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What is Pathogenic Bacteria?

Mary McMahon
Updated Mar 03, 2024
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Pathogenic bacteria are bacteria which are capable of causing disease. Humans are generally most interested in the species of bacteria which can cause disease in humans, although these bacteria can also infect other animals and plants. Some notable pathogenic bacteria include Streptococcus, Staphylococcus, Tuberculosis, and Escherichia coli, among many others. Worldwide, these bacteria account for many illnesses and disease epidemics.

Intracellular bacteria are pathogenic bacteria which always cause disease when they enter the human body, in contrast with conditional bacteria, which can cause infections and disease in certain circumstances. Many bacterial are conditional, taking advantage of happenstance like an open wound to duplicate themselves and spread disease. Opportunistic bacteria are bacteria which do not normally cause disease, but will if a patient has a compromised immune system.

Many humans actually host large numbers of bacteria at any given time. These bacteria are known as commensal or “good” bacteria, because they perform some vital and useful functions in the human body. Commensal bacteria in the gut, for example, help to break down and digest food.

Pathogenic bacteria can be spread through a human population in a range of ways. Air, water, and soil are all common vectors, and people may also pass bacteria directly to each other through physical contact. Some bacteria are very adept at colonizing locations like door knobs and medical equipment, allowing them to move from person to person with ease, while others are much less virulent, and will die off if they are away from a human host for too long.

Tuberculosis is one of the world's leading killers, making it a pathogenic bacterium of particular interest. Pathogenic bacteria are also responsible for intestinal problems such as chronic diarrhea, and they can cause infections in many parts of the body. Some are deadly, like the Legionella bacterium, while others are relatively benign, especially if treatment can be accessed. One of the biggest problems in the developing world is the proliferation of treatable bacterial infections which run unchecked through populations due to lack of access to medications and medical treatment.

Treatment of an infection with a pathogenic bacterium involves the use of antibiotics, drugs which have been specifically formulated to kill bacteria. Some bacteria have developed antibiotic resistance, which means that they may not respond to many common antibiotics. This forces drug companies to research new antibiotics so that they can stay ahead of bacterial mutations.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a The Health Board researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By anon995107 — On Apr 03, 2016

I would like to arrange a study of the host relationship of the STD responsible strains.

By googlefanz — On Oct 05, 2010

So what would be some pathogenic bacteria diseases? I mean common ones, that anybody could get from your run of the mill bathroom doorknob pathogens.

By pharmchick78 — On Oct 05, 2010

@rallenwriter -- From what I remember from my bacteria lessons, I'll give your question a shot.

OK, doctors have several methods of identifying pathogenic bacteria. One of the primary ones, as you said, is a gram stain. A gram stain is usually the first step when it comes to identifying bacteria, as most bacteria are either gram positive or gram negative, depending on the chemical makeup of their cell walls.

Gram positive bacteria show up as purple, and gram negative bacteria show up as pink. This is usually the "go to" method for on the spot bacteria identification, since it's a lot quicker than a culture. However, this method is not foolproof, since some bacteria are gram-variable, and can show up either way. Some bacteria that you might recognize that are gram positive are staph, strep, and listeria.

There are additional steps that you can take to identify bacteria, usually by their characteristics. For example, thermophilic bacteria flourish in hot areas, so if a culture really explodes when you warm it up, that's another clue as to what your bacteria is.

Likewise, psychrophilic bacteria like it cold, so if your petri dish goes crazy when you put it in the refrigerator, that's another indicator of what your bacteria could be.

So although that's really basic, I hope that helps you out. At least next time you'll know what they're talking about next time you hear a TV doctor spout out "It's a non-pathogenic gram negative bacteria!"

By rallenwriter — On Oct 05, 2010

Can you tell me how doctors identify pathogenic bacteria? I know that pathogenic bacteria have characteristics that so called "friendly" bacteria don't have, but how exactly does the identification process work?

I know on TV shows they always talk about a gram stain, for instance, you'll hear a doctor say something about "gram negative pathogenic bacteria", but what exactly does that mean?

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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