Microbiology is the study of small living things. Generally, this means living things that are too small to see without the use of a microscope. These life forms are called microorganisms or microbes. Microorganisms include bacteria, archaea (a type of prokaryote a bit like bacteria but they have a distinct evolutionary origin), viruses, protozoa (single-cell eukaryotes like amoeba), microscopic fungi and yeasts, and microscopic algae (plant-like organisms). Microorganisms were discovered over three hundred years ago and it is thought that many new microbes have yet to be discovered. Microbiology is a wide area of science that includes bacteriology, virology, mycology, phycology, parasitology, and other branches of biology.

Most living things can be classified into prokaryotes or eukaryotes depending on whether their nuclear material (for example DNA) is surrounded by a membrane or not. Archaea and bacteria are prokaryotes. Most animals (including humans) and plants are eukaryotes. Protozoa, fungi, yeasts, and algae are eukaryotes. Viruses are a little different. Traditional classification systems do not classify viruses as living organisms. However, in practise they are considered microorganisms. The study of viruses is called virology.

Microbiology therefore includes the study of both prokaryotic and eukaryotic microorganisms. In practise the majority of microbiology is concerned with bacteria and/or viruses although eukaryotic microbiology is also a very important branch of microbiology. Many diseases of animals (including humans) and plants are caused by bacteria, viruses, amoeba, and fungi. Bacteria are important in probiotics, they are used in food production (e.g. yoghurt and cheese) and biotechnology. Yeasts and fungi are important in food and drink production (e.g. wine, beer, bread) and are also used to produce important pharmaceuticals (e.g. antibiotics).

DISINFECTION

Disinfection is the process, which involves the elimination of most pathogenic microorganisms (excluding bacterial spores) on inanimate objects. •Chemicals used in disinfection are called disinfectants. Different disinfectants have different target ranges, not all disinfectants can kill all microorganisms.

Importance of disinfection

The method of disinfection is used internationally for the safety of humans, to decrease the scale of transmission of diseases. A large emphasis of sterilisation and disinfection has been placed in the food industry, water sanitisation and medical care and hospitals. These sectors have been found to be largely affected with microorganisms in varying modes of transmission amongst the population. Different disinfectants are used in different industries, which target the specific flora.

Disinfection techniques are classified according to

Consistency

• Liquid (Alcohols, Phenols)

• Gaseous (Formaldehyde vapor, Ethylene oxide)

Spectrum of activity

• High level

• Intermediate level

• Low level

Mechanism of action

• Action on membrane (Alcohol, detergent)

• Denaturation of cellular proteins (Alcohol, Phenol)

• Oxidation of essential sulfhydryl groups of enzymes (H₂ O₂, Halogens)

• Alkylation of amino-, carboxyl- and hydroxyl group (Ethylene Oxide, Formaldehyde)

• Damage to nucleic acids (Ethylene Oxide, Formaldehyde)

Chemical disinfectants

• Alcohol
  • Chlorine and chlorine compounds
  • Formaldehyde
  • Glutaraldehyde
  • Hydrogen peroxide
  • Iodophors
  • Ortho-phthalaldehyde (OPA)
  • Peracetic acid
  • Peracetic acid and hydrogen peroxide
  • Phenolics
  • Quaternary ammonium compounds

Common uses of disinfectants:

Aldehydes: surface disinfection, fumigation of rooms, chambers and operating theatres.

Alcohol: 70% aqueous alcohol is more effective at microbial killing. 70% Ethyl alcohol is used as antiseptic on skin.

Phenol: Is used in high concentrations as a disinfectant and in low concentrations as an antiseptic.

Halogens: Iodine (antiseptic), Chlorine (bleach)

STERILIZATION

Sterilization is a process in which all the living microorganisms, including bacterial spores are killed. It can be achieved by physical and chemical methods.

Sterilization is employed to minimize the growth of organisms and transmission of disease from one individual to another. In the environment the use of disinfection techniques decreases the growth of bacteria on surfaces, which leads to the decrease in transmission of organisms amongst the population. These techniques are commonly used today in medical care and food industry.

Physical methods

• Heat (Dry and moist)

• Sunlight

• Vibration

• Radiation

• Filtration

Heat is considered to be most reliable method of sterilization of objects that can withstand heat. Heat as Moist and Dry heat are the most common sterilizing methods used in hospitals and are indicated for most materials.

Dry Heat: Causes denaturation of proteins and oxidative damage.

Techniques include:

• Red Heat (common uses: straight wires, bacterial loops and spatulas)

• Flaming (Common uses: bacterial loops, wires and spatula’s)

• Incernation (common uses: soil dressing, pathological bedding)

• Hot Air oven (discovered by Louis Pasteur, common uses: in dairy industry)

• Infra red rays (common uses: heat glassware and metallic instruments)

Moist Heat: 


Moist heat is more efficient in contrast to dry heat; it causes coagulation and denaturation of proteins. 


At temperature below 100°C:

• Pasteurisation: Food (dairy) Industry

• Vaccine bath: (vaccine sterilisation)

• Serum bath: (serum contaminants, does not kill spores survive)

• Inspissation: (egg and serum containing media, can kill spores)


At temperature 100°C:

• Boiling: Boiling water (100°C)

• Steam (100°C)

At temperature above 100°C:

• Autoclave: works at 121^oC at 15 psi

Radiation

There are 2 types of Radiation:

Non-ionizing: wavelength longer then visible light.

• UV Radiation has a wavelength of 200-280nm; it has a germicidal effect on microorganisms.

• Common uses: Surface disinfection, in hospitals, operating theatre and laboratories.

Ionising: 2 types:

• Particulate (Electron beam)

• Common uses: sterilization of instruments such as syringes, gloves, dressing packs, foods and pharmaceuticals.

• Electromagnetic (Gamma rays)

• Common uses: sterilization of disposable Petri dishes, plastic syringes, antibiotics, vitamins, hormones and fabrics.

FIELDS AND SCOPE OF MICROBIOLOGY

Microbiology has two major fields

1. Pure Microbiology
2. Applied Microbiology

Pure Microbiology: on the basis of Taxonimical classification

• Bacteriology
• Mycology
• Virology
• Protozoology
• Immunology

On the basis of integrative characteristics

• Microbial cytology
• Microbial physiology
• Microbial genetics
• Microbial ecology
• Microbial taxonomy
• Cellular Microbiology
• Molecular Microbiology

2. Applied Microbiology: on the basis of application

• Medical Microbiology
• Veterinary Microbiology
• Public Health Microbiology
• Industrial Microbiology
• Pharmaceutical Microbiology
• Agriculture Microbiology
• Plant Microbiology
• Soil Microbiology
• Food and Dairy Microbiology
• Environmental Microbiology