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How Bacteria Cause Diseases/Infection/Poisoning

Bacteria are those microscopic organisms that are not visible to our naked eye. There are hundred thousand of different disease caused by bacterial infection. Different bacteria have a different way to cause disease and infection. 

Bacterial have different virulent factors like toxins, superantigen, LPS, cell wall, capsule. Which are pathological to human and other animals responsible for producing the organ-specific or host-specific bacterial disease and infection.



How Bacteria Cause Diseases?

As human evolved as a species, so had bacteria in time. Over the time, bacteria have gained or lost genetic traits(Genetic Material) that enabled them to survive and adapt in this competitive time of modern science.

Gaining or losing a trait had allowed them to invade a particular environment better, survive longer in a particular niche, more effectively break down food, or, perhaps most importantly, evade detection by the immune system.

Unfortunately, some of these adaptations can wreak havoc on human bodies. In many cases, bacteria might gain or develop enhanced virulence factors, which allow them to more effectively cause disease.

Virulent bacteria, by definition, grow and thrive at the expense of their host. For instance, some bacteria might release toxins that can travel through the blood, causing life-threatening disease. Others might be able to directly degrade human tissues or trigger aggressive cascades within the human immune system.

 In fact, in many cases, the symptoms that we experience are caused by an excessive inflammatory or immune system response triggered by the infection, and not necessarily the bacteria itself.

The degree of disease that bacteria can cause depends on a few things. For instance, how important is the tissue or organ that’s affected? You can imagine that an infection of the central nervous system would be extremely serious or state of Septic Shock that can be life-threatening, while an infection of human left pinky toe might not be as life-threatening as Shock or CNS infection are.

Another factor is the particular strain of bacteria, and how much there is of it, which is called the “inoculum size”. Some bacteria, like Shigella, which causes food poisoning, require a relatively tiny inoculum size, like around two hundred, to cause serious gastrointestinal distress, while others, like Salmonella, might require several orders of magnitude more inoculum, like a million or more, to cause a serious infection.

However, the particular host factors into this equation as well. If you are immunocompromised, for instance, it might take much less Salmonella to make you sick.

Bacterial Pathogenesis

Entry Portal

Human bodies have natural defence mechanisms, such as skin, earwax, stomach acid, tears, and mucous membranes.

  • Human skin prevents microorganisms from invading,
  • human tears contain enzymes that attack bacteria,
  • human airways filter out harmful particles, and
  • human mucous membranes are coated with secretions that fight off microorganisms.

Despite the human body’s best efforts, some of these microbes are able to bypass these defences. For instance, bacteria such as

  • Salmonella,
  • Vibrio,
  • Bacillus cereus,
  • Shigella

can enter the body through ingestion. This could be from a picnic lunch left outing the sun for too long, or as the result of poor hand washing. Other bacteria, such as

  • Streptococcus,
  • Mycobacterium, or
  • Legionella

enter through inhalation, perhaps after a sick person’s sneeze, or infected aerosol particles floating through the air. Clostridium tetani, the causative agent of tetanus, enters through trauma or a wound.

Other portals of entry include a mosquito bite, needlestick injuries, or sexual transmission.

Bacteria have a vast arsenal of mechanisms to both adhere to surfaces within the body and colonize, which means to establish a microbial presence and multiply, once they’ve made contact. For instance, prokaryotic cells have short, hair-like structures called fimbriae or pili that they use to attach to various surfaces in nature.

Some bacteria have adhesins on the tips of these pili that have specifically evolved to allow them to bind tightly to cells in the human body. For example, the pili of Neisseria gonorrhoeae bind specifically to oligosaccharide receptors on epithelial cells.

Other bacteria express adhesion proteins in a variety of ways. Another bacterial adaptation that promotes colonization is the formation of biofilms, which are collectives of one or more types of microorganisms. Within a biofilm, bacteria from sticky webs of polysaccharides that bind bacterial cells together into a community, providing protection from antibiotics or host defences.

Bacteria like Pseudomonas aeruginosa can sense when enough bacteria are present and trigger biofilm formation through a process called quorum sensing. Biofilms are particularly common on catheters, in dental plaque, or on implanted surgical devices such as pacemakers.

How Bacteria Cause Damage To The Human Body?{Poisoning }

In some bacteria, natural byproducts of their growth is responsible for host tissue destruction. For instance, in the human gut environment, anaerobic bacteria, those that can survive in oxygen deficit environment, can produce toxins, enzymes, gas, and acid, all of which destroy the surrounding tissue. Some examples are Staphylococci or Streptococci.

Once the process has begun, the bacteria have momentum, with these enzymes facilitating the spread of disease. Next, Toxins are biochemical substance produced by bacteria, which are meant for their offence and defence. They help them to survive by attacking other bacteria in their species or to make a suitable environment for them by destroying the host’s immune system or cells. Typically, toxins cause degradation or lysis of cells or trigger destructive immune responses.

For some diseases, symptoms can be fully attributed to toxin production, with damage occurring right where the infection is. In other cases, such as with tetanus or certain staphylococci-associated infections, the toxin may travel through the bloodstream and cause symptoms somewhere else in the body.

The components that make up the bacterial cell wall, in particular, can set off a powerful chain reaction within the immune system. For instance, during an infection of gram-positive bacteria, the peptidoglycan and the products it breaks down into can stimulate a fever or inflammation with devastating effects on the body.

Or, lipopolysaccharide produced by gram-negative bacteria is categorized as endotoxin. In low doses, endotoxin can activate the immune system or protective responses such as a fever. In higher doses, endotoxin can trigger an extremely high fever, shock, or skin lesions, which can be deadly. Exotoxin proteins, on the other hand, can be produced by either gram-positive or gram-negative bacteria.

 Proteins that fall into this category include those that cause cytolysis, which causes a cell to burst from osmotic pressure, or receptor-binding proteins that either cause cell death, or change their function altogether. Exotoxins are often encoded on a plasmid or phage.

Another category of virulent factor is Superantigens, which activate the immune system to a life-threatening degree, causing toxic shock syndrome. Finally, bacteria have developed multiple mechanisms to escape human host defences, especially in the case of long-term infections. 

They might alter their surface proteins to evade detection, like Neisseria gonorrhoeae, physically hide within cells in the body, or inactivate human standard antibacterial defences.

One of the most powerful virulence factors that some bacteria have are slime layers called capsules. These capsules can mimic the surface of a host cell, shielding the bacteria from typical immune responses. 

Other bacteria create makeshift shields within the site of infection, like Staphylococcus aureus, which forms a barrier using coagulase. We’ve covered a lot of ground here. Ultimately, bacteria have a wide array of tricks up their sleeves. Some might express one virulence mechanism, while others might express several in tandem. Altogether, these mechanisms are ultimately what trigger disease symptoms.

Summary

To bacteria, the human body is like a playground, or a lush hotel, containing a variety of environmental niches that almost seem custom-made to suit their needs. We’ve got everything they need to grow and thrive in human nooks and crannies, from moisture and warmth to food and protection. This was all about bacterial pathogenesis, how they cause bacterial disease or infection.

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