LAB 1: PRINCIPLES AND USE OF MICROSCOPE

1.1 Setting up and using the microscope

Introduction

In order to be seen, microorganisms need to be magnified. Despite advances in other area of microscopy (for example, the electron microscope), the light microscope is still the instrument most frequently used for viewing microorganisms. The science of investigating small objects using such an instrument is called microscopy.

The part of microscope.

The following description is generalized to cover a typical microscope (see figure below)

The light source bulb is located in the base of the microscope. It projects light upwards through the diaphragm, the specimen and the lenses in order for the specimen to be seen. The on–off switch turns on the current to the bulb while the voltage control dial control the brightness of the bulb.

          
The diaphragm has different sized holes and is used to vary the intensity and size of the cone of light that is projected upward into the slide. It acts like the iris of our eyes. There is no set rule regarding which setting to use for a perticular power. Rather, the setting is a function of the transparency of the specimen, the degree of contrast you desire and the particular objective lens in use.

The stage is the platform where you place your slide. Stage clips hold the slides in place. If your microscope has a mechanical stage, you will be able to move the slide around by turning two knobs. One moves its left and right, the other moves up and down.

The fine-focus adjustment knob and coarse-focus adjustment knob are used to move the stage either upwards or downwards. The only difference between them is the fine-focus adjustment knob moves the stage slightly while the coarsefocus adjustment knob moves the stage rapidly. Thus, the coarse-focus adjustment knob should not be used while you are examining a specimen.

The light microscope has a 4 objective lenses which are located on the revolving nosepiece. They consist of 4x, 10x, 40x, and 100x powers. When coupled with a 10x eyepiece lens, you will get a total magnifications. The shortest lens is the lowest power, the longest one is the lens with the greatest power. It focuses the light passing through the specimen to form a magnified primary image.

            
The body tube or the eyepiece tube is used to connect the eyepiece to the objective lenses. It also receives the light coming through the objective and redirects it to the eyepiece.                    

      
The ocular lens or also known as the eyepiece are the lens at the top that you look through. They are usually 10x or 15x power. It consist of several lenses that collects the light from the eyepiece tube, focus it and transmit light to your eyes so that the specimen can be seen.    

Magnification and resolution.
The total magnification of the specimen or sample observed are calculated by multiplying the objective lens multiplication power and the eyepiece lens multiplication power. The calculations are as shown below:

4x objective X 10x eyepiece = 40x magnification

10x objective X 10x eyepiece = 100x magnification

40x objective X 10x eyepiece = 400x magnification

100x objective X 10x eyepiece = 1000x magnification

The minimum distance between two points which is visible through a microscope (lenses) is termed as resolution of a microscope. The ability of a microscope to distinguish between two separate objects is called the resolving power of the microscope. Sometimes, blurred images may be seen through the lenses. This is because of the placing of two distinct points too close to each other, which results in overlapping of the images. Magnification can neither improve nor decrease the resolving power of the microscope.

Result 

1. Escherichie coli

10x objective X 10x eyepiece

colour : light pink

rod-shaped

This virulent strains of E.coli can cause urinary tract infections. 

 2. Stophyloccus aureus

10x objective X 40x eyepiece

colour: dark green

shape: grape-liked cluster ( small rounds )

a gram-positive bacteria 

Staphylococcal toxins are a common cause of food poisoning as they can be produced in improperly-stored food.

Clostridium perfringes

10x objective X 40x eyepiece

rod-shaped

third-most-common cause of food-borne illness

 Discussion.

Staphylococcus aureus is facultative anaerobic and gram-positive cocci which occur singly in pairs and irregulular clusters. Under microscope that we observed with 10x40 magnifications the colour of staphylococcus aureus is dark green. Staphylococcus aureus is non-motile, non-spare forming,catalase and coagulase positive. S.aureus is catalase positive can produce enzyme catalase. It is able to convert hydrogen peroxide to water and hydrogen. Also it makes the catalase test useful to distinguish staphylococci for entrococci and streptococci. S.aureus strains many appear in dirty white and nonhemolytic.

Escherichia coli are a gram negative, faculatative anaerobic and non-spore forming. Cells of E.coli typically rod-shaped with 1 to 2µm wide and 3 to 30µm long. E.coli uses mixed- acid fermentation in anaerobic conditions, produce lactase, succinate, ethanol, acetate and carbon dioxide. Optimal growth of e.coli occurs at 37ºC with temperature of up 49 ºC (120ºF). 

Clostridium perfringes are spore forming of the genus clostridium and gram positive bacillus. Clostridium perfringes same with E.coli shape, that is rod-shaped and anaerobic. On blood agar plates, C.perfringes grown anaerobically produces flat, spreding, rough, translucent colonies with irregular margins.

Conclusion

From the experiment, we can conclude that 10x objective X 10x eyepiece=100x magnification can show a very clear image of culture studied. The bright field microscope also show a very clear colored image.

References.

http://en.wikipedia.org/wiki/Clostridium_perfringens

http://en.wikipedia.org/wiki/Staphylococcus_aureus

http://en.wikipedia.org/wiki/Escherichia_coli