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A microbe is a microorganism, more specifically a bacterium. There are different types of microbes: bacteria, archaea, fungi. protista, and viruses. These different types of microbes all exihibit similarities and differences and their own unique characteristics. Microbes affect every aspect of life on earth. They are amazingly diverse and can exist in a wide range of habitats; many of which live in or on the bodies of animals and plants. [1]
 

Microbial activity is exploited for the benefit of humankind in many ways, such as:

  • production of medicines 

  • production of food

  • production of enzymes

  • exciting advances resulting from developments in molecular biology techniques
     

It is important to remember that:

  • A pathogen is a micro-organism that has the potential to cause disease.

  • An infection is the invasion and multiplication of pathogenic microbes in an individual or population.

  • Disease is when the infection causes damage to the individual’s vital functions or systems.

  • An infection does not always result in disease

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WHAT IS A MICROBE?

    

 

 

 

 

 

 

 

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Bacteriophages are viruses that infect bacteria. They are used in gene technology to transfer foreign DNA that has been spliced into their nucleic acid into bacterial cells. The bacteria then acquire the ability to carry out the function of that particular gene and make specific proteins. 

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Examples of virus caused diseases in humans are measles, chicken pox, AIDS, and Ebola. [7]

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Viruses

Viruses are different from other microbes. Viruses:
  • are very small and can only be seen under an electron microscope
  • have no cellular structure
  • can only multiply inside the living cells of animals, plants
    or other microbes. This process harms the host, resulting
    in a disease. Outside of the host they are inert particles 
    called virions.
Structure of a virus. [5]

Archaea

Archaea used to be considered bacteria, but published studies and research demonstrate that they have some differences. For example, archaea have a different cell wall structure than bacteria, allowing for antibiotic resistance. [3]

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The 3 main types of archaea are as follows: 

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  • Crenarchaeota: They are able to live in extreme acidity and temperatures

  • Euryarchaeota:They produce methane and thrive off of salt

  • Korarchaeota: Not much is known about this type.

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Bacteria

Bacteria are microscopic unicellular organisms that are all around us. They come in many different sizes and shapes, and this is a common way to classify them—by their morphology. Populations of microbes (such as bacteria and yeasts) inhabit the skin and mucosal surfaces in various parts of the body. Vital to human health, bacteria provide the nutrients needed to sustain life by aiding in digestion, and contributing to regulation of appetite and the immune system. [2]

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Common types of bacteria are as follows:

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Coccus

Cocci are round, spherical bacteria. They may be single bacteria or they may occur in pairs, chains or clusters of bacteria, depending on the bacterium and environmental conditions. Cocci can cause many different common illnesses like pneumonia, meningitis, and strep throat.

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Bacillus
Bacilli are rod-shaped bacteria that occur singly or in linked chains. Bacilli can be arranged in different forms such as: 

  • Coccobacillus: combination with coccus

  • Diplobacilli: pairs

  • Palisades:V-shape attachment

  • Streptobacilli: chain

 

Spirillum​
Spirillum are large, elongate, spiral shaped, rigid cells that are usually found in freshwater.

An example of a spirillum bacteria is Campylobacter jejuni, the cause of foodborne illness and diarrhea. Campylobacter is among the most common causes of diarrheal illness in the United States. 

Diagram differentiating the shape and arrangements of bacteria. [1]

Protista

Unlike bacteria, Protista are eukaryotic; hence, their DNA is enclosed in a nucleus inside the cell. Scientists believe protists paved the way for the evolution of early plants, animals, and fungi. These are also parasitic organisms which live in the cells of other large organisms. Some of the examples coming under protista include: amoeba, Paramaecium, sporozoa, and Euglena.

 

Protists fall into three general subgroups: molds, unicellular algae, and protozoa.

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Molds

Molds are fungus or saprophytic organisms that live on the dead and the decaying matter. They are divided into two types: slime molds and the water molds. These organisms obtain their food by feeding on other organisms. Usually molds are characterized by the presence of spores and are even visible to naked eye.

 

Water Molds are found in wet environments, especially in fresh water sources and near the upper layers of moist soil, they are also known as downy mildews and white rusts. Water molds produce fungi-like filamentous hyphae, and feed on decaying tissue like rotting logs and mulch. 
 

Slime Molds exist as masses of cytoplasm, similar to amoebae. It moves over rotting logs or leaves and feeds by phagocytosis. The amoeba stage is called the plasmodium, which has many nuclei.

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Algae:

Most unicellular algae live in water, and other aquatic settings like in moist soil, and others join with fungi to form lichens. Similar to plants, algae can turn sunlight into energy. Algae cells contain light-absorbing chloroplasts and produce 75% or more of the oxygen in Earth's atmosphere along with cyanobacteria. Usually the algae are of six types namely green algae, brown algae, red algae, diatoms, pyrrophytes and euglenoids. All of these exhibit a unique character among them. Few examples of Algae are Volvox, netrium, Spirogyra and etc. [5]

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Protozoa: 

Protozoa are non-phototrophic, unicellular, microorganisms with no cell walls. Protozoa have been found in almost every kind of soil environment and have different intracellular organelles. [6]

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Blepharisma japonicum, a free-living ciliated protozoan. [4]

Image of protista. [3]

Fungi

Fungi are eukaryotic organisms. For instance, yeasts are present in our gut and on human skin. Fungi perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange in the environment. Since the 1940s, fungi have been used for the production of antibiotics, and, more recently, various enzymes produced by fungi are used industrially and in detergents. 

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Saccharomyces cerevisiae (baker's yeast), is also used to make bread and other wheat-based products, such as dough. Yeast species of the genus Saccharomyces are also used to produce alcoholic beverages like wine through a process called fermentation. [4]

Graphic showcasing fungal diversity present on the human skin. [2]

TYPES OF MICROBES

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