Microorganisms

The first form of life to develop on Earth were single-celled microorganisms. These organisms are so small that they are visible only through a microscope. They exist as a single cell or a cluster of cells. Between 1665-1683, two biologists from The Royal Society, Robert Hooke, and Antonie Van Leeuwenhoek discovered the existence of microorganisms. All unicellular organisms like protozoans, bacteria and some algae are included under the category of microorganisms and are largely diverse.

Microorganisms are omnipresent, they are found everywhere. They live in every nook and corner you could possibly imagine. On your seat, under the table, over the roof, even on your body parts, your palms, literally everywhere. They also dwell in extreme weather conditions like the equator, poles, deserts, ice-cold water bodies, hot boilers etc and adapt accordingly.

Microbes Definition

“Microbes are single-celled organisms that are invisible to the naked eye.”

What are Microbes?

Microbes are minute, unicellular organisms that are invisible to the naked eye. They are also known as microorganisms or microscopic organisms as they could only be seen under a microscope. They make up almost 60% of the earth’s living matter. 

The term “microbes” is used to describe several different life forms with different sizes and characteristics. A few of these microbes include:

• Bacteria
• Fungi
• Protists
• Viruses
• Archaea

Microbes can be useful as well as harmful. Certain microbes cause severe infections and diseases and can also spoil food and other materials. While others play an important role in maintaining environmental balance.

Let us have a detailed look at the different types of microorganisms and their importance.

Types of Microbes

The different types of microorganisms are:

Bacteria

• Bacteria are unicellular, microscopic, prokaryotic microorganisms that contain no true nucleus.
• Their cell wall is made up of peptidoglycan. They have a flagellum that facilitates locomotion.
• Bacteria are of different types depending on their shapes and sizes. E.g., spherical-shaped bacteria are known as cocci; rod-shaped bacteria are known as bacilli; spiral-shaped, spirilla, etc.
• They reproduce through binary fission, transfer of genetic material occurs through transformation, transduction and conjugation, and through sporulation.
• Bacteria play an important role in human survival. They break down nutrients in the digestive system into simpler forms.
• Few bacteria such as Rhizobium are involved in nitrogen fixation.
• They are also used for making antibiotics and can also be used in agriculture as biopesticides.

Fungi

• These can be unicellular or multicellular with the cell wall made of chitin.
• These are heterotrophic and cannot synthesise their own food.
• They comprise membrane-bound organelles.
• Yeasts, moulds, mushrooms are some of the important fungi.
• They decompose dead plants and animals, extracting nutrients from them.
• Few fungi are harmful and cause fungal infections like ringworm. The others are used in making antibiotics like penicillin.
• Fungi such as yeast are used in the baking industries and also in the beer and wine industries.

Viruses

• Viruses are a connecting link between living and non-living.
• They are non-cellular microorganisms, composed of protein, nucleic acids, and lipids.
• They are measured in nanometers with sizes ranging from 20 nanometers to 250 nanometers and could only be seen with an electron microscope.
• They contain the core of nucleotides surrounded by a protein coat which could invade living cells.
• They are active inside host cells and reproduce inside them by infecting living cells.

Protists

• These are unicellular, microscopic organisms that are neither plants nor animals.
•  They may be autotrophic or heterotrophic.
• They reproduce mainly through binary fission or budding.
• This group includes plant-like protists such as diatoms, dinoflagellates, animal-like protists such as amoeba, and fungus-like such as slime moulds.
• Protists supply us with oxygen and recycle crucial nutrients to make it available to other life forms.

Archaea

• These are unicellular prokaryotic organisms and have a structure similar to bacteria.
• Their cell wall is different from bacteria and contains unique lipids that enable them to survive in extreme conditions.
• They are also found in human gut and skin.

Any entity that possesses characteristics of life such as the ability to reproduce, respond to environmental stimuli, constitutes a living organism. Furthermore, living organisms need sustenance to survive, hence they need to eat. Also, movement and mobility is a crucial aspect of an organism if it needs to acquire food.

Most organisms are visible to us. But some living organisms are extremely small, so a microscope is required to view them. These organisms are known as microbes or microorganisms and are single-celled or unicellular. They exist in nature in almost every habitat. They are ubiquitous.

Microorganisms are crucial in maintaining a balance in our ecological system. They live around us and inside us. They maintain the health of organisms and help clean up our environment. They help produce different foods too.

While microorganisms have tons of benefits they can be harmful and cause deadly diseases too. For example, we see fungus growing on bread when left unused for a couple of days. This is because bread is moist, making it one of the most favourable conditions for the breeding of microbes.

Classification of Microorganism

Microbes are categorized into four major groups:

• Bacteria

• Fungi

• Algae

• Protozoa

Viruses, on the other hand, are microscopic but differ from microbes. Differ in their reproduction aspects, as they reproduce only in the cells of their hosts. These host organisms can be of animals, bacteria or even plants for that matter. A virus is typically coated by protein and has a nucleic acid molecule.

Classification of Microorganisms

All organisms that are very small or microscopic in size, and cannot be seen with the naked eye are referred to as microorganisms. Microorganisms are visible under the microscope. Anton van Leeuwenhoek first observed microorganisms under the microscope. Microorganisms include bacteria, archaea, algae, fungi, protozoa, etc. Although viruses are not considered living organisms, sometimes they are also included in the microorganisms category.

Classification is the process by which organisms are grouped into various categories based on morphological and physiological characteristics. There have been various attempts to classify organisms based on their morphological, physiological, cellular and molecular characteristics. Modern classification is also based on evolutionary relationships i.e. phylogenetic relationships.

Microorganisms are prokaryotic, such as bacteria, archaea,etc., as well as eukaryotic, such as protozoa, algae, fungi, etc. R.H. Whittaker elucidated the Five Kingdom Classification, which was based on the following characteristics:

• Cell type (prokaryotic and eukaryotic) and presence of nuclear membrane
• Presence of cell wall and its constituents
• Body organisation
• Mode of nutrition
• Mode of reproduction
• Phylogenetic relationships

Based on the following characteristics, R. H. Whittaker divided living organisms into five kingdoms. They are as follows:

1. Monera – Unicellular prokaryotes
2. Protista – Unicellular eukaryotes
3. Fungi – Eukaryotic, heterotrophic (saprophytic/ parasitic) and with a cell wall (chitin)
4. Plantae – Eukaryotic, autotrophic (photosynthetic) and with a cell wall (cellulose)
5. Animalia – Eukaryotic, heterotrophic (holozoic/ saprophytic etc.) and without a cell wall

Let’s learn more in detail about the classification of microorganisms based on the Five Kingdom Classification.

Prokaryotic microorganisms include bacteria, cyanobacteria or blue-green algae, archaea, mycoplasma, etc. Eukaryotic microorganisms include protists, protozoans, slime moulds, algae, fungi, etc.

Bacteria (Monera)

As per the Five Kingdom Classification, bacteria are classified in the kingdom Monera. It includes Eubacteria and Archaebacteria. They are all unicellular, have a prokaryotic cell which is devoid of a membrane-bound nucleus, and other organelles such as endoplasmic reticulum, mitochondria, Golgi bodies, etc.

Later, archaebacteria were placed into a different domain of the three-domain system, i.e. Bacteria, Archaea and Eukarya.

Bacteria are the most abundant microorganisms and are present almost everywhere. They are classified as Gram-positive and Gram-negative, based on the Gram’s staining pattern.

Based on the shape of the cell, bacteria are classified into four main groups that are as follows:

• Coccus or cocci (spherical)
• Bacillus or bacilli (rod-shaped)
• Spirillum or spirilla (spiral)
• Vibrium or vibrio (comma-shaped)

Eubacteria

They are true bacteria. They have a rigid cell wall and may contain flagella. They are autotrophic as well as heterotrophic. Bacteria reproduce by binary fission and DNA transfer. Some bacteria produce spores under unfavourable conditions. Mycoplasma does not contain a cell wall.

• Photosynthetic autotrophs: This includes blue-green algae or cyanobacteria. They contain chlorophyll ‘a’ similar to green plants, and perform photosynthesis. Some cyanobacteria are also capable of fixing atmospheric nitrogen. E.g. Nostoc and Anabaena.
• Chemosynthetic autotrophs: These microorganisms utilise energy derived from the oxidation of inorganic substances such as nitrates, ammonia, sulphur, etc. and produce ATP. These organisms play an important role in nutrient recycling. E.g. purple sulphur bacteria.
• Heterotrophs: They are widely distributed and play a key role in the ecosystem as decomposers. They play a significant role in our lives. They are used for the industrial production of antibiotics, organic acids, etc. They also act as nitrogen-fixers, e.g. Rhizobium in the root nodules of legumes. Some bacteria are pathogenic to plants and animals causing various diseases, e.g. cholera, tuberculosis, typhoid, botulism, tetanus, citrus canker, fire blight of apple, etc.

Archaebacteria

They can thrive in extreme environmental conditions. They have different cell wall compositions, which enable them to survive in harsh conditions. The cell membrane of archaea is ether-linked as compared to ester-linked in bacteria. They are further classified into three main groups:

• Methanogens – They are found in marshy areas. They are found in the gut of many ruminating animals and are utilised for the commercial production of methane (biogas).
• Halophiles – They are found in extreme salty areas.
• Thermoacidophiles – They can tolerate extreme temperatures and low pH. They are found in hot springs.

Protozoa

In the Five Kingdom classification, protozoans are classified under the kingdom Protista, which includes unicellular eukaryotes. Protozoans are heterotrophs. They live as parasites or predators.

On the basis of their mode of locomotion, they are classified into four major groups. They are:

• Amoeboid – They have pseudopodia, which is used for movement and capturing prey. E.g. Amoeba, Entamoeba, etc.
• Flagellated – These protozoans are flagellated. They are either free-living or parasites. E.g. Trypanosoma, the causative organism of sleeping sickness, Leishmania, which causes kala-azar, etc.
• Ciliated – They are aquatic and have thousands of cilia present on the body surface, e.g. Paramoecium. Cilia also help in bringing water laden with food inside the cavity of the gullet.
• Sporozoans – They are non-motile. They produce spores. E.g. Plasmodium, the causative organism of malaria, Toxoplasma, etc.

Slime Moulds

Slime moulds are also protists. They are saprophytes. They often form aggregates called plasmodium. They form spores that are extremely resistant to adverse conditions. Slime Moulds move along dead and decaying branches and leaves, and absorb organic compounds.

Fungi

Fungi are separated into a different kingdom. They are heterotrophic and have a rigid cell wall. They are parasites or saprotrophs. Fungi are microscopic, as well as quite big in size. They are cosmopolitan and grow in warm, humid places. A unicellular fungi – yeast, is used for the industrial production of bread and alcoholic beverages. Penicillium is used for the production of antibiotics. Some fungi cause diseases in plants and animals, e.g. wheat rust (Puccinia), Candida albicans causing fungal infection in humans.

Fungi are classified into four main classes based on their morphology and method of spore formation. They are:

• Phycomycetes – They are characterised by the presence of coenocytic mycelium. Spores are produced endogenously in the sporangium, e.g. Rhizopus, Mucor, etc.
• Ascomycetes – They are commonly known as sac-fungi. The mycelium is branched and septate. The asexual spores are produced exogenously on conidiophores and sexual spores are produced endogenously within asci. E.g. Penicillium, Saccharomyces (yeast), Aspergillus, Claviceps and Neurospora, etc.
• Basidiomycetes – Asexual spores are not formed. The basidiospores are exogenously produced. E.g. Puccinia (rust), mushrooms, Ustilago (smut), etc.
• Deuteromycetes – Commonly called imperfect fungi due to absence of sexual stage in the life cycle. Most fungi are decomposers and help in nutrient recycling. E.g. Colletotrichum, Alternaria and Trichoderma.

Algae

Unicellular photosynthetic organisms like diatoms, golden algae and dinoflagellates are placed under the kingdom Protista. They are microscopic and are plankton. They are photosynthetic and chief producers in the sea.

• Diatoms – They have a silicious cell wall which fits like a soap box. They are photosynthetic and ‘diatomaceous earth’ is used for polishing, filtration of oil, etc.
• Dinoflagellates – They are marine, and photosynthetic and appear in different colours. They have two unequal flagella, one longitudinal and one transverse. The cell wall has stiff cellulose plates. They are known to cause red tides due to rapid multiplication, e.g. Gonyaulax (a red dinoflagellate).

Algae are placed in the kingdom Plntae. Algae vary in size and shape. They are unicellular or multicellular. Some green algae are microscopic in size, and many form colonies. Algae are classified based on the presence of pigment present in them:

• Chlorophyceae – Green algae. They have chlorophyll a and b pigments. Some green algae are microscopic. E.g. Chlamydomonas, Volvox, Ulothrix, Spirogyra. Chlamydomonas is a unicellular green alga. Volvox forms coenobium or a colony of thousands of cells.
• Phaeophyceae – Brown algae. They have chlorophyll a and c, and fucoxanthin pigments.
• Rhodophyceae – Red algae. They have chlorophyll a and d, and phycoerythrin pigments.

Uses of Microorganisms

As discussed, microorganisms are beneficial for humans in various ways. They play an important role in human welfare and for the environment. These include processing and preservation of food,  production of biomolecules, manufacture of pharmaceutical products, cosmetics industries, recycling the nutrients in the soil and so on. Listed below are some of the applications of microorganisms in human welfare.

Making Of Curd And Bread

The curd is obtained by the action of bacteria on milk. A bacterium named Lactobacillus is present in the milk, which promotes the formation of curd by multiplying itself continuously in milk. Bacteria are involved in the making of:

• Cheese
• Pickles
• Yeast and bacteria are important in the fermentation of dosa and idli batter

Yeast is used extensively in the baking industry to make pastries, cakes etc. They do so by continuously reproducing and as they respire they produce carbon dioxide as a result of which dough increases in size due to bubble formation.

Commercial Use Of Microorganisms

Microorganisms such as yeast are grown on natural sugars to produce alcohol, wine, and vinegar on a large scale. Fermentation is the process of converting sugar into alcohol. Yeasts take part in fermentation.

Medicinal Use Of Microorganism

Microorganisms are the primary source of making antibiotics. Antibiotics are medicines that stop or inhibit the growth of disease-causing microorganisms. Antibiotics are produced by growing many fungi and bacteria and are used to treat numerable diseases. Few antibiotics are:

• Erythromycin
• Amoxicillin
• Streptomycin

In animals, antibiotics are used to check microbial infections. They are used in plants to control diseases as well.

Vaccine

On a large scale, vaccines are manufactured using microorganisms to protect animals and humans from various diseases. Diseases such as smallpox, hepatitis, tuberculosis can be 

Food Industry and Beverages

The role of microorganisms in food preparation and beverage manufacturing is known for ages. They are used in the manufacture of bread, curd, wine, and alcohol etc. Lactobacillus bacteria are responsible for the curd formation. They multiply and convert milk into curd. Another example is Yeast which is used commercially for alcohol and wine production. The process is called fermentation. Yeast is also used in baking industries for the preparations of bread and cakes.

Micro-flora

Bacteria are not only present outside the human body, but they also live inside the body too. This aggregate collection of microorganisms that is present in the human body is termed as Microflora.

Bacteria are also present in the gut, and they aid the process of digestion by releasing certain enzymes. They live in a symbiotic relationship with a human. Other roles of microflora are vitamin K production, which is crucial in enabling blood clotting. They also prevent the invasion of the foreign bodies, by acting against other fatal microbes.

Pharmaceutical Industry

Antibiotics go hand in hand with microbes in the medical field. Typically, antibiotics are obtained from a weakened form of an otherwise harmful microorganism. This is then injected into the body and the body learns to fight off the diseases caused by these organisms. Examples of this include mumps and the measles.

Environment

In the environment, microorganisms have two vital roles- one is an enhancement of soil fertility another is cleaning. Azotobacter, Rhizobium, Clostridium are few examples of Nitrogen-fixing bacteria which play a primary role in transforming atmospheric nitrogen into inorganic compounds which are then used by the plants. Without this process, the vast majority of the nitrogen present in the atmosphere becomes unusable.

Microorganisms also act as cleaners. Plants and animals eventually die and their bodies are turned into nutrients which the environment can use.

Useful Microorganisms

Following are a few examples of useful microorganisms:

• Extensively used in the baking industry to make cakes, bread, pastry etc.

• Used in the production of milk products. Example: Lactobacillus bacteria is used in the formation of curd from milk

• Since ages, microbes are being used in the production of alcohol

• It is also used to make organic acids. Acids such as citric acid, lactic acid, fumaric acid, gluconic acids are made using microbial activity

• Used in the production of steroids

• Antibiotics are produced using microorganisms

• Used in the production of vitamins: Vitamins such as Vitamin B complex, Riboflavin is produced by Ashbya gossypii, Eremothecium ashbyii and Clostridium bytyricum. Ascorbic acid, also known as Vitamin C is produced by species of Acetobacter

• Microorganisms synthesize enzymes such as Lipase, Lactase, Amylase, Pectinase, Penicillinase.

• They increase the fertility of the soil and by fixing nitrogen

• Help in the treatment of sewage

• Extensively used to clean up our environment

• Used in pest control

The Role Of Microbes In Industrial Products

Industrial microbiology is a branch of biotechnology and microbiology, which mainly deals with the study of various microorganisms and its applications in industrial processes.

In large-scale industrial processes, microbes are widely used to synthesize a number of products valuable to human beings. There are numerous industrial products that are derived from microbes such as:

• Food additives.
• Alcoholic and non-alcoholic beverages.
• Biofuels, metabolites, and biofertilizers.
• Few Chemicals, Enzymes and other Bioactive Molecules.
• Vaccines and other Antibiotics to kill or retard the growth of disease-causing microbes.

Let us know in detail about the role of microbes in industrial products.

Microbes in Industrial Products

These microbes play a crucial role in the fermentation process to obtain a number of products. The two common products obtained by fermentation process through industrial processes are fermented beverages, malted cereals, broths, fruit juices, antibiotics, etc.

Beverages

Yeasts are the widely used microorganism for the production of beverages like beer, brandy, rum, wine, whiskey, etc. Yeasts are single-celled, eukaryotic, microorganisms of the Kingdom Fungi. In these industrial process, the species of yeasts, Saccharomyces cerevisiae, generally called as the Brewer’s Yeasts are used for fermenting fruit juices and malted cereals to produce ethanol. Once after the fermentation, these beverages are distilled to produce both Alcoholic and non-alcoholic beverages including whiskey, brandy, rum, etc.

Organic acids

Microbes are also used for the industrial production of certain organic acids. Citric acid was the first discovered organic acids from microbial fermentation of lemon – a citrus fruits. Organic acids are also produced directly from glucose. Aspergillus Niger, Acetobacter acute and Lactobacillus are few examples of microbes used for the industrial production of organic acids.

Enzymes

Enzymes are naturally occurring, biological catalysts that are mainly used to control certain biochemical reactions in the living system. Enzymes have a wide range of applications in the production of both medical and non-medical field. Apart from the plants and animals, enzymes are also obtained from certain microbes and are referred to as the microbial enzymes. Microorganisms are majorly used for the production of industrial enzymes through the safe gene transfer methods. The first industrially produced microbial enzymes were obtained from the fungal amylase in the year 1896 and were used to cure indigestion and several other digestive disorders. 

Antibiotic

Antibiotics are chemical substances produced by certain microbes which functions either by killing or retarding the growth of harmful microbes without affecting the host cells. Penicillin was the first antibiotic to be discovered by Alexander Fleming in the year 1928 from the fungus Penicilliumnotatum. There are many other antibiotics produced by microorganisms, including Streptomycin, and other antibiotics used to treat a number of bacterial infections.

Vitamins

Vitamins are organic compounds which are capable of performing many life-sustaining functions inside our body. They are essential micronutrients which are required in small quantities for the body’s metabolism. As our body cannot be synthesized these vitamins, they need to be supplied through the diet. Apart from plants and animals sources, microbes are also capable of synthesizing the vitamins. There are few groups of microbes living in the digestive tracts of both humans and other animals which are collectively called as the gut microbiota. These microbes are involved in synthesizing vitamin K. Other examples of microbial vitamins include ascorbic acid, beta-carotene, biotin, ergosterol, folic acid, vitamin b12, thiamine, pantothenic acid, riboflavin, and pyridoxine.

These were a few information related to the role of microbes in industrial products. Apart from these products, microbes are also used in the production of biofuel, vaccines, protein and other hormonal supplements to treat malnutrition and other deficiency diseases in both humans and animals.

Harmful Microorganisms

As we all know by now, there are organisms that are extremely small and can’t be viewed without the help of a microscope. Some microorganisms are not harmful, in fact, some are quite helpful (like the bacteria that is found in your gut). But a majority of them cause a lot of diseases in man and other organisms. Microorganisms include bacteria, algae, fungi, archaea, and protozoa. Even though viruses are very small and cause diseases, they are not technically classified as a microorganism as they are not considered to be “alive.”

Most of the microorganisms that we know are free-living, while others are parasites. Let’s take a glance at harmful microorganisms around us.

Harmful Microorganisms

Except for genetic and congenital factors, most of the diseases are caused by certain microorganisms. These microbes are called pathogens. They are specially adapted to infect and multiply within a host. Some diseases caused by pathogens are polio, cholera, mumps, rabies, malaria etc.

Some microorganisms need a carrier to transmit diseases. Here, Anopheles mosquitoes are the carriers used by the protozoan Plasmodium vivax to transmit the disease to the host. Once inside the host, the Plasmodium starts destroying red blood cells. This leads to other complications such as anaemia and hypoxemia.

Other microbes directly enter the body through contaminated food, water, air or even just a small cut on your skin. The bacteria, Streptococcus can enter your skin through an open wound. However, these bacteria are found in most people’s throat and are relatively harmless. But sometimes, the infection can be so severe that it can start eating living flesh and tissue. That’s why it’s also called “Flesh-eating bacteria” or “Necrotizing fasciitis.”

Most of the pathogenic diseases are communicable and infectious. Once pathogens enter the host body, they utilize the host nutrients; also invade the immune system of the host. This led to the discovery and development of antibiotics and vaccines.

Microorganisms are specific to their host. Some diseases affect only animals like Anthrax, but they can be transmitted to human also. Some diseases like Crown gall disease infect plants by certain bacteria and viruses. The diseases affecting animals and plants can decrease the quality and yield of the product and may lead to investment loss. Therefore, it is necessary to control microbial growth.

Harmful microorganisms not only damage the human body, but also the food we eat. Sometimes, they multiply on food and release toxic products, hence cause food poisoning. To avoid food poisoning, food preservation is done in various ways like pasteurization, salting, boiling etc.

In conclusion, microorganisms are all around us. From the chair that we sit to the keyboards that we type, our environment is home to billions of microscopic organisms. Moreover, we even have microbes living in our gut that play an important role in our digestive health. In other words, most microorganisms are not harmful, but we have to take precautions against the ones that are.

Harmful Microorganisms

• The microorganisms that cause diseases in living beings are known as pathogens.

• The pathogens can enter our bodies through air, water and food.

• Some pathogens are transmitted directly from an infected person.

• The diseases which are transmitted by an infected person directly or indirectly are known as communicable diseases. For eg., common cold, tuberculosis, etc.

• Microorganisms also grow on food and spoil it. That is why preservatives are added in the food to prevent it from spoilage.

• Food Spoilage by Microorganisms

  1. Food spoilage refers to the damage in the quality of food that makes it unsuitable for human consumption.
  2. Bacteria, moulds, and yeast are the main causes of food spoilage.
  3. Moulds spoil food with reduced water activity. For eg., dry cereals, cereal products.
  4. These microbes produce certain enzymes that decompose the important constituents of food.
  5. Bacteria, on the other hand, cause the spoilage of food with increased water activity. For eg., milk products.

Microbes And Disease

Microbes or microorganisms are minute, unicellular organisms that cannot be seen by naked eyes. Some microbes are useful in our day to day life while others are harmful to our health. The harmful microorganisms are called pathogens.

The diseases causing microorganisms include bacteria, viruses, protozoa, fungi and a few variations of worms. Once they invade the host cell, they disrupt or damage the normal cellular activities. This leads to diseases on a larger scale.

Disease-causing Microbes

Diseases Caused By Microorganisms

There are several diseases caused by microorganisms. Let us have a look at a few of them.

• Viral diseases are caused by viruses. These include both acute and infectious diseases like the common cold, to chronic disease like AIDS.  Apart from these acute diseases, viruses are also responsible for mumps, polio, rabies etc.
• Diseases caused by bacteria include diphtheria, typhoid, cholera etc.
• Malaria and sleeping sickness are diseases caused by protozoa.
• Worms like roundworms, tapeworms could cause diseases like Ascariasis and Taeniasis respectively.

The microorganisms cause diseases in the following ways:

• They reach their target site in the body.
• Multiply rapidly.
• Attach to the target site to be infected.
• Avoid and survive an attack by the immune system of the host.
• Obtain nutrients from the host.

Microbes and Diseases

Viruses

Viruses can be seen only through an electron microscope. They are inactive outside a living cell. Once they are inside the host body, they take over the entire cellular activities of the organism. They cannot be destroyed by antibiotics. Common cold, measles, mumps, smallpox are some of the diseases caused by viruses.

Bacteria

Not all bacteria cause diseases. The bacteria that infects an organism produces toxins that can cause diseases. Cholera, tuberculosis, anthrax are caused by bacteria. These can be killed by antibiotics.

Fungi

Fungi can grow in damp, moist areas on the body and lead to infections such as athlete’s foot, ringworm, etc.

Protozoa

Protozoans such as amoeba cause diseases such as amoebic dysentery. Malaria and sleeping sickness is also caused by protozoans.

Following is the list of microorganisms and infectious diseases caused by them:

Diseases	Microorganisms
Cold	Rhinovirus
German Measles	Rubella
Chickenpox	Varicella zoster
Whooping cough	Bardotella pertussis
Bubonic plague	Yersinia pestis
Ringworm	Trichophyton rubrum
Tuberculosis	Mycobacterium tuberculosis
Malaria	Plasmodium falciparum
Athlete’s foot	Trichophyton mentagrophytes

The sources and means of transfer of these infections are quite different. The sources through which the bacteria spread diseases is different from that of viruses. The main source of bacterial infection is contaminated food and water while viral diseases spread mainly through the air. Hence, bacterial and viral diseases are usually communicable. Other means of transfer of pathogens include direct physical contact i.e. blood transfusion, breastfeeding, sexual contact etc.

Microbes enter our body through different sites:

• Respiratory tract
• Urogenital tract
• Gastrointestinal tract
• Skin surface

Certain pathogenic diseases are organ or tissue-specific. For example, tuberculosis affects the lungs of the individuals while jaundice causing viruses target the liver.

Prevention

There is the quote, ‘prevention is better than cure’. Drugs like antibiotics or antibacterials are used to destroy or slow down the growth of bacteria. These antibiotics, however, are not effective for viral infections. The depth or severity of infection depends on the amount and rate at which microbes spread.

Diseases Caused By Microorganisms

Some diseases caused by microbes are:

Bacteria	Fungi	Protozoa	Virus
Tuberculosis	Ringworm	Malaria	Flu & Common cold
Typhoid	Athlete’s foot	Dysentery	Warts
Cholera	Candidiasis	Chagas disease	Polio
Plague	Tinea versicolor	Sleeping sickness	Herpes and cold sores
Meningitis	Onychomycosis	Intestinal protozoan disease	Chickenpox
Tetanus			Smallpox
Lyme disease			Ebola

Diseases Caused by Microorganisms in Animals

Diseases	Microorganism
Anthrax diseases	Bacillus anthracis
Foot and Mouth disease	Virus

Diseases Caused by Microorganisms in Plants

Diseases	Microorganism
Citrus canker	Bacteria
Rust of wheat	Fungi
Yellow vein mosaic of Okra	Virus

Some Interesting Facts About Microbes

• Microbes can be fatal.

• Microbes in our gut cause change of mood.

• Dry hands have fewer bacteria than damp hands.

• The smallest known bacteria is the Mycoplasma.

• 50% of the oxygen we breathe come from microbes.

• Your belly button alone has more than 1400 bacteria.

• There are more than a billion microbes in a person’s mouth.

• 1.82kgs of your body’s weight constitutes the collective weight of microbes in your body.

Important Questions on Microbes:

• Name the bacterium which is used in curdling of milk.

Lactobacillus bacteria.

• Which types of microbes are used to produce penicillin antibiotic?

The penicillin antibiotic is obtained from the fungus – Penicillium notatum.

• Name a bacterium that produces acetic and butyric acid.

Acetic Acid is produced by the bacterium  Acetobacter acetic and butyric acid are produced by the bacterium Clostridium butylicum.

• Name a bacterium that is present in the root nodules and fix atmospheric nitrogen.

Rhizobium is Gram-negative soil bacteria that fix nitrogen and helps plants to observe atmospheric nitrogen.