THE 10 MOST COMMON PATHOGENIC BACTERIA FOR MAN - BIOLOGY - 2025

The pathogenic bacteria are those that produce diseases. In general, bacteria are microorganisms that are present in all media: air, water, and even within the human body.

Therefore, it is necessary to consider that not all bacteria are pathogenic. In fact, some bacteria present within the human body perform important tasks within the different organs. Therefore they are necessary for the healthy functioning of the body.

Bacteria illustration

Pathogenic bacteria, on the other hand, are those that, when spread, cause infectious diseases. These infections can occur due to person-to-person contact, animal bites, food intake, or contact with contaminated environments.

List of pathogenic bacteria

Staphylococcus or Staphylococci

Staphylococcus are one of the families of bacteria that cause major diseases in humans. These microorganisms live naturally on the skin and mucosa of healthy people without causing any problems.

However, when environmental conditions permit, staphylococci can cause infections of different kinds. These can be superficial like folliculitis or more serious like UTIs in sexually active women and pneumonia.

In addition, they can produce a wide variety of toxins that cause food poisoning and toxic shock syndrome.

Streptococcus or Streptococci

Streptococcus are also a family of bacteria that occurs naturally in the human body. However, some strains are responsible for causing extremely serious diseases.

Streptococci pyogenes are responsible for bacterial pharyngitis. This infection is not serious if it is given the right treatment, but otherwise it can lead to serious sequelae such as rheumatic fever.

Other infections caused by strep include impetigo and flesh-eating bacteria. This bacteria causes rapid destruction of the skin and muscle, which can be fatal.

Escherichia coli

Escherichia coli is part of the family of Gram-Negative bacilli. This bacteria is normally found in the intestinal tract naturally without causing harm. In fact, it has a positive function because it prevents the overgrowth of other pathogens.

In situations such as surgery or accidents, Escherichia coli can leave the intestine and cause very dangerous diseases in contact with other tissues. For example, it can cause severe gastrointestinal infections and kidney damage.

Salmonella

Salmonella is also part of the Gram-Negative bacilli. This bacterium is known to cause severe gastrointestinal infections and salmonellosis.

Pathogenic salmonellae are ingested in contaminated food and survive the gastric acid barrier. Therefore, they can reach the small intestine and there they produce toxins that cause an inflammatory reaction.

This reaction can cause diarrhea, ulcers and destruction of the mucosa. Also, bacteria can spread from the intestines to cause disease in other organs.

Shigella

Shigella is another bacterium part of the Gram-Negative bacilli and is known to be responsible for dysentery.

Like Salmonella, Shigella is transmitted through consumption of contaminated food or person-to-person contact and can resist transit through stomach acids. This is how it reaches the small intestine, where it reproduces.

This bacterium has been responsible for many deaths around the world. In developed countries it is spread by contact with fecal matter, a situation that occurs most frequently in daycare centers or during anal intercourse.

In the case of developing countries, the spread also occurs through contaminated food or through the consumption of unsafe water.

Spirochaetes or spirochetes

Spirochetes are part of the Gram-negative bacilli family and can live freely or within the gastrointestinal tract of some animals.

However, some strains of this bacteria are responsible for diseases such as syphilis, which is transmitted sexually, and Lyme disease, which is transmitted by the bite of the deer tick.

Spirilla

Spirilla is also a Gram-Negative bacillus and is transmitted through foods such as undercooked poultry, shellfish, and untreated drinking water. This bacterium is responsible for bacterial diarrhea in children and certain types of gastric ulcer.

The latter is caused by Helicobacter pylori, a strain that is capable of colonizing the gastric mucosa of humans, that is, the lining of the stomach.

This bacterial colonization is the cause of the ulcer and there is even evidence of its participation in the development of stomach cancer.

Neisseria

Neisseria is found naturally in the mouth and female genital tract. However, there are two species within this family of bacteria that can cause very serious illnesses.

Neisseria gonorrhoeae is the bacteria that cause sexual infection gonorrhea. This is a disease that, when not treated in time, can lead to more serious conditions such as gonococcal arthritis and pelvic inflammatory disease.

On the other hand, Neisserial meningitis is the agent that causes meningococcal meningitis. This disease that occurs in the cerebrospinal fluid and meninges leaves serious sequelae and is potentially fatal.

Vibrios

Vibrios are bacteria that are particularly found in aquatic environments, especially in marine environments. Therefore, they can be found in some fish, squid and other species in the sea.

Vibrio cholerae is responsible for cholera, an infectious disease known for the speed with which it can lead to death. Due to the colonization of this bacterium, severe diarrhea occurs and quickly leads to dehydration.

Haemophilus influenzae

Haemophilus influenzae was known as the flu bacteria until 1933 when it was discovered that it was also responsible for other diseases such as meningitis, epiglottitis, pneumonia, ostiomyelitis, and sepsis.

This family of bacteria usually lives in the human body without causing problems. However, when there is a reduction in the response of the immune system, it can spread to cause diseases such as those mentioned.

This bacterium especially affects the respiratory tract and is usually the main cause of respiratory infections in children and the elderly in developing countries.

References

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4. Microbiology in pictures. (SF). Pathogenic bacteria and infectious diseases. Recovered from: microbiologyinpictures.com
5. Todar, K. (SF). Bacterial pathogens of humans. Recovered from: textbookofbacteriology.net.