Stain and Staining Procedures

Stain and staining procedures


Micro-organism can be identified by microscopic examination.These micro-organisms are very small, transparent, and invisible to our naked eyes so it is very difficult to observe these micro-organisms.

These microbial cells are colourless so when these cells are suspended in the aqueous medium the refractive index of the cell and aqueous medium is very low and same and due to lack of contrast observation of such unstained organism is very difficult. So staining of micro-organism in microbiology is an essential step for bacteriological studies.

Purpose of staining

  • Staining procedure helps in the production of contrast between micro-organism an aqueous medium.
  • It is useful to study morphological of bacteria.
  • Staining helps in studying internal as well as external characters of bacteria.


1. Dye – Dye is an organic compound made up of auxochrome and chromophore group these groups are linked to a benzene ring. Dye is used for colouring non-biological objects.

Read moreStain and Staining Procedures

Corynebacterium Diphtheriae Disease

Corynebacterium Diphtheriae Disease

Corynebacterium diphtheriae is a causative agent of diphtheria.It is upper respiratory tract illness and it is a contageous disease.

1. Morphology

  • It is a Gram positive, non-motile, non spore forming bacteria.
  • Corynebacteria is non- capsulated slender rod.
  • It shows club shaped swelling and hence called as Corynebacteria.
  • Its size ranges from 3-6 μm in lenght and 0.6-0.8 μm in width.
  • These cells posses metachromatic granules.
  • Mode of multiplication is by binary fission.

2. Cultural characters

  • Corynebacterium can grow easily on ordinary media.
  • It growth is enhanced by addition of blood or serum in the media.
  • It grows in a temperature range of 15° C-40° C and optimum temperature for its growth is 36° C.
  • Neutral pH is optimum for its growth.
  • Corynebacteria diphtheriae may be aerobic or facultative anaerobic in nature.
  • They are fast growing organism.

Read moreCorynebacterium Diphtheriae Disease

Cell Wall of Gram Negative Bacteria

Cell wall of Gram negative bacteria

Cell wall of Gram negative bacteria is more rigid and thick then Gram postive bacteria.

It is made up of two layers

1. Peptidoglycan

2. Outer cell wall layer

Component of cell wall of Gram negative cell wall
Component of peptidoglycan of Gram negative cell wall

1. Peptidoglycan

  • It is present in between outer wall layer and cell membrane.
  • The structure is similar as gram positive cell wall.
  • There are some minor differences in the Gram positive and Gram negative peptidoglycan structure.
  • The differences are as follows:-
  1. The third amino acid of tetrapeptide side chainin Gram positive cell wall is L-lysin which is replaced by Mesodiaminopimilic acid in Gram negative cell wall.
  2. All N-acetymuramic acid molecules are not linked to tetrapeptide side chain.
  3. Cross bridges are not made up of glycin molecule they are made up of peptide bond.

Read moreCell Wall of Gram Negative Bacteria

Microbiology – Cell Wall of Gram Positive Bacteria.


  • A bacterial cell shows various parts and these parts have specific structure and functions.
  • These parts are separated by a rigid cell wall some parts are on the internal side of the cell wall and some parts are on the external side of the cell wall.
  • The parts present on the internal side of the cell wall are cell membrane, cytoplasm, nuclear region, reserve food material etc.
  • The cellular parts present on external to the cell wall are flagella, capsule and pilia.

Structure and function of Cell wall

  • The cell wall is the outer covering of bacterial cell in absence of capsule.
  • This cell wall is rigid in nature which imparts a proper shape to bacteria.
  • Cell wall encloses all internal parts of the cell.
  • On the basis of typical structure, composition and Gram staining they are classified

A)   Gram-positive bacteria.

B)   Gram-negative bacteria. Types of bacterial cell

Types of bacterial cell

Read moreMicrobiology – Cell Wall of Gram Positive Bacteria.

Microbiology – Morphology of Bacterial cell

Morphology means systematic study of external characters of bacteria.

Morphology of bacterial cell deals with study of

  1. Size of bacteria.
  2. Shape of bacteria.
  3. Arrangement of bacteria.

1. Size of bacteria.

  • Size of bacterial cell is less than 3 micrometer.
  • The bacteria are microscopic in nature and are visible only under compound microscope.
  • These bacteria may be spherical,cylindrical or spiral in shape.
  • Size of a spherical shape bacteria can be measures in diameter.
  • Size of a cylindrical bacteria is measured by its length and width.
  • In spiral shape bacteria length is measured but due to spiral form it is not exact.
  • As we know all bacteria are microscopic in nature so their size is also measured under microscope.
  • Size of bacteria is measured  by using calibrated slide and calibrated  occular compound microscope is used.
  • The above method of measuring size is called as micrometry.
  • The size of bacteria can also be measured by electron microscopic micrometry.
  • Units of measurement used in bacteriology are
  1. Micron or micrometer.
  2. Nanometer (nm) or Millimicron.
  3. Angstrom (A°)
  • The conversion are as follows
  • 1 μm = 10-3 mm = 10-4cm = 10-6 meter1 nm = 10-3 μm = 10-6 mm1 A0 = 10-1 nm = 10-4 m =10-7 mm
  • Size of spherical bacteria or cocci ranges from 0.5 to 3.0 μm.
  • Size of cylindrical or rod shape bacteria ranges from 0.15 μm to 2.0 μm in width and 0.5 μ to 20 μ in lenght.
  • The small size of bacteria have large surface area for entry of nutrients, water and exit of waste.

Read moreMicrobiology – Morphology of Bacterial cell

Microbiology – Characteristics of Eukaryotic cell

Microbiology – Characteristics of Eukaryotic cell

There are two types of cells on the basis of nucleus present within the cell.

  •  Prokaryotic cell. 
  •  Eukaryotic cell.

Eukaryotic cell 

Eukaryotic cell
Eukaryotic cell

Read moreMicrobiology – Characteristics of Eukaryotic cell

Characteristics of Prokaryotic Cells

Characteristics of Prokaryotic Cells

There are two types of cells on the basis of nucleus present within the cell.

1. Prokaryotic cell

2. Eukaryotic cell

1. Characteristics of Prokaryotic cell

Prokaryotic cell
   Prokaryotic cell

Read moreCharacteristics of Prokaryotic Cells

Infection and its Types in Microbiology

Infection and its Types in Microbiology


  • Infection is a condition of host in which parasite lives, multiplies in the host body.
  • Infection normally occurs when a parasite is very active and it suppresses the host defense mechanism.
  • Depending upon the nature of host, parasite and the persistence of the disease the infection is divided into following types.

1. Chronic infection

  • Chronic infection is a long lasting infection.
  • Examples :- Diabetes, Cancer, Sickle cell anemia, Autoimmune diseases etc .

2. Acute infection

  • It is a disease that spreads rapidly in short period of time.
  • Example:- Common cold, Chicken pox, Pneumonia etc.

Read moreInfection and its Types in Microbiology

Diseases and its Types in Microbiology

Diseases and its Types in Microbiology


  • The disease is an abnormal condition an uneasy state of the body.
  • The human body is constantly exposed to micro-organism sometime these micro-organisms are so active that they enter the host body, multiply and result in a disease.
  • Diseases are mainly of four types as shown below.


1. Epidemic

  • In an epidemic, an infectious disease spreads rapidly and a large population is affected 
  • The outbreak of disease is above the expected level.
  • Epidemic disease is of two types as shown below.

Read moreDiseases and its Types in Microbiology

Basics of Medical Microbiology

Basics of Medical Microbiology

Medical microbiology deals with studying the relationship between host and parasite and understanding the causative agent of disease.

In our daily life, human beings are constantly exposed to micro-organisms.
The interaction between human and micro-organisms may be useful or harmful interaction.
Parasitism can be explained a condition in which microbial population is benefited and the host is harmed.

Some important concepts in medical microbiology

1. Infection

  • In infection, a pathogen enters in a host body, lives and multiply in the host.
  • Generally, infection is caused due to the failure of host defence mechanism.
  • Due to the failure of host defence mechanism the microbial cells leads to infection.

2. Disease

  • The disease is a result of infection
  • When a disease is established the normal functioning of host body is disturbed and this disturbance results in signs and symptoms.
  • These pathogens not only multiply in the host but also releases some byproducts.
  • These byproducts may be toxic or non-toxic to host.

3.   Etiological agent

  • The etiological agent may be the causative agent of a disease
  • It may be an opportunistic pathogen

Read moreBasics of Medical Microbiology

%d bloggers like this: