful of organisms can hardly represent the roughly 5,000 species of prokaryotes then described.
Given that the study of a microorganism is simpler if you have it in pure culture on an agar plate, it is not surprising that most of what we know about microbiology comes from the study of microbial weeds. For example, approximately 65% of published microbiological research from 1991 to 1997 was dedicated to only eight bacterial genera, Escherichia (18%), Helicobacter (8%), Pseudomonas (7%), Bacillus (7%), Streptococcus (6%), Mycobacterium (6%), Staphylococcus (6%) and Salmonella (5%) [2], all of which are relatively simple to grow on agar plates. Intuitively, it seems unlikely that this handful of organisms can be representative of the approximately 5,000 validly described prokaryotic species [3], but exactly how unrepresentative are they?
Source Hugenholtz, Philip, “Exploring Prokaryotic Diversity in the Genomic Era”, Genome Biology, vol. 3, no. 2, reviews0003, 2002, introduction (before the first heading), 3rd paragraph.
Open access open the source · checked on 27 October 2026
- ↑
Passage antibiotic resistance was directly responsible for 1.27 million deaths worldwide in 2019 (and associated with 4.95 million deaths)
On the basis of our predictive statistical models, there were an estimated 4·95 million (3·62–6·57) deaths associated with bacterial AMR in 2019, including 1·27 million (95% UI 0·911–1·71) deaths attributable to bacterial AMR.
Source Murray, Christopher J. L. et al., “Global Burden of Bacterial Antimicrobial Resistance in 2019: A Systematic Analysis”, The Lancet, vol. 399, 2022, p. 629-655, abstract (Summary), “Findings” section.
Open access · checked on 24 October 2026
Passage for 2021, the same team counts 1.14 million direct deaths. But in 2020 and 2021, during the Covid-19 pandemic, other infectious diseases also fell markedly
In 2021, we estimated 4·71 million (95% UI 4·23-5·19) deaths were associated with bacterial AMR, including 1·14 million (1·00-1·28) deaths attributable to bacterial AMR. […] There was a notable decrease in non-COVID-related infectious disease in 2020 and 2021.
Source Naghavi, Mohsen et al., “Global Burden of Bacterial Antimicrobial Resistance 1990-2021: A Systematic Analysis with Forecasts to 2050”, The Lancet, vol. 404, no. 10459, 2024, p. 1199-1226, abstract (Summary), “Findings”.
Open access · checked on 24 October 2026
- ↑
Passage The discovery of Mimivirus, whose particle measures about 0.4 micrometres, revealed a virus as large as some bacteria […] Detected in 1992 in the water of a cooling tower
During a study following a pneumonia outbreak in 1992, a microorganism growing in amoebae and resembling a small Gram-positive coccus […] was isolated from the water of a cooling tower in Bradford, England. […] We recently reported the discovery and preliminary characterization of Mimivirus, the largest known virus, with a 400-nanometer particle size comparable to mycoplasma.
Source La Scola, Bernard et al., “A Giant Virus in Amoebae”, Science, vol. 299, 2003, p. 2033, La Scola 2003, p. 2033, first paragraph; Raoult 2004, abstract.
Paywalled · checked on 9 September 2026
- ↑
Passage it depends on the definition of life one chooses, and there is none on which everyone agrees
Since then, reductionists and holists have opposed themselves in giving priority either to the genetic material, or the metabolic network to define life. […] The answers to this question have varied in time, depending of our knowledge about viruses and our definition of life.
Source Forterre, Patrick, “Defining Life: The Virus Viewpoint”, Origins of Life and Evolution of Biospheres, vol. 40, 2010, p. 151-160, Forterre 2010, introduction, p. 151.
Open access open the source · checked on 9 September 2026
Bibliography
13
- Bartlett, Abigail, Padfield, Daniel, Lear, L., Bendall, Richard and Vos, Michiel, “A Comprehensive List of Bacterial Pathogens Infecting Humans”, Microbiology, vol. 168, no. 12, 001269, 2022, open access (1,513 species of bacteria pathogenic to humans described before 2021). https://doi.org/10.1099/mic.0.001269
- Forterre, Patrick, “Defining Life: The Virus Viewpoint”, Origins of Life and Evolution of Biospheres, vol. 40, 2010, p. 151-160, open access; et Moreira, David et López-García, Purificación, “Ten Reasons to Exclude Viruses from the Tree of Life”, Nature Reviews Microbiology, vol. 7, 2009, p. 306-311, paywalled (the two sides of the debate on the status of life). https://doi.org/10.1007/s11084-010-9194-1
- Hugenholtz, Philip, “Exploring Prokaryotic Diversity in the Genomic Era”, Genome Biology, vol. 3, no. 2, reviews0003, 2002, open access (most microbiological knowledge comes from bacteria that are easy to grow; from 1991 to 1997, about 65% of publications dealt with eight genera; a handful of organisms hardly representative of the roughly 5,000 described species). https://doi.org/10.1186/gb-2002-3-2-reviews0003
- La Scola, Bernard et al., “A Giant Virus in Amoebae”, Science, vol. 299, 2003, p. 2033, paywalled (the giant virus, its origin and its size); et Raoult, Didier et al., “The 1.2-Megabase Genome Sequence of Mimivirus”, Science, vol. 306, 2004, p. 1344-1350, paywalled.
- Locey, Kenneth J. and Lennon, Jay T., “Scaling Laws Predict Global Microbial Diversity”, Proceedings of the National Academy of Sciences, vol. 113, 2016, p. 5970-5975, open access (the estimate of the total number of microbial species).
- Luckey, Thomas D., “Introduction to Intestinal Microecology”, The American Journal of Clinical Nutrition, vol. 25, no. 12, 1972, p. 1292-1294, paywalled. https://doi.org/10.1093/ajcn/25.12.1292
- Murray, Christopher J. L. et al., “Global Burden of Bacterial Antimicrobial Resistance in 2019: A Systematic Analysis”, The Lancet, vol. 399, 2022, p. 629-655, open access (attributable and associated deaths).
- Naghavi, Mohsen et al., “Global Burden of Bacterial Antimicrobial Resistance 1990-2021: A Systematic Analysis with Forecasts to 2050”, The Lancet, vol. 404, no. 10459, 2024, p. 1199-1226, open access (the 2021 figures and the explanation of the temporary decline by the pandemic).
- Parks, Donovan H. et al., “A Standardized Bacterial Taxonomy Based on Genome Phylogeny Substantially Revises the Tree of Life”, Nature Biotechnology, vol. 36, 2018, p. 996-1004, paywalled (the catalogue’s bias towards what we were looking for).
- Parte, Aidan C. et al., “List of Prokaryotic Names with Standing in Nomenclature (LPSN) Moves to the DSMZ”, International Journal of Systematic and Evolutionary Microbiology, vol. 70, no. 11, 2020, p. 5607-5612, open access (the number of validly named bacterial species). https://doi.org/10.1099/ijsem.0.004332; database: https://lpsn.dsmz.de/
- Rosner, Judah L., “Ten Times More Microbial Cells than Body Cells in Humans?”, Microbe Magazine, vol. 9, 2014, p. 47, open access.
- Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised Estimates for the Number of Human and Bacteria Cells in the Body”, PLOS Biology, vol. 14, no. 8, e1002533, 2016, open access (literature values that differ by orders of magnitude and are seldom supported; the ten to one, drawn from a single rough calculation and repeated until it passed for an established fact; about 30,000 billion human cells, about 90% of them of the blood lineage; 38,000 billion bacteria; a ratio of the same order; a total bacterial mass of about 0.2 kg). https://doi.org/10.1371/journal.pbio.1002533
- Sender, Ron, Fuchs, Shai and Milo, Ron, “Revised estimates for the number of human and bacteria cells in the body”, preprint bioRxiv, 2016, open access (the ratio so close to one that a single defecation can tip it in favour of human cells). https://doi.org/10.1101/036103
⚠ Data revised in line with the available scientific literature.
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