authorbio Trudy Wassenaar, Ph.D.,
is a molecular biologist specializing in
microbiology. She has done research at the
University of Amsterdam and the University of
Utrecht ...
biodiversity:
microorganisms Bacteria: More Than
Pathogens By Trudy M. Wassenaar,
Ph.D. An
actionbioscience.org original
article
articlehighlights There are more bacteria on
Earth than there are humans. Bacteria:
inhabit every
environment on the planet, playing a key
ecological role
can be good for our
health -- for example, by helping us digest
food
can cause disease, but
the human body is not the natural host for many
bacteria
Bacteria: More Than
Pathogens By Trudy M. Wassenaar, Ph.D.
Bacteria are usually
associated with dirt, disease, and
death.
Misunderstood bacteria
Bacteria suffer from negative public
relations. You probably associate bacteria with
the three D's: dirt, disease and death. And
indeed, for centuries bacterial infections were
the major cause of infant and child mortality
worldwide. Child mortality began to decline after
people were educated about better hygiene. The
decline continued with the introduction of
antibiotics for better treatment and vaccination
for prevention of common deadly
diseases.
Bacteria are certainly involved in dirt,
disease and death, to which we should add decay.
Spoilage of leftover food, decomposition of garden
cuttings, decay of dead bodies, or smelly water in
a forgotten vase, are all the result of bacterial
activity. As is body odor, caries, strep throat,
or bubonic plague, to name a few diseases from
both ends of the spectrum. No wonder that bacteria
receive a bad press.
Bacteria that caused
large-scale disease in our history may be close to
extinction.
Commercials want us to believe that the
only good bacterium is a dead bacterium.
Antimicrobial agents are added to tooth paste,
soaps, detergents, and plastics. There is no
Society for the Protection of Bacteria, although
there is a satirical initiative for the Ethical
Treatment of Bacteria.1 Some
bacteria may even hover on the edge of extinction,
and it is no coincidence that these are pathogenic
(disease-causing) bacteria such as Salmonella
typhi (the cause of typhoid fever) or
Yersinia pestis (the cause of plague).
Fortunately for the little critters, populations
survive in remote areas where they are not
efficiently hunted with vaccines and
antimicrobials, and people are still at risk for
the diseases they cause in these places.
The bacterial kingdom
It is about time we take a closer look at
the Bacterial Kingdom, with capitals. For a
Kingdom it is, biologically speaking, and the
ancient lineage, diversity, and evolutionary power
of its inhabitants deserve royal treatment rather
than disgust.
A bacterium differs
from a virus in its structure and in the way it
inhabits a host.
Before kindling fascination for the
world of bacteria, a common misconception must be
cleared: bacteria are not viruses.
Whereas most bacteria live as independent
cells with a membrane to separate them from the
outside world, viruses can only multiply inside,
and to the detriment of, the cells they infect.
Interestingly, some viruses, called
bacteriophages, have specialized to infect
bacteria.2,3
Viruses consist only of genetic material
(DNA or RNA) surrounded by a protein shell. They
cannot metabolize and once inside a host cell,
their genetic material hijacks the cell's
machinery to produce replicas of the
virus.
Bacteria are much more similar to you and
me. They exhibit the basic characteristics of
all living things -- they breathe, metabolize,
produce waste, and maintain a membrane
potential. However, they do not have a nucleus
in which their DNA is separated from the rest of
the cell, as plants and animals do, and that is
the major distinction between prokaryotes (a
type of cell that most microorganisms are made
of, including all bacteria) and eukaryotes (a
different type of cell making up nucleated
microorganisms, such as yeasts, or cells in an
organism, e.g., human).
Both viruses and bacteria can cause
disease. However, not all types of viruses cause
disease in humans, and not all bacteria cause
disease.
The majority of
bacteria are harmless and some are
beneficial.
Another common misconception is that all
bacteria are bad for you. Some bacteria you'd
better not meet, but the majority of them are
completely harmless, and some are highly
beneficial to us. Confusingly, certain bacteria
can be beneficial to some animals, and pathogenic
to others. More commonly, pathogenic bacteria are
harmful only to a limited number of hosts, or even
only to one, whereas they live happily within
other hosts without causing trouble. If the
suffering host happens to be human, the culprit
bacteria are called human pathogens; however, from
the bacterial point of view, humans are just the
wrong host to be in. So who is to blame for the
disease?
Harmless bacteria can
become deadly in certain
circumstances.
Most bacteria are completely
harmless
Although a tree can kill a person when it
falls, we usually don't regard trees as harmful.
The same is true for most bacteria -- although
they may cause problems under specific conditions,
they usually live their lives without interfering
with ours. An example is Pseudomonas
aeruginosa, which commonly lives in soil
without doing harm. However, if it is inhaled by a
person with Cystic Fibrosis, it can colonize their
lungs and cause lethal
infections.4
The human body is not
the natural environment for many
bacteria.
For many bacteria, the human body is
not the right place to live in at all.
They couldn't cope with the lack of
oxygen (inside our cells the oxygen
concentration is lower than that of air) or with
the presence of oxygen (for bacteria that live
in oxygen-deprived environments, oxygen is
toxic).
They couldn't withstand our defense
mechanisms such as the salt present on our skin
and in our tears, the lack of iron (a smart
device keeps iron, a vital element to all living
organisms, inaccessible to most microorganisms
in our body), or with the toxic radicals that
cells release when under attack of
bacteria.
It could be too warm for them, or too
cold, as certain bacteria have specific
temperature requirements to grow.
Or they could be deprived of food, as the
members of the Bacterial Kingdom have
specialized to live on almost anything, but each
species has specific nutrient needs.
In conclusion, we have little to fear
from most bacteria that we encounter.
Our bodies can resist
most bacterial attacks.
It is no big surprise that we are
relatively inert to bacteria. After all, mammals
have evolved in the presence of bacteria, and have
developed specialized strategies to keep bacteria
under control. In contrast to what your mother
taught you, soap is not essential to survive. Our
body can resist the bombardment of bacteria it
receives every day quite efficiently. Just as well
that we can't see them (for the idea is
unpleasant) but with every breath of air, every
bite we take, little bugs are unknowingly entering
our body. And this shouldn't worry you in the
least. As long as you keep the troublemakers --
the real pathogens -- out.
The human body is home
to millions of beneficial
bacteria.
We couldn't live without
bacteria
We house millions of bacteria on our skin
and in our nose, mouth, and gut:
up to 500 species can be found as normal
oral flora5
there can easily be 25 species living in
a single mouth
a milliliter of saliva can contain as
many as 40 million (4 x 107)
bacterial cells6
108 bacterial cells present in
the cecum (the initial part of the colon) per
milliliter of content is normal and many of
these species are different from those found in
the mouth7
Strictly speaking, the inside of our mouth,
stomach and intestines are part of our outer
surfaces. Although they are inside our body, their
surfaces are in direct contact with the outside
world, and as food particles pass the mucosal
inner lining of our intestines, hitchhiking
bacteria can stay there and multiply. We are born
sterile (free of bacteria) but within hours we are
colonized by our little friends, not to be left
alone again.
Antibiotics can wipe
out our body's beneficial bacteria, causing
unwanted health consequences.
Without bacteria we would not survive.
They help us digest our food, produce vitamins,
and occupy niches that would otherwise be
available for competing pathogens. This
competitive effect becomes apparent when we wipe
out a large proportion of our intestinal flora,
for instance by an antibiotic that is prescribed
to treat a bacterial infection. Diarrhea is
frequently the unwanted result, as 'foreign'
bacteria take their chance to occupy the 'empty'
niches. Healthy bacteria take over in time, so
that in most cases the side effects of antibiotics
are soon gone. Bacterial populations grow into a
state of equilibrium until some external factor
disturbs it again.
Certain foods and the
way we process food depend on
bacteria.
We can buy supplements
or foods with beneficial
bacteria.
Certain bacteria are good for
you
For centuries, people have eaten certain
food deliberately for the bacteria it contains and
have used bacteria in food preparation.
The best-known example is the consumption
of yogurt and other fermented milk products,
which have the combined effect of reducing
spoilage, and enhancing tolerance for partially
lactose-intolerant individuals.
A major industry has developed to produce
bacterial preparations, in the form of powders,
drinks, and dairy products; all sold as healthy
and beneficial (and sometimes tasty)
supplements. Although some of their promises are
unrealistic (some products don't even contain
viable bacteria), it is generally accepted that
certain bacteria are beneficial, especially when
intestinal flora is unbalanced (as with
antibiotic-associated diarrhea). The most
commonly used bacterial species as so-called
probiotics are lactobacilli and
bifidobacterium.8
A number of bacterial species are
required for the preparation of food, and may or
may not arrive on our plate
alive.9 Notably, many cheese
varieties are dependent on their characteristic
bacterial starter culture. Fermenting bacteria
are required to produce sausages and sauerkraut;
they even help cacao and coffee beans to attain
their desired flavor.10
Conclusion: Bacteria
are essential to human health and the world's
ecosystems.
Earth: the planet of bacteria
In a gram of soil, approximately
108 bacteria are
present11 and these are
estimated to represent over 10,000 species.
Interestingly, there are more than 1030
bacteria on earth, compared with fewer than
1010
humans.12
Bacteria were the first living organisms
found on Earth.
They inhabit deserts, ice caps, oceans
and hot springs.
The number of bacterial species worldwide
is estimated to be more than a thousand
million.11 Their individual
sizes may be insignificant, but their number and
diversity is unimaginably large.
Bacteria contribute substantially to the
total biomass in marine environments.13
And, since oceans cover 70% of our
planet's surface, bacteria make up a significant
part of the total biomass on Earth.
These facts are truly impressive for
organisms so small that they are invisible to the
eye. It is to our advantage to look at bacteria as
more than just pathogens.
About the author: Trudy Wassenaar, Ph.D., is
a molecular biologist specializing in
microbiology. She has done research at the
University of Amsterdam and the University of
Utrecht (The Netherlands), as well as at the
University of Mainz (Germany), for over 15 years.
In 2000, she founded a consulting company to
assist research groups in academia and
governmental agencies with the development of
research strategies and dissemination of results.
She is Curator of the Virtual Museum of Bacteria
(supported by the Foundation for Bacteriology). http://www.bacteriamuseum.org/homepageTW.shtml
Virtual Museum of Bacteria This
site brings together information and links on
bacteria, bacteriology, and related topics
available on the web, as well as images of
bacteria. http://www.bacteriamuseum.org/
CELLS
Alive! Unique images of microorganisms that
cause illness, and the blood cells that do battle
to keep you well. Includes links to sites offering
further information on microbiology, infectious
diseases and cell biology. http://www.cellsalive.com/
The Microbe Zoo A visually
stimulating visit to Dirtland, Water World, and
other pavilions in this virtual zoo to discover
the microbes that inhabit different environments.
Good introduction to microbes for young people and
adults who know little about the critters. http://commtechlab.msu.edu/sites/dlc-me/zoo/
Microbiology portal Microbes.info
is a good starting point for finding information
concerning microbiology. http://www.microbes.info/
The
Bad Bug Book This handbook, developed by
the U.S. Food and Drug Administration, provides
basic facts regarding foodborne pathogenic
microorganisms and natural toxins. A useful
reference for professionals in the food
industry. http://vm.cfsan.fda.gov/~mow/intro.html
Clean Hands campaign The American
Society for Microbiology asks you to spread the
"importance of handwashing." The site offers educational
materials designed for healthcare professionals and
consumers including posters, a brochure, and stickers,
which can be downloaded from the site. http://www.washup.org/
Virology meetings worldwide A compendium
of current events in virology, with information on
meetings and registration. Of interest to professionals
and students. http://www.virology.net/garryfavwebmeet.html
1) "Resolution of the National Organization
for the Ethical Treatment of Bacteria," a
satirical campaign, accessed online 7-02 but no
longer available (was
http://www.island-of-freedom.com/satire/bacteria.htm) 2)
"Bacteria can be ill." Cells Alive! http://www.cellsalive.com/ 3)
"Oh goodness, my E. coli has a virus!"
Cells Alive! http://www.cellsalive.com/phage.htm 4)
Brennan AL, Geddes DM. 2002. "Cystic fibrosis."
Curr Opin Infect Dis;
15:175-182. 5) Paster BJ, Boches SK,
Galvin JL, Ericson RE, Lau CN, Levanos VA,
Sahasrabudhe A Dewhirst FE. 2001 "Bacterial
diversity in human subgingival plaque." J
Bacteriol; 183:3770-3783. 6) Aps JK, Van
den Maagdenberg K, Delanghe JR, Martens LC. 2002.
"Flow cytometry as a new method to quantify the
cellular content of human saliva and its relation
to gingivitis." Clin Chim Acta;
321:35-41 7) Marteau P, Pochart P, Dore J,
Bera-Maillet C, Bernalier A, Corthier G. 2001.
"Comparative study of bacterial groups within the
human cecal and fecal microbiota." Appl Environ
Microbiol; 67:4939-4942. 8) Saarela M,
Mogensen G, Fonden R, Matto J, Mattila-Sandholm T.
2000. "Probiotic bacteria: safety, functional and
technological properties." J Biotechnol;
84:197-215. 9) "Good bacteria in food."
The Virtual Museum of Bacteria. http://www.bacteriamuseum.org/niches/foodsafety/goodfood.shtml 10)
"What role, if any do yeasts play in the cocoa
production process?" International Cocoa
Organization. http://www.icco.org/questions/yeast.htm 11)
Bach HJ, Tomanova J, Schloter M, Munch JC. 2002.
"Enumeration of total bacteria and bacteria with
genes for proteolytic activity in pure cultures
and in environmental samples by quantitative PCR
mediated amplification." J Microbiol
Methods; 49:235-245. 12) William B.
Whitman, David C. Coleman, and William J. Wiebe.
1998. "Prokaryotes: the unseen majority."
PNAS 95: 6578-6583.
Actionbioscience.org Editor's Note (11/02): The
biomass of the world's humans plus their domestic
livestock is only exceeded by the estimated
combined biomass of the world's bacteria,
according to the World Atlas of Biodiversity:
Earth's Living Resources for the 21st Century,
United Nations Environment Programme World
Conservation Monitoring Centre (University of
California Press, 2002). 13) Fukuda R,
Ogawa H, Nagata T, Koike I I. 1998. "Direct
determination of carbon and nitrogen contents of
natural bacterial assemblages in marine
environments." Appl Environ Microbiol;
64:3352-3358.
Actionbioscience.org original
lesson This lesson has been written by a
science educator to specifically accompany the
above article. It includes article content and
extension questions, as well as activity handouts
for different grade levels.
Lesson
Title:Bacteria: Friend or
Foe? Levels:
middle school - undergraduate Summary:
This lesson explores "good" and "bad" bacteria.
Students can draw "Wanted!" bacteria mug shots,
create composting trials and designs, produce a
skit involving a boastful virus and bacterium,
experiment with soil and ordinary objects in the
lab, write a news story about an outbreak,
complete a multiple-choice bacteria quiz … and
more! http://www.actionbioscience.org/lessonaccess/wassenaar.html
