Culture and Culture Media

Pure culture: A culture that contains only one kind of microorganism is called a pure culture. A culture which contains more than one kind of microorganism is called a mixed culture. A pure culture has only a single type of colony. Pure cultures are essential in order to study colony characteristics, biochemical properties, morphology, staining reaction, immunological reaction or susceptibility towards antimicrobial agents of particular strain of fungus, bacteria or actinomyces. Read more

Microscopy and Types of Microscopes

Microscope is an optical instrument consisting of lens for making enlarged or magnified images of minute objects. Robert Hook (1635 – 1703) made and used a first compound microscope. The basic difference between simple and compound microscope is that simple microscope uses only one lens whereas, compound microscope uses more than one lenses to further magnify the object.

Fig: compound microscope

The ability of microscope to distinguish two adjacent object as separate and distinct images rather than single blurred image is called resolving power of microscope. Theoretically, size of image can be increased by adding lenses. Magnification of object is only useful if the enlarged image is clearly visible. So, effective magnification depends on resolving power of microscope.

A microscope’s resolving power is dependent on wavelength of beam for illumination and optical quality of lenses. Shorter wavelength gives better resolution. Resolution or shortest distance (d) can be calculated by using the formula, d = λ/2nsinϴ  where, d = resolution, λ = wavelength of light, n = refractive index and ϴ = angle subtended.

Note: Oil is used with oil immersion lenses because it has higher numerical aperture than air and also higher refractive index and this greatly improves resolution. Read more

General Laboratory equipment

Fig: Autoclave

Autoclave: Autoclave is a sealed devise that allows the entrance of steam under pressure. The use of moist heat facilitates killing of all microorganisms including heat resistance endospores. The underlying principle is, with increase in steam pressure, the temperature also rises. The water boils at 100°C upon the vapor pressure of atmosphere. Temperature will increase if vapor pressure is increased. The autoclave is operated at 15lb/inch2 for 30 minutes. This temperature for a period of 30 minutes is sufficient to kill all the vegetative and spore cells of microorganism. Pressure temperature relationship is given as Read more

Introduction and Scope of Microbiology

Microbiology is the study of microorganism; a large diverse group of microscopic organism that exist as a single cell or cell clusters. It also includes virus which are microscopic but not cellular. Microbial cells are thus distinct from cells of animals and plants which are unable to live alone in nature and exist as only part of multicellular organism. A single microbial cell is generally able to carry out its life process of growth, energy generation and reproduction independently of other cells, either of same kind.

The existence of microbes was not established until Antony Von Leeuwenhoek (1678) could see them in simple microscope. Lewis Pasteur (1822 – 1895) investigated that boiled medium could remain clear in swan necked flask. Pasteur developed the procedure of gentle heating (pasteurization) to prevent the spoilage of beer and wine by undesirable microbes. This process was later used to prevent milk borne diseases in human beings. Read more