Bacteria definition
Bacteria Definition

Bacteria Definition, History, 9 Characteristics, Classification, and Identification

When hearing the word “bacteria”, most of you must immediately identify it with something dangerous. Yes, bacteria do have a bad reputation, and this is not without reason. Bacteria are the brain of various serious diseases. Ranging from pneumonia, typhus, tuberculosis, to meningitis. But bacteria don’t actually do any harm.

There are also types of bacteria that are good for health. Let’s get to know more about bacteria and other facts so you no longer misunderstand them.

Bacteria Definition

Bacteria are microscopic organisms that are invisible to the naked eye. They can live in diverse environments, both inside and outside the human body (such as land, river water, and seawater). Bacteria are thought to be the first ancient organisms to inhabit the earth, which was about four billion years ago.

History of discovery of bacteria

After knowing the Bacteria definition, here are The history of discovery of bacteria.

The first bacteria were discovered by Anthony van Leeuwenhoek in 1674 using his own microscope. The term bacterium was introduced later by Ehrenberg in 1828, derived from the Greek βακτηριον which means small stick.

Bacteria are divided into two subkingdoms, namely Archaebakteria and Eubacteria. The difference between subkingdom of archaebacteria and eubacteria is the composition of its ribosomes RNA.

Subkingdom eubacteria is a whole member of bacteria other than archaebacteria. Eubacteria is often considered a real bacterium.

Eubacteria are divided into three divisions, namely Graciliates, Firmicutes, and Tenecutes.

Bacteria characteristics

Bacteria have characteristics that distinguish them from other living creatures, namely:

  • Multicellular organisms.
  • Prokaryotes (does not have cell nucleus membranes)
  • It generally does not have chlorophyll.
  • It has a body size that varies between 0.12 to hundreds of microns.
  • Generally has an average size of 1 to 5 microns.
  • It has a diverse body shape.
  • Live freely, or parasites.
  • Who live in extreme environments such as hot springs, craters or peat.
  • The cell walls do not contain peptidoglycan.

Bacteria classification

To understand multiple groups of organisms, classification is required. Biochemical tests, gram coloring are effective criteria for classification. The coloring results reflect basic and complex differences in bacterial cells (cell wall structure), so that it can divide bacteria into 2 groups, namely Gram-positive bacteria and Gram-negative bacteria.

Gram-negative bacteria

Bacteria definition and classification
Bacteria Definition, History, 9 Characteristics, Classification, and Identification 2

Stem-Shaped Gram Negative Bacteria (Enterobacteriacea).

Gram-negative bacteria in the form of stems, their habitat are the intestines of humans and animals. Enterobacteriaceae includes Escherichia, Shigella, Salmonella, Enterobacter, Klebsiella, Serratia, Proteus). Some organisms such as Escherichia coli are normal flora and can cause disease, while others, such as salmonella and Shigella are common pathogens for humans.

Pseudomonas, Acinobacter and Other Gram Negative Bacteria.

Pseudomonas aeruginosa is invasive and toxic, resulting in infection in patients with decreased endurance and it is an important nosocomial pathogen.

Vibrio Campylobacter, Helicobacter, and other related bacteria.

These microorganisms are gram-negative stem-shaped species that are widespread in nature. Vibrio was found in both aquatic areas and water surface areas. Aeromonas is found in fresh water and sometimes in cold-blooded animals.

Haemophilus, Bordetella, and Brucella

Gram negative Haemophilus influenzae type b is a pathogen for important human beings.

Yersinia, Franscisella and Pasteurella.

The shape of a short Gram-negative stem is pleomorphic. The organism is catalyzed positive, oxidase positive, and it is a facultative anaerobic bacterium (Jawetz, 2004).

Gram-positive bacteria

Gram-positive spores-forming bacteria: Bacillus species and Clostridium.

Both species are everywhere, forming spores, so they can live in the environment for many years. Bacillus species are aerobic, while Clostridium is anaerobic obligate.

Non-Spore-Forming Gram-positive Bacteria: Species of Corynebacterium, Listeria, Propionibacterium, Actinomycetes.

Some members of the genus Corynebacterium and the Propionibacterium group are normal flora of the human skin and mucous membranes.


Round in shape, it is usually arranged in irregular clusters such as grapes. Some species are normal flora members of the skin and mucous membranes, others cause suppuration and even fatal septicemia.

Pathogenic staphylococcus often hemolysis the blood, coagulates plasma and produces a variety of extracellular enzymes. Medically related staphylococcus types are Staphylococcus aureus, Staphylococcus epidermidis and Staphylococcus saprophyticus.


It is a round gram-positive bacteria that have a partner or chain in its growth. Some streptococcus is normal human flora, but others can be pathogenic in humans. There are 20 species in between; Streptococcus pyogenes, Streptococcus agalactiae, and Enterococcus type (Jawetz, 2004).

Bacteria identification

Bacteria have a variety of different characteristics, therefore in the process of studying and understanding bacteria in a particular group is required identification.

Identification is done by looking for traits in organisms that are not yet known then compared to known organisms. The identification of recently isolated microorganisms requires very detailed, and clear details, descriptions, and comparisons with previously published descriptions for other microorganisms of similar species (Pelczar & Chan, 1989).

Bacterial identification can be done in two ways, either morphologically or physiologically, morphological identification can include colony shape, colony structure, cell shape, cell size, and bacterial coloring.

Morphological observations can then be further divided into two, namely macroscopic and microscopic observations, macroscopic safeguards are carried out by observing microorganisms in visible and visible parts of the naked eye, such as colony shape, colony edges, colony elevation and colony surface (Cappucino & Sherman, 1987).

While microscopic observations are used when observing movement, and division binary, observing the natural shape and size of cells, which during heat fixation and during the coloring process resulted in some changes.

Physiological observations can be done with biochemical tests,
Physiological observations can be done by means of testing such as carbohydrate fermentation, Methyl red testing, Vogest Paskauer testing, oxidase testing, protease testing and others (Cappucino & Sherman, 1987).

Thank you very much for reading Bacteria Definition, History, Characteristics, Classification, and Identification, hopefully useful.

Last Updated on February 25, 2021 Reviewed by Market Health Beauty Team

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