10 MICROORGANISMS HARMFUL TO HUMANS - BIOLOGY - 2025

Some of the most common harmful microorganisms for humans are Escherichia coli, Streptococcus pneumoniae, Salmonella or Bacillus cereus. Microorganisms are harmful to humans when they bring diseases to the body, attacking cells that are vital to the functioning of the body.

These harmful microorganisms can be divided into three large groups. The first are bacteria. They are unicellular and have no nucleus. They can live inside or outside of a cell and release toxins. In turn, bacteria are classified into cocci, bacilli and spirilli.

The second harmful microorganisms are viruses, although they are not considered living beings but rather primitive particles that contain DNA or RNA. Viruses must enter cells to reproduce and infect them by changing their genetic material.

Lastly, we have the mushrooms. These can lead to infections in the outer parts of the bodies. For example, the skin or mucous membranes, which are in constant contact with the outside.

To get rid of these microorganisms, man needs to combat them with antibiotics, antivirals or antifungals, as appropriate.

Common microorganisms harmful to humans

1- Escherichia coli

It lives inside the intestines and is one of the most studied bacteria. It helps in the digestive process and produces vitamins B and K.

But, in moments of low defenses it can affect the human organism, especially the urinary and digestive tracts.

Diseases it causes: kidney failure, hemorrhagic diarrhea.

2- Mycobacterium tuberculosis

It is one of the oldest known microorganisms. It is also known as Tisis. It can make any organ sick, the lungs and liver being the most commonly affected.

It is highly resistant to cold and affected by heat. It infects an average of 9 million people annually.

3- Streptococcus pneumoniae

It can cause sinusitis, otitis and pneumonia. These infections are becoming more lethal and accentuated in underdeveloped countries. This bacterium works as a single agent or it can act in association with a virus.

Meningitis is one of its most worrisome presentations. It is unique to humans.

4- Salmonella

It is a bacterium that can cause multiple diseases, the main ones being diarrhea. It is a genus of bacilli that is divided into two species: Salmonella bongori and Samonella enterica.

This bacterium can last several weeks in dry environments, without needing water. It is spread through feces and urine.

5- Yersinia pestis

It is a gammaproteobacteria that can cause plague. It causes an infection that lodges in the lymph nodes, the blood or the lungs.

It is housed in rodents but is transmitted by the bite of an oriental flea that lives in rats.

6- Tetanospamine

Releases an enormously powerful neurotoxin. It can be found as a spore that lives in the soil for up to 40 years with the ability to infect.

Its spores penetrate wounds and invade the body. It was known for its association with injuries and seizures.

7- Vibrio cholerae

It produces cholera, a very acute infectious and contagious disease. It consists of diarrhea and rapid dehydration.

8- Treponema pallidum

It is a bacterium of the genus schiroqueta. It causes syphilis, a sexually transmitted disease. It is quite fragile and does not survive long outside the body. Your best antidote is penicillin.

9- Bacillus cereus

It is responsible for complex food poisoning. Causes diarrhea, nausea, and vomiting. It is present in food and multiplies easily at room temperature.

10- Mycobacterium leprae

Also known as Hansen's bacillus, it is the bacteria that causes leprosy.

It mainly affects the nerves, skin, respiratory tract, and eyes. They reproduce quickly, so it is contagious.

References

1. Good bacteria and bad bacteria. (2013). Science of nature 1st that. Recovered from es.slideshare.net
2. Brock - Biology Of Microorganisms 10th Ed
3. National Institute of Hygiene and safety in Trbajao. Clostridium tetani. Databio. Recovered from insht.es
4. World Health Organization. Microbiology of M.leprae. Retrieved from who.in
5. World Health Organization. (2016). Salmonella (not typhoid). Retrieved from who.int
6. PREADO J., VALERIA. (2001). Microbiological concepts of Streptococcus pneumoniae: BASIC MICROBIOLOGICAL ASPECTS. Chilean journal of infectology, 18 (Suppl. 1), 6-9.