Disease Causing Microorganisms

We have heard time and again that we need to keep ‘germs’ away!

‘Germs’ are actually another word for microorganisms or microbes.

These can affect both plants and animals and cause diseases in them.

This is why we need to keep ourselves and surroundings clean. Let’s

read more about the disease causing microorganisms.

What are these ‘germs’?

They are small living organisms that are present everywhere- on us,

inside us and in our surroundings and cannot be seen with the naked

eye. Special devices called the microscope help us see and study them.

However, it is important to note that not all microorganisms are bad.

We can broadly classify these into ‘good’ and ‘bad’ microorganisms.

The ‘good’ microorganisms help in the routine body functions such as

digestion, immunity and coexist inside our body all the time. The

‘bad’ microorganisms are the ones that we need to stay clear of

because they make us fall ill by causing diseases.

In biology, disease-causing micro-organisms can be classified into

four main groups:

● Bacteria

● Virus

● Fungus

● Protozoa

These ‘bad’ micro-organisms or disease causing microorganisms are

always looking for a chance to enter our body and cause a disease.

Most diseases in the world are caused by these micro-organisms, for

example, the common cold and flu, malaria, diarrhoea, pneumonia,

urinary tract infections, chicken pox, Hepatitis, polio etc.

How do these disease causing microorganisms function in the human body?

Disease causing microorganisms outnumber our body cells in a large

way. They are present on the skin and various orifices of our body

through which they can enter into the system such as:

● Respiratory tract

● Genital Tract

● Urinary tract

Once these microbes enter the system, depending on their own

constitution, they look for their target site and attach themselves there.

Once they firmly attach themselves, they release toxins and enzymes

to stay grounded and at the same time start multiplying and increase in

number. The microbes derive nutrition from the host’s body. The

toxins and enzymes released by these microbes make the cells of the

host weak or ‘ill’ or affected. These toxins can even be spilt into the

bloodstream and reach other parts of the body which can also be

affected. This way the microbes are able to make the body they are in

sick! The manifestation of these toxins and enzymes released on the

tissues are varied such as inflammations, swellings, bleeding, wounds,

pustules, fever, sneezing, itching and general weakness in the body.

What does the host’s body do?

If you think the microbes have their way once they are in, then you are

wrong! The human body is designed to keep all disease-causing

elements out of it. The human body always has its defences up even

before the microbes enter. For this reason, keeping ourselves clean,

healthy and alert is essential. By doing so we do not allow close

contact with these microorganisms and so minimise their chances of

entering the system.

But, there are many times when the microbes enter the body and find

their favourite spot. In these cases, the body’s ‘immune system’

consisting of defence cells are activated. From the time of the

microbes entry into the body till the time the body fights it and its

products, the immune system is on high alert. The defence cells of the

body constitute mainly of two types of cells: T-Lymphocytes and B-

Lymphocytes. They both have a different sub-types and modes of

action. Together, they are responsible for eradicating the pathogen as a

whole either by engulfing it (phagocytosis) or releasing their remedial

toxins (antibodies) against the toxins and enzymes of the microbes.

Imagine it to be a battle-field between the disease causing pathogens

and the body’s armed forces -the T and B- Lymphocytes.

The end result depends upon whose defences are higher. A healthy

body which is well nourished is better equipped to fight a microbial

invasion compared to a not-so-healthy body. Therefore, it is essential

to stay fit. When the body isn’t able to fight back on its own, help is

given from outside in the form of antibiotics(for bacteria),

antivirals(viruses), antifungals(fungus) and anti-helminthic(protozoa).

These can be either in the tablet or capsule form or vaccinations.

Transmission

Microbes can be transmitted through different routes: few are

airborne, few are waterborne, some travel on top of other animals,

some are transmitted through human touch, some through touching

contaminated surfaces or objects and some though ingesting

contaminated water and food. Keeping clear of obvious contaminated

or infected areas is important.

In case of plants, there is a host defence mechanism that helps fight

these microorganisms as in the case of animals. But, the

microorganisms that affect plants and animals are very different.

Different species of bacteria, virus and fungi affect plants.

Disease causing pathogens are therefore present everywhere. Whether

they are able to enter our body and cause a disease is in our hands to a

large extent. Advances in medicine have been made to make our

body’s immune system stronger with preventive medicines and

vaccinations. There have been biotechnological advances to protect

plants as well from infestations and plant diseases.

Let’s do our bit daily to stay fit and healthy, as it is absolutely

essential.

Food Preservation

Food preservation is a process by which edible items such as fruits

and vegetables are prevented from getting spoilt. The nutritive value,

flavour and colour of the foods preserved remain intact.This is done to

increase the life of the food product and enable its storage and supply.

(Source: Wikipedia)

What principles is food preservation based on?

The main aim of food preservation is to prevent the food that is being

preserved from decay by microorganisms.

The principles it works on are:

1.Preventing microorganisms in the food that is being preserved i.e

maintaining asepsis.

2. Removal of microorganisms

3. Preventing or hindering the growth of microorganisms by various

methods such as low temperatures, drying, use of chemicals etc.

4. Killing the microorganisms by various methods such as heating and

radiation.

Some food substances can self-decompose due to the enzymes that are

present in them. In these cases, the enzymes are deactivated at the

time of food preservation.

Some foods are also susceptible to insects or animals and so the

utilisation of appropriate chemicals to kill them and prevent them

from destroying the food.

Let’s now look at the methods that are used for food preservation

Food preservation methods are broadly divided into three:

1. Biological

2. Physical

3. Chemical

The commonly used methods of food preservation fall into one of the

above categories. The main purpose of all these methods is to either

prevent or retard spoilage of food items.

1.Filtration

This is done for liquids such as juices. The process applies pressure

while the liquid is passed through a very fine sieve. This results in the

liquid passing through while the microbes cannot and thus the liquid

obtained is sterile.

2.Heat treatments

There are different kinds of heat treatments that can be done such as

boiling at 100 degrees Celsius, boiling above 100 degrees

Celsius(sterilisation)or pasteurisation( as done in case of milk)

3. Low- temperature treatments

The most commonly used method even in households- using a

refrigerator. The refrigerator maintains a low temperature such that it

slows down the growth of microbes and keeps food fresh for longer.

Freezing is another low-temperature method used to preserve food

where the temperature is maintained at -18 degrees Celsius.

4. Using chemicals or preservatives

These are substances that are added to foods to prevent or slow down

their spoilage. The preservatives that are added, need to fulfill certain

criteria before they are deemed fit to be added to foods. Few

properties of preservatives are – they should be able to inhibit a wide

range of microbes, should be safe for human consumption, should not

affect the taste, flavor, color or properties of the food being preserved,

should not activate any other change in the food being preserved.

Commonly used preservatives are sulfites, sorbic acids, sodium

nitrate, and benzoic acid.

5. Acids

Citric acid and Acetic acid are commonly organic acids that are used

to preserve food substances such as pickles, sauces chutneys, and

vegetables. Being acidic, they inhibit the growth of the

micro-organisms and thus are effective food preservatives.

(Source: Wikipedia)

6. Drying

Many foods such as chips, papad, vegetables like methi or ginger are

dried or dehydrated and preserved. By dehydrating, the moisture

inside these substances is removed and thus micro-organisms are

unable to thrive on them, thus, preserving them.

7. Radiation

This method of preservation is used commonly for increasing the shelf

life of meat, seafood and poultry. Irradiating these food substances

helps to kill any pathogens and microbes that are present in them and

prevent the growth of others.

Humans have always tried and preserved their food items and other

perishable items. The methods have either changed or evolved, but the

purpose remains the same.

Look around and observe how many of these methods you have seen

at home or around you.

Solved Example for You

Q: Fruits kept in the refrigerator maintain their flavour and taste for

longer period due to

a. Non-availability of CO2

b. Presence of excess O2

c. Delay in the process of respiration

d. Presence of excess moisture

Solution: The correct answer is option “c”. Freezing is one of the

oldest and most widely used methods of food preservation. Very low

temperatures mean microorganisms cannot grow due to their delayed

metabolic activities like respiration.

Microorganisms and its Uses

The term ‘microorganisms’ include bacteria, fungi, viruses and

protozoa. We almost always presume they are harmful to us. So this

is because we read about how they cause diseases to both plants and

animals including humans. But, it is a fact that microorganisms are

useful to us in many ways. Microorganisms help in the production of

many food items, making medicines, keeping the environment clean,

in manufacturing and in research. Let us learn about microorganisms

and its uses.

(Source: Gallinee) 

Microorganisms and its uses

1. Production of dairy products:

Bacteria are the key players here. Bacteria help in fermentation which

helps in making different forms of dairy products from milk like curd,

buttermilk, butter, cheese. Streptococcus is the most common genus of

bacteria that are used in the commercial production of this product.

Learn more about Disease-Causing Microorganisms here in detail.

2. Bread Baking:

A species of Streptococcus is added to the dough before making bread

to bring about the required fermentation.

3. Alcoholic Drinks:

Alcoholic drinks are prepared or manufactured by the process of

fermentation. Each drink is derived from a different starting product

such as potato and grapes. Then it is fermented, distilled and alcohol is

prepared. The commonly used microorganism here is different types

of fungus like yeast. Some even use bacteria and fungus. Alcoholic

drinks include wine, rum, vodka etc.

4. Organic acids:

Organic acids are commercially prepared using fungi. Acetobacter,

Rhizopus, Penicillium are a few fungi that are used to ferment

substrates such as fruits and sugar-containing syrups. Examples of

acids that are derived and manufactured on a large scale using fungi

are acetic acid, citric acid, gluconic acid, fumaric acid and lactic acid.

5. Enzymes:

Many microbes are used in the derivation of enzymes such as lipase,

lactase, protease, peptidase to name a few.

6. Steroid production:

Some bacterial and fungal species are used in the preparation of

steroids that are then injected into the human body for different

purposes.

7. Help in sewage treatment:

Not only are microorganisms helpful to our body, they are also helpful

to the environment. They help in the secondary treatment stage of

sewage treatment.

8. Used as insecticides:

Certain bacterial and fungal species are used to keep certain insects

and pests away from crops.

9. Fertility of soil:

Microorganisms play a very important role in maintaining the fertility

of the soil. They help in the composting process which forms manure.

Also, microorganisms present in the soil help aerate it and enrich the

soil with nitrates and other nutrients. These nutrients are needed by the

crops for an abundant harvest.

Learn how Nitrates are converted to Nitrogen here.

(Source: Noble Research Institute)

10. Production of vitamins:

An essential vitamin that people need for proper digestion is Vitamin

B 12. Fungi are responsible for manufacturing B12.

11. Production of antibiotics and antivirals:

Bacteria and viruses are isolated and their antigens and enzymes are

extracted. These antigens help in the development of antibiotics and

antivirals.

12. Biotechnology and research:

So many labs use bacteria, fungi and especially viruses for research

studies. Non- virulent forms of these microorganisms are injected into

subjects going through clinical trials. This in future helps in the

development of medicines, vaccinations and cure for diseases. And

DNA and RNA studies also make use of them.

It is important for us to know about microorganisms and its uses as

they are both beneficial as well as harmful to other life forms. They

play a crucial role in the ecosystem. Maintaining a balance between

the ‘good’ and ‘bad’ microorganisms is the key to coexisting with

them.

Solved Example for You

Q: From which of the following Antibodies are obtained?

a. Bacteria

b. Viruses

c. Angiosperms

d. Gymnosperms

Solution: The correct answer is option “a”. Antibodies are chemicals

that kill or inhibit the growth of bacteria. They are used to treat

bacterial infections.

Nitrogen Cycle

We are generally under the impression that we only need oxygen to

live. Well, you couldn’t be more wrong! There is a laundry list of

elements that animals need for survival. One such element is Nitrogen.

But we can’t just get nitrogen from the air. It needs to be converted to

nitrates, via a process called nitrogen cycle. So let us learn more about

this fascinating concept.

The air we breathe contains 78% nitrogen, 21% oxygen and remaining

are other trace gases. The nitrogen component of air is inert. So this

means plants and animals cannot use it directly. To be able to use

nitrogen, plants convert atmospheric nitrogen to nitrates, nitrites and

ammonia compounds by a process called the nitrogen cycle. Animals

derive their nitrogen requirements from plants. 

What are the steps involved in the nitrogen cycle?

Nitrogen cycle consists of four main steps namely:

1. Nitrogen Fixation

2. Ammonification/ Decay

3. Nitrification

4. De-nitrification

It is important to note that microorganisms play an important role in

each of these steps.

What is the mechanism of each of these steps?

Nitrogen Fixation

This is the first step of the nitrogen cycle. This step is characterized by

the conversion of atmospheric N2 into ammonia (NH3). Bacteria like

Azotobacter and Rhizobium have a major role in this process. They

are harbored in the roots of the leguminous plants and help convert

inert nitrogen to ammonia. Nitrogen fixation can occur in any of the

following ways: atmospheric fixation (involves lightening), industrial

fixation(manufacturing ammonia under high temperature and pressure

condition)

Assimilation

Once the nitrogen has been fixed in the soil, plants can absorb

nitrogen through their roots. This process of absorption is known as

assimilation.

Ammonification

This is another process by which ammonia can be generated. Organic

remains of plants and animals are broken down in the soil by some

bacteria to release ammonia into the soil. These dead and waste matter

is used by these microorganisms as food and they release ammonia

into the soil.

Nitrification

This occurs in two-steps. The first step is in which NH3/NH$+ is

converted to NO3- (nitrates). The bacteria Nitrosomonas and

Nitrococcus present in the soil convert NH3 to NO2-, and another

bacterium, Nitrobacter converts NO2- to NO3-. These bacteria gain

energy through these conversions.

Denitrification

Is the reverse of nitrification that occurs in the deep layers of soil

where the bacteria convert NO3- is converted into N2 and other

gaseous compounds like NO2. This occurs because in deep layers of

soil, oxygen is not available and the soil bacteria use these nitrogen

compounds instead of oxygen.

What are some Essential Mineral Elements?

What is the importance of the nitrogen cycle?

● As we all know by now, the nitrogen cycle helps bring in the

inert nitrogen from the air into the biochemical process in

plants and then to animals.

● Plants need nitrogen to synthesize chlorophyll and so the

nitrogen cycle is absolutely essential for them.

● During the process of ammonification, the bacteria help

degrade decomposing animal and plant matter. This helps in

naturally cleaning up the environment.

● Due to the nitrogen cycle, nitrates and nitrites are released into

the soil which helps in enriching the soil with nutrients needed

for cultivation.

● As plants use nitrogen for their biochemical processes, animals

obtain the nitrogen and nitrogen compounds from plants.

Nitrogen is needed as is an integral part of the cell composition.

It is due to the nitrogen cycle that animals are also able to

utilize the nitrogen present in the air.

Solved Example for You

Q: Nitrates are converted into Nitrogen by

a. Ammonifying Bacteria

b. Denitrifying bacteria

c. Nitrogen-fixing bacteria

d. All of the above

Solution: The correct answer is “b”. Denitrification is the process

where after nutrients are converted back into ammonia, anaerobic

bacteria will convert them back into nitrogen gas.

Heterotroph – Definition, Functions, Types

Heterotrophs refer to an organism that consumes other organisms

available in the food chain. Furthermore, this organism is unable to

create organic substances from inorganic substances. Students can

learn more information about heterotroph here.

Definition and Meaning of Heterotroph

A heterotroph refers to an organism that produces its own food.

Furthermore, such an organism relies on gaining nutrition from other

sources of organic carbon. Moreover, these sources are mostly plant or

animal matter.

Heterotrophs in the food chain are primary, secondary, and tertiary

consumers, but certainly not producers. Moreover, heterotrophs

among the living organisms include all the animals and fungi,

bacteria, and parasitic plants.

Types of Heterotrophs

The various types of heterotrophs are as follows:

● Organotrophs

● Lithotrophs

● Chemotrophs

● Phototrophs

● Photoorganoheterotrophs

● Chemolithoheterotrophs

● Mixotroph

Organotrophs – These heterotrophs indulge in exploiting the carbon

compounds as the electron sources, like fats, proteins, and

carbohydrates from animals and plants.

Lithotrophs – These heterotrophs indulge in the usage of inorganic

compounds. Furthermore, these inorganic compounds are ammonium,

sulfur, and nitrite so as to obtain electron sources.

Chemotrophs – These organisms use the energy which is obtained by

the process of oxidation of chemicals. Furthermore, this energy is

obtained from the environment.

Phototrophs – This refers to heterotrophs that undertake utilization of

light to gain energy and carry out the processes of metabolism.

Photoorganoheterotrophs – These organisms certainly synthesize the

organic compounds by making use of sunlight along with the

oxidation of organic substances, which include elemental sulfur,

thiosulfate, hydrogen sulfide, and molecular hydrogen.

Most noteworthy, some examples of such organisms include

rhodospirillaceae and purple non-sulfur bacteria. Moreover, such

organism uses organic compounds to build the structures.

Furthermore, they do not fix carbon dioxide and do not have the

Calvin cycle.

Chemolithoheterotrophs – These organisms obtain their energy from

the oxidation of the inorganic compounds. A popular example of

Chemolithoheterotrophs is the Oceanithermus profundus.

Mixotroph – This is an organism that uses either organic carbon or

carbon dioxide as carbon dioxide. Moreover, what this means is that

mixotrophs have the ability to use the methods of both autotrophs and

heterotrophs. Consequently, they can grow under both heterotrophic

as well as autotrophic conditions.

Functions of Heterotrophs

There are many heterotrophs that use organic carbon as their source of

carbon. Furthermore, the organic chemicals as their energy and source

for electron.

Heterotrophs certainly function as consumers in the food chain.

Moreover, they get nutrients from parasitic, saprotrophic as well as

holozoic nutrients. Also, they indulge in breaking down complex

organic compounds. Release of energy results by oxidizing carbon and

hydrogen atoms that are available in carbohydrates, lipids, and

proteins.

Heterotrophs catabolize organic compounds by respiration,

fermentation, or both. Fermenting heterotrophs can be facultative or

obligate anaerobes. Furthermore, fermenting heterotrophs carry out

fermentation in environments of low oxygen.

Respiration in heterotrophs is almost always accompanied by

mineralization. Mineralization refers to the process of converting

organic compounds into the forms of inorganic nature. Furthermore,

when the organic nutrient used by the heterotroph contains very

important elements. Moreover, these elements are N, S, P, C, H, and

O.

Htereotrophs allow for dephosphorylation as something which is a

part of decomposition. The conversion of N and S from their organic

form to the inorganic is a vital part of the sulfur and nitrogen cycle.

H2S results from desulfurization which is ultimately oxidized by

lithotrophs and phototrophs.

Solved Question on Heterotrophs

Q1 Which of the following statements is not true in the case

heterotroph?

A. Heterotrophs in the food chain are never primary, secondary, and

tertiary consumers

B. It refers to an organism that produces its own food

C. It refers to an organism which consumes other organisms

D. It refers to an organism which relies on gaining nutrition from other

sources of organic carbon

A1 The correct option is A., which is “heterotrophs in the food chain

are never primary, secondary, and tertiary consumers. This is because,

“heterotrophs in the food chain are certainly always primary,

secondary, and also tertiary consumers.”

Inoculation – Definition and Types of Media Used for Inoculation

Microbiology is a branch of science that deals and focuses on

microorganisms. Microbiology deals with the study of bacteria,

unicellular organisms and viruses. We learn many new terms while

studying microbiology such as inoculation. Inoculation meaning in

microbiology is that transfer from culture for their growth. It is the

direct transfer from the culture of microorganisms to inoculation

needle.

Meaning of Inoculate in Microbiology

In microbiology, the definition of inoculation is different from

common terms such as health, vaccines, and immunology. Inoculation

is the study of introducing microorganisms into environments where

they will grow and reproduce. In other words, we can say that

inoculation means introducing a certain substance into another

substance.

For example, inoculation is adding a certain type of nutrient or

chemical into a suspension of bacteria. We can say that inoculating a

suspension with a particular nutrient or chemical.

This definition is in use in laboratory and researches in which

scientists study the growth of microorganisms in a specific

environment, study certain species and strains of microorganisms.

There is a similarity in the definition of inoculation in microbiology

and in immunology.

For example, a vaccine is a method of injection of pathogens into a

person’s body where they grow and from our immune system. Thus,

in this way, vaccines are able to protect us from pathogens that harm

our body they weaken the foreign pathogens before they grow in our

body.

Types of Media Used for Inoculation

● Agar Plates

● Broth Culture

● Slant culture

● Plate culture

● Stab culture

Agar Plates

Agar plates are some of the most common media which are in use for

growing bacteria and other microorganisms. A mixture of agar and

nutrients necessary for bacterial growth. This is then poured into

circular Petri dishes where the agar solution solidifies. After this,

inoculation of a solution-containing microorganism onto these plates

with the help of streaking.

A small streaking loop is a dip into a solution, which contains

bacterial cells that are used to streak onto the plates with the bacteria.

These plates are stored at the proper temperature for bacterial growth

for further study. We can also inoculate liquid media suspensions of

bacteria to grow and reproduce.

A single culture of microorganism added to a small solution to form a

mixture and pipette into liquid media. For Bacterial growth, we need

media in which the mixture of microorganism and solution contain

nutrients, compounds, and other necessary molecules.

Broth Culture

An inoculation needle used in inoculating a sterile broth culture.

Flaming the open end of the broth will keep it sterile. The broth

moved up to the needle so that the tip of the needle is submerged

while maintaining the original position of the needle.

Swirling of the needle carefully can help the inoculation of the

microorganism from the needle to the sterile broth. The inoculated

broth culture then removed from the needle. With the help of the

Aseptic technique which is applied to the open end of the broth culture

so as to prevent contaminants, and the needle is flamed for

sterilization.

Slant Culture

To inoculate a slant culture in a fishtail inoculation technique we use

inoculation needle. After transferring the microorganisms from the

original microbial culture to the inoculation needle the sterile slant

culture is uncapped. The open end of the uncapped slant culture is

then flamed.

The position of the slant is such that it moves the needle up until the

tip of the inoculation needle comes in contact with the base surface of

the sterile media. A zigzag pattern is formed on the agar surface when

the inoculation needle inoculates the sterilize agar by the manipulation

of the media. To remove the inoculation needle, we use an aseptic

technique.

Plate Culture

Inoculation of a plate culture uses a streaking technique to make a

streak plate. The inoculation needle streaked across the plate in

controlled directions, after lifting the lid so that it hovers above the

sterile agar plate. Microbial aerosols created from the hitting of the

inoculation tip to the sides of the agar plate. The inoculation needle

removed from the inoculated agar plate culture and flamed.

Stab Culture

In inoculating a stab culture, an inoculation needle is an essential tool.

Removal of a sterile stab culture cap is completed and the open end of

the needle is flamed. The needle tip and length of the needle is pushed

into the stab media until the needle reaches 0.5 inches away from the

bottom of the stab media. The inoculation needle is removed from the

media in the same direction and path that it was pushed into the stab

media to prevent the wobbling effect that may disturb the culture. We

can sterilize the needle with the help of a flame.

Solved Questions on Inoculate in Microbiology

Q. What do you mean by Inoculation Needle?

Ans: An inoculation needle is laboratory equipment that is useful in

the field of microbiology to transfer and inoculate living

microorganisms. It is one of the most common tools in a biological

laboratory. It is of two types disposable or re-usable. A reusable

inoculation needle made up of nichrome or platinum wire attached to a

metallic handle whereas disposable inoculation needle made up of

plastic resin.