Have we done anything defective to the bacteria that they launch a revenge attack on us? Or is it completely an unprovoked intrusion? Why do bacteria infect humans?
Most of us would have encountered some type of bacterial infection or at least would have heard about such infections in our day to day life.
There are several common infections we often pick up such as urinary tract infection (a bacterial infection of the bladder, urethra, kidneys, or ureters), respiratory tract infections which include sore throat, bronchitis, sinusitis and pneumonia, gastrointestinal infections due to bacterial food poisoning, etc.
Some bacterial infections are rare that caught our attention only in the news like anthrax, a rare infectious disease caused by the bacteria Bacillus anthracis.
A few bacterial infections are life-threatening for instance tetanus. Tetanus caused by a toxin called tetanospasmin produced by the bacteria called Clostridium tetani, which leads to severe muscle spasms and sometimes death.
Cholera, another bacterial infection by Vibrio cholera requires immediate treatment because the disease can cause death within hours due to dehydration.
Why do bacteria infect humans Vs How do bacteria infect humans?
Let’s go through the above-mentioned examples of bacterial infection for a better understanding.
Why do we get a urinary tract infection?
A bacterium called Escherichia coil can cause urinary tract infections (other bacteria can also cause urinary tract infection). E.coli present in the gastrointestinal tract spread from the anus to urethra and they enter the urinary tract through the urethra and begin to multiply in the bladder.
Women are more prone to this infection because of their anatomy. However, trauma to the urethra from surgery, catheterization, and childbirth can predispose to getting UTI. A sudden increase in sexual activity can also be a trigger.
In the case of respiratory tract infections, the causative bacteria are often spread in the coughs and sneezes of the infected person.
Tetanus is caused by a toxin, tetanospasmin. When the spores (dormant structure of the bacteria which is not metabolically active, formed in response to the harsh environmental condition for the survival) of the bacteria, Clostridium tetani which are found in soil, dust and animal feces enter a deep flesh wound, they grow into bacteria that can produce a powerful toxin called tetanospasmin.
Cholera is caused by eating food or drinking water contaminated with a bacterium called Vibrio cholerae.
Nevertheless, why do we get a bacterial infection resolves the HOW!
Yes, unfortunately, we came across these bacteria, but why can’t they just say Hi and go away? Why do they have to make us sick?
Why do bacteria infect humans?
There were few reports which brought light to the fact that some animals like Tiger, Camel, Octopus, Skuas, Crow, a Siberian tiger can hold a grudge and took revenge against humans.
Are bacteria one among them?
Neither we are scientists who manipulate them with the laboratory experiments nor we are physicians who sabotage them by prescribing antibiotics.
Bacteria don’t take anything personally. It’s purely the survival strategy.
All forms of life are driven by survival skills and their propagation. So do bacteria!!!
We, humans, provide them with food and shelter and that’s why we are host to the microbes. We are home to the bacteria.
What is the human body to a bacterium?
The bacteria infect humans mainly because the human body caters to an environment where bacteria can survive and multiply.The #bacteria #infect humans mainly because the human body caters to an environment where bacteria can survive and multiply. Click To Tweet
The genetic traits of the bacteria provide the means to enter (invade) the environment (which is the human body), remain in a niche (adhere or colonize specific organs or parts of the body), gain access to food sources (by using specific degradative enzymes), and escape clearance by host immune and non-immune protective responses.
To a bacterium, the human body is a collection of environmental niches that provide them with
3. Food, necessary for growth.
The average normal human body temperature is 37° C (98.6° F) and humans are capable of self-regulating the body temperature to one degree above or below 37° C.
The bacteria with an optimum temperature (Optimum temperature is the temperature at which the bacterial growth is highest) in the range of 30° C – 39° C are called mesophiles. Mesophiles thrive happily on the human body temperature and most warm-blooded animals.
Most of the human pathogenic bacteria (disease-causing bacteria) are mesophiles.
E. coli, the bacteria found in our gut is a mesophile with an optimum temperature of 37° C. Streptococcus pneumonia found in the upper respiratory tract including throat and nasal passages is also a mesophile with an optimum growth temperature range of 30° C – 35° C.
Bacteria love to live in a moist environment. Water constitutes approximately 70 % of a bacterial cell. But unlike animals or humans, bacteria cannot ingest water rather it must rely on an environment that has enough water.
And the human body is such a nesting ground with enough moisture. Approximately 60 percent of the adult human body is water which makes an important environment for the bacteria.
However many bacteria can survive for extended periods without moisture, but without it, they cannot grow and reproduce.
To build the proteins, structures, and membranes that makeup and power the cell, bacteria require
- The raw materials (mainly Carbon, Hydrogen and Nitrogen)
- Source of energy
The human body is rich in carbohydrates, proteins, vitamins, minerals, and other chemicals that bacteria can use as nutrients.
For example, let’s see how bacteria take up carbohydrates.
Carbohydrates are molecules made exclusively from carbon, hydrogen, and oxygen. These three molecules are arranged into a ring structure for simple carbohydrates such as glucose and those rings are put together into long complex branching chains for complex carbohydrates such as starch and cellulose.
Simple carbohydrates like the glucose are easy to metabolize and can be used to power up ATP (the molecules that cells uses for energy) or in the synthesis of proteins.
More complex carbohydrates like starch or cellulose take a bit more effort, as they need to be broken down into their component simple sugars before they can be processed. To break them down, bacteria use specific enzymes.
Two other important environmental conditions for the bacteria to grow are pH and the availability of oxygen.
Different parts of the human body maintain different pH though we say the pH of the human body is 7.4 which is the human blood pH. Therefore different types of bacteria colonize different parts of the body according to their pH preferences.
The pH of the oral cavity is between 6.5 – 7.5 and it’s the godown of numerous bacteria. The environment in the mouth is apt for the growth of characteristic bacteria found there. The mouth is a rich environment not only because of the pH condition but also it is very watery and a lot of nutrients pass through the mouth each day.
These resident microbes of the mouth adhere to the teeth and gums to resist the mechanical flushing from the mouth to the stomach which is highly acidic and can kill the acid-sensitive bacteria.
The stomach is the most acidic part of the human body with a pH of 1.5 – 4 and not an advisable environment for the bacteria.
Surprisingly the courageous Helicobacter pylori, an alkali loving bacteria survive and reside in the strongly acidic environment of the stomach by making a micro alkaline environment for it in the stomach which was the Nobel prize-winning discovery in medicine in 2005.
Our intestines, which are alkaline with a pH of 7 – 8.5 is home to a variety of bacteria such as Lactobacillus, the bacteria commonly used in probiotic foods such as yogurt.
Facultative anaerobes are bacteria generally grow better in oxygen but are still able to grow well in their absence.
Many medically important microorganisms are facultative anaerobes as there is a mixture of aerobic (presence of oxygen) and anaerobic (absence of oxygen) microenvironments in the human body.
Staphylococcus and E. coli are examples of facultative anaerobes.
Some organisms such as Clostridium perfingens which cause gas gangrene cannot grow in the presence of oxygen. Such bacteria are referred to as obligate anaerobes.
Tuberculosis is initiated by the deposition of Mycobacterium tuberculosis, contained in aerosol droplets, onto lung alveolar surfaces.
Mycobacterium tuberculosis requires the presence of molecular oxygen for metabolism and growth and is therefore referred to as obligate aerobes. And lungs are such a wealthy environment with oxygen.
The bacteria which don’t enjoy this environment (human body) die off and only thrive in their other suitable environment.
However, the bacteria which appreciate this environment stay with us and survives on the human body.
Unfortunately, many of the mechanisms used by most of the bacteria to grow in their environment and the by-products of their growth cause damage to us.
The disease caused by the bacterial infection is not just the damage caused by the bacteria but also by the consequences of the immune responses our body produced to the infection. These disease-causing bacteria are called pathogens.The #disease caused by the #bacterialinfection is not just the damage caused by the #bacteria but also by the consequences of the #immuneresponses our body produced to the #infection. Click To Tweet
Several other bacteria do not cause damage or disease but still adore their human body environment. They are beneficial bacteria or normal flora such as the residents of our gut.
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What are your insights on bacterial infection, let me know in the comments below.