lec assignment

7/28/2019 Lec Assignment

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Nestie Bryal C. Villaviray

MD 3y1-5

Brief history of microbiology:

Historians are unsure who made the first observations of microorganisms, but the microscope was available

during the mid 1600s, and an English scientist named Robert Hooke made key observations such as thestrands of fungi among the specimens of cells he viewed.

In the 1670s and the decades thereafter, a Dutch merchant named Anton van Leeuwenhoekmade carefulobservations of microscopic organisms, which he called animalcules. He is regarded as one of the first to

provide accurate descriptions of protozoa, fungi, and bacteria.

After van Leeuwenhoek died, the study of microbiology did not develop rapidly because microscopes were

rare and the interest in microorganisms was not high. In those years, scientists debated the theory ofspontaneous generation, which stated that microorganisms arise from lifeless matter such as beef broth. Thistheory was disputed by Francesco Redi, who showed that fly maggots do not arise from decaying meat (as

others believed) if the meat is covered to prevent the entry of flies.

Louis Pasteur worked in the middle and late 1800s. He performed numerous experiments to discover whywine and dairy products became sour, and he found that bacteria were to blame. Pasteur postulated the germ

theory of disease, which states that microorganisms are the causes of infectious disease.

Pasteur's attempts to prove the germ theory were unsuccessful. However, the German scientist Robert Kochprovided the proof by cultivating anthrax bacteria apart from any other type of organism.

A Golden Age of Microbiology emerged during which many agents of different infectious diseases were

identified. Many of the etiologic agents of microbial disease were discovered during that period, leading to

the ability to halt epidemics by interrupting the spread of microorganisms.

Then, after World War II, the antibiotics were introduced to medicine. In the 1940s, the electron

microscope was developed and perfected. With the development of vaccines in the 1950s and 1960s, suchviral diseases as polio, measles, mumps, and rubella came under control.

Nowadays, modern microbiology reaches into many fields of human endeavor, including the development

of pharmaceutical products, the use of qualitycontrol methods in food and dairy product production, the

control of disease causing microorganisms in consumable waters, and the industrial applications of

microorganisms.

Kochs Postulate

Pasteur's attempts to prove the germ theory were unsuccessful.

However, the German scientist Robert Koch provided the proof by

cultivating anthrax bacteria apart from any other type of organism.He then injected pure cultures of the bacilli into mice and showedthat the bacilli invariably caused anthrax. The procedures used by

Koch came to be known as Koch's postulates (Figure below). Theyprovided a set of principles whereby other microorganisms could

be related to other diseases.

The steps of Koch's postulates used to relate a specificmicroorganism to a specific disease. (a) Microorganismsare observed in a sick animal and (b) cultivated in the lab.


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(c) The organisms are injected into a healthy animal, and (d) the animal develops the disease.(e) The organisms are observed in the sick animal and (f) reisolated in the lab.

Bacterial Shapes

The most common shapes of bacteria include rod, cocci (round), and spiral forms. Cellular arrangementsoccur singularly, in chains, and in clusters. Some species have one to numerous projections called

flagella enabling the bacteria to swim, making them motile organisms.

1. Cocci (or coccus for a single cell) are round

cells, sometimes slightly flattened when they areadjacent to one another. Cocci bacteria can exist

singly, in pairs (as diplococci ), in groups of four (as

tetrads ), in chains (as streptococci ), in clusters (as

stapylococci ), or in cubes consisting of eight cells (as

sarcinae .)

2. Bacilli (or bacillus for a single cell) are rod-shaped bacteria. Since the length of a cell varies underthe influence of age or environmental conditions, you should

not use cell length as a method of classification for bacillus

bacteria. Like coccus bacteria, bacilli can occur singly, in pairs,or in chains. Examples of bacillus bacteria include coliform

bacteria which are used as an indicator of wastewater pollution

in water, as well as the bacteria responsible for typhoid fever.

3. Spirilla (or spirillum for a single cell) are curved bacteria which can

range from a gently curved shape to a corkscrew-like spiral. Many

spirilla are rigid and capable of movement. A special group of spirillaknown as spirochetes are long, slender, and flexible.


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Microscope:

A piece of laboratory equipment that is used to magnify small things that are too small to be seen

by the naked eye, or too small for the details to be seen by the naked eye, so that their finer details can

be seen and studied.

Commonly binocular (two eyepieces), thecompound light microscope,combines the power of lenses and light to enlarge the subject being viewed.Compound light microscopes are one of the most familiar of the different types

of microscopes as they are most often found in science and biology classrooms.

TheStereo microscope, also called a dissecting microscope, has two opticalpaths at slightly different angles allowing the image to be viewed three-dimensionally under the lenses. Used in watch making and

microsurgery.

The Digital Microscope, invented in Japan in 1986, uses the

power of the computer to view objects not visible to the naked eye.

TheUSB Computer microscope, among the different types of microscopes,can be used on almost any object and requires no preparation of the specimen.

TheElectron Microscope(EM) is a powerful microscope available and usedtoday, allowing researchers to view a specimen at nanometer size.

Parts and Functions:


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STRUCTURAL COMPONENTS

The three basic, structural components of a compound microscope are the head, base and arm.

Head/Body houses the optical parts in the upper part of the microscope Base of the microscope supports the microscope and houses the illuminator Arm connects to the base and supports the microscope head. It is also used to carry the microscope.

OPTICAL COMPONENTS

Eyepiece or Ocular is what you look through at the top of the microscope. Typically, standard eyepieceshave a magnifying power of 10x. Optional eyepieces of varying powers are available, typically from 5x-30x.

Eyepiece Tube holds the eyepieces in place above the objective lens. Binocular microscope heads typicallyincorporate a diopter adjustment ring that allows for the possible inconsistencies of our eyesight in one orboth eyes. The monocular (single eye usage) microscope does not need a diopter. Binocular microscopesalso swivel (Interpupillary Adjustment) to allow for different distances between the eyes of differentindividuals.

Objective Lenses are the primary optical lenses on a microscope. They range from 4x-100x and typically,include, three, four or five on lens on most microscopes. Objectives can be forward or rear-facing.

Nosepiece houses the objectives. The objectives are exposed and are mounted on a rotating turret so thatdifferent objectives can be conveniently selected. Standard objectives include 4x, 10x, 40x and 100xalthough different power objectives are available.

Coarse and Fine Focus knobs are used to focus the microscope. Increasingly, they are coaxial knobs -that is to say they are built on the same axis with the fine focus knob on the outside. Coaxial focus knobsare more convenient since the viewer does not have to grope for a different knob.

Stage is where the specimen to be viewed is placed. A mechanical stage is used when working at highermagnifications where delicate movements of the specimen slide are required.

Stage Clips are used when there is no mechanical stage. The viewer is required to move the slide manuallyto view different sections of the specimen. Aperture is the hole in the stage through which the base (transmitted) light reaches the stage. Illuminator is the light source for a microscope, typically located in the base of the microscope. Most light

microscopes use low voltage, halogen bulbs with continuous variable lighting control located within the base.

Condenser is used to collect and focus the light from the illuminator on to the specimen. It is located underthe stage often in conjunction with an iris diaphragm.

Iris Diaphragm controls the amount of light reaching the specimen. It is located above the condenser andbelow the stage. Most high quality microscopes include an Abbe condenser with an iris diaphragm.Combined, they control both the focus and quantity of light applied to the specimen.

Condenser Focus Knob moves the condenser up or down to control the lighting focus on the specimen.


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Nestie Bryal C. Villaviray

MD 3y1-5

lec assignment

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