Although they’ve developed quite a notorious reputation over the years for the
cause for a variety of deadly diseases, this is only one side of their story.
Although many may not believe it, bacteria are actually our more of our friend
than foe. Very soon you’ll find out how they are fundamental for human health, several
food processes and biotechnology.
Role in Human Health
The human body routinely harbors about 1014 bacteria
– ten times more bacteria than there are cells 1. Although they’ve developed
quite the reputation for causing diseases, there are actually many beneficial
and essential bacteria that live both on our skin and inside our bodies.
In fact, there are less than 100 species of bacteria that purposely cause
infectious diseases in humans, but more than several thousand species that exist
symbiotically in/on us 2. These bacteria that live in and on humans are part
of the microflora. Let’s take a closer look at exactly how these bacteria
promote health in humans.
Beneficial Bacteria on the Skin
bacteria that live on skin are usually either commensal (relationship
where one organism benefits without affecting the other) or mutualistic
(relationship where both organisms benefit) 3 & 4. Note that although the mutualistic/commensal do not usually cause
disease, in the rare case when there is an imbalance of them, they can also
As seen in Image 1, these bacteria can live on the skin’s surface, pores and
even sweat glands 5.
The skin flora’s main role for humans is to act as a line of
defence. They usually prevent pathogenic organisms (those that can cause
disease) from colonizing the skin surface by:
Competing against pathogens for nutrients that are provided by the
Since commensal and mutualistic microflora compete with competing invaders for
the host’s limited resources, it makes it much more difficult for invading
microbes to survive and cause a disease.
Secreting or creating chemicals such as fatty acids and bacteriocins
that kill invading microbes 6 & 3.
Stimulating the skin’s immune system so that white blood
cells such as lysosomes can destroy any pathogens on the skin 6.
One example of a bacteria on our skin that protects us is Propionibacterium
acnes. This rod-shaped bacterium uses
our body’s sebum to inhibit the growth of invading pathogens 5. It does this
by converting the triglycerides found in sebum into free fatty acids; hence
lowering the pH of skin 5 & 7. This contributes to the skin’s acidic pH
of approximately 5, limiting the growth of many common bacteria that can turn pathogenic
like Staphylococcus aureus and Streptococcus pyogenes 5 & 8.
Another similar example of a
mutualistic skin bacterium Pseudomonas
fluorescens 9. By producing the antimicrobial substance pseudomonic acid,
it not only prevents bacterial infections such as impetigo, but also inhibits
the growth of fungus species such as Candida albicans – the fungus that can cause thrush 9
& 10. To give you an idea of how effective this bacterium is at controlling
and killing pathogens that attempt to invade humans, it is actually currently
used to create a commercial antibiotic known as Mupirocin 9 & 10.
Beneficial Bacteria in the Body
the body, the gut contains the largest numbers of bacteria 11. The gut flora
is constructed during the infancy years of life and play important roles in
nutrition, digestion and immune function 12. These roles include but are not
limited to 12 & 13:
Aids in the digestion of food such as proteins and dietary carbohydrates
The gut microbiota helps with the synthesis of essential compounds
such as Vitamin B12, Vitamin K and biotin
Some intestinal flora work to protect the body against certain
kinds of infection by inhibiting the growth of harmful organisms
Without the proper balance of gut flora, not only can digestive
issues such as bloating occur, but inflammatory and autoimmune conditions such
as type 1 diabetes may also arise 14.
One example of a beneficial group of microflora are the
Lactobacillus bacteria. They are a genus of rod-shaped bacteria that have the
extraordinary ability able to produce vitamin K 15. This is important because
vitamin K is essential to the formation of proteins, blood coagulation, and bone
repair/formation 16. Vitamin K deficiency can lead to issues such as bone
fractures, bruising and irritable bowel syndrome 16.
Furthermore, Lactobacillus produces an enzyme that is capable of breaking
down lactose (a sugar found in milk) into lactic acid. This not only enables humans
to digest dairy products, but the production of lactic acid also disrupts the outer membrane of bacterial cell walls 12. This
assists in inhibiting the growth of pathogenic microbes such as E. Coli, Salmonella
and Candida albicans in the vaginal and
urinary tracts; hence reducing the possibility of infections 12.
Bacterial gut flora such as Lactobacillus is so important to human
health that the relatively new probiotic industry – which focuses on
introducing beneficial microflora into your body using foods and supplements –
is projected to be worth US$64 billion by 2023 17.
Role in Food Processing
Although it is common to hear that we don’t want any bacteria in
anything we eat, it may be surprising to hear that they are actually involved
in the production of many fermented foods.
Many dairy products are just milk products that have
been fermented over time. They almost always require a “starter culture” to
convert the sugar in milk – known as lactose – into lactic acid 18.
In cheese for example, the starting culture is usually a combination of lactococci and lactobacilli
19. Changing the mixture of the starting culture will alter the cheese’s acidity,
moisture, aroma, taste and texture 20. In addition to this, adding other strains of bacteria while the
cheese ripens will also alter the final product. For example, Swiss Cheese is
created by adding Propionibacterium Shermanii 19 & 20. The bacteria will convert the acetic
acid in milk into propionic acid and carbon dioxide; giving the Swiss cheese
its distinctive sharp taste 20.
meats such as salami, pepperoni, and dried ham also require starter cultures to
make 18. Not only are lactic bacteria used as starters, but there are a wide
variety of other bacteria that can be used to ripen the surface of the meats, alter
their flavour, and prolong shelf life 18.
For example, through the production of lactic acid, Pediococcus and Lactobacillus
are two bacteria added to increase the acidity of cured meats whilst Micrococcus
is used to reduce spoilage by converting the nitrate in the meat into nitrite 21.
Role in Modern Day Biotechnology
Major scientific discoveries such as the structure of DNA have exponentially
increased our knowledge about biotechnology 22. This has led to a variety of
new applications for bacteria in modern day advancements and improved standards
of living for many.
is a disease that occurs when one cannot create insulin properly. This means that
the glucose that one consumes is not able reach used as energy by the body’s
cells 23. This leads to issues such as excessive hunger, headaches and
Now, up until the 1980s, the only treatment for diabetes was insulin
that was extracted from the pancreas of animals such as cows and pigs 25. However,
thanks to bacteria, we now have a much more sanitary and reliable method for
producing insulin. Insulin production now occurs via the following method 26
A working gene that codes for insulin creation is extracted from a
It is combined with the DNA of a bacteria (known as a plasmid) to
form recombinant DNA
This recombinant DNA is inserted into the bacteria (Usually E.
The bacteria will reproduce with itself, creating more insulin recombinant
The recombinant bacteria will then begin using the gene to produce
human insulin. The insulin is then collected.
If anyone wants
to make sure that they understand the above method, please feel free to have a
look at Image 2, or watch the following video animation on creating insulin
recombinant bacteria: https://www.youtube.com/watch?v=H7FdzpE2GIE
a technology that enables humans to remove any gene that could turn into a
CRISPR-Cas9 is a precise genome editing tool that us to cut and
paste target segments of DNA. It works
by attaching a piece of ribonucleic acid (RNA) to the target area, which acts
as a guide telling the Cas9 enzyme where to cut. The snipped sequence can then be repaired
with a favourable mutation, allowing us to tailor specific attributes.
While this mechanism to perform miraculous genetic enhancements is
available, progress in humans is limited by our relatively exiguous knowledge
of genetics; however, this is certain to change.
At this rapid rate of technological advance, it is only a matter
of time before genetic diseases become irrelevant, and genetically enhanced
food becomes commonplace.