Microbiology

Microbiology Study Guide

infectious agent that can replicate only inside the living cells of other organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea. Since Dmitri Ivanovsky's 1892 article describing a non-bacterial pathogen infecting tobacco plants, and the discovery of the tobacco mosaic virus by Martinus Beijerinck in 1898, about 5000 viruses have been described in detail, although there are millions of different types. Viruses are found in almost every ecosystem on Earth and are the most abundant type of biological entity. The study of viruses is known as virology , a sub- specialty of microbiology. 1.3 Microbial Laboratory Techniques Microscopy Microscopy is the use of microscopes to view samples and objects that cannot be seen with the unaided eye. The three branches of microscopy are optical, electron, and scanning probe. Optical and electron microscopy involve the diffraction, reflection, or refraction of electromagnetic radiation/electron beams interacting with the specimen, and the subsequent collection of this scattered radiation or another signal in order to create an image. Scanning probe microscopy involves the interaction of a scanning probe with the surface of the object of interest. Stain Procedures Because microbial cytoplasm is usually transparent, it is necessary to stain microorganisms before they can be viewed with the light microscope. In some cases, staining is unnecessary, such as when microorganisms are very large or when motility is to be studied. A drop of the microorganisms can be placed directly on the slide and observed. A preparation such as this is called a wet mount. A wet mount can also be prepared by placing a drop of culture on a cover-slip (a glass cover for a slide) and then inverting it over a hollowed-out slide. This procedure is called the hanging drop. In preparation for staining, a small sample of microorganisms is placed on a slide and permitted to air dry. The smear is heat fixed by quickly passing it over a flame. Heat fixing kills the organisms, makes them adhere to the slide, and permits them to accept the stain. Media Preparation and Growth Microorganisms need nutrients, a source of energy, and certain environmental conditions in order to grow and reproduce. In the environment, microbes have adapted to the habitats most suitable for their needs, in the laboratory, however, these requirements must be met by a culture medium. This is basically an aqueous solution to which all the necessary nutrients have been added. Depending on the type and combination of nutrients, different categories of media can be made.

©2018

Achieve

Page 11

of 132