Identification of different forms of bacteria.

TITLE: Identification of different forms of bacteria.

INTRODUCTION

Prokaryotic are unicellular cells which have many differences from eukaryotic cells. Prokaryotic cells do not have membrane bound organelles in them and have thread like DNA. Regardless of the differences they do have some similarities like membranes and cytoplasm (Talaro 1996). There are microorganisms which cannot be seen with the naked eye and can only be seen under the microscope. There are different kinds of prokaryotic cells like unicellular cells and bacteria (Prescott al 1993). Though, some protozoa have some characteristics of eukaryotic cells. Bacteria are single celled microorganisms that can exist either as independent organisms or as parasites (Prescott al 1993).

Cells are sometimes difficult to differentiate because some of the cells almost look like they are the same under the light microscope. Certain devices are used to differentiate these cells to their distinct characteristics. Almost all bacteria fall into two major structural groups that are distinguished by a technique called the Gram stain, devised in the 1800s by Hans Christian Gram a Danish bacteriologist. The gram stain is a good method of cell differentiation because the results are straight forward (Wolfe, 1993).

So the bacterial cells were first fixed using a flame, and after fixation the cells are usually stained with crystal violet and iodine and then exposed to a decolorizing organic solvent such as alcohol or acetone. The gram positive cells are resistant to decolourisation and retain a purple colour and the gram negative cells are less resistant so they rapidly decolorize and they retain a pink colour. The colour is retained inside gram positive cells and not in the wall, in some way the structure of the wall prevents decolourisation of the protoplasm in these cells (Talaro, 1996). Gram positive and gram negative cells differ in the way they respond to the dye used, the difference may be simply that gram positive walls are much thicker and retard the removal of stain more effectively than the very thin walls of the gram negative (Wolfe, 1993).

The bacteria are differentiated into two groups that are gram positive bacteria and gram negative bacteria. In gram positive bacteria such as Staphylococcus, Bacillus and lactobacillus have thick cell walls with thicker peptidoglycan layer in them. In gram negative bacteria such as Salmonella, E.coli and Azotobacter have thin cell walls and thin peptidoglycan layers (Monger, Roberts 2008). Another reason for their difference is that, gram positive walls consist of a single, relatively thick layer of apparently homogeneous polysaccharide wall material that is not visibly differentiated into sub layers. Gram negative cells also share unique molecular group called the peptidoglycans and teichoic acids as a wall constituent in gram positive, which serve as a recognition and binding sites (Wolfe, 1993).

AIMS

To identify the different forms of bacteria under the light microscope and comment on the size, shape, arrangement and color of the bacteria.

To culture bacteria and fungi in different nutrient plates, investigating the different forms of and diversity of bacteria and describe the growth.

OBJECTIVES

To view the various slides of bacteria provided under the microscope.
To comment on the shape, size, arrangement and color of bacterial cells.
To be able to identify different forms of bacteria.
To culture bacteria in nutrient agar and fungi in potato dextrose agar.
To be able to carry out the gram stain to investigate the different forms and diversity of bacteria.
To describe the growth of bacterial colonies on the surface of the agar.

MATERIALS AND METHODS

The laboratory was provided with the equipment which was used to carry out the practical experiment. The provide equipment were; light microscope, prepared slides of bacteria burner, alcohol, inoculating loops, nutrient agar plates and PDA. The first thing done was the aseptic technique to sterilize the working area and apparatus in order to prevent contamination. The first procedure of the practical was the culturing of the bacteria in nutrient agar plate. The bacterium was aseptically transferred from the broth onto the agar plate using the loop and was streaked on the plate surface. The plates were labeled and incubated for 24 hours at 37 degrees Celsius. The fungi hyphae were also transferred to the center of a fresh plate of PDA potato dextrose agar. The plates were labeled and incubated at 25 degrees Celsius for 24 hours. The second part was the viewing of prepared slides under the microscope and comment on the shape, size, arrangement and colour of the bacteria. The last stage was the gram stain procedure was used to stain the cultured bacteria and observe under the light microscope. The bacteria were heat fixed first before staining. Grams stain procedure as per practical schedule microbial forensics BSFS 205 practical 2.

RESULTS

Diagram 1; drawing of the spirilum as viewed under the light microscope

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Fig 1 gram negative bacteria

Bacteria Culture A

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Fig 2 gram positive bacteria

Bacteria Culture B

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DISCUSSION

Bacteria can grow on any environment as long as there are suitable conditions for it to grow. Bacteria can grow on either dry or moist conditions provided there is enough nutrients, food, correct temperature and pH (Talaro 1996). From the result section it shows that the practical experiment managed to help support that bacteria can grow when they are provided with the suitable conditions like the agar plates provided the nutrients. The bacteria in the agar plates retained from the incubator had grown and the colonies were like a lawn mesh. From the diagram there is a spirochete bacteria obtained from the prepared slide of spirilum. The bacteria spirillum was viewed as long and helical-shaped, also known as spirochetes. Their structure contributes to their ability to move in their corkscrew manner that they use to propel them along surfaces as they move. The flagellums on the ends of the spirillum provide the movement and speed to move the bacteria. Most of these spirillum bacteria do not form colonies and most of it was evident on the slides as they were usually singular along the plane of the slide (Breeze 2005). The other slide of rods and cocci could not be viewed due to technical problems with the microscopes and also that the slides are very old.

The results in figure 1 and 2 are the gram negative bacteria and gram positive bacteria respectively. The gram positive bacteria were from the bacteria culture B and the bacterial cells were very visible. The bacterial cells had a dense distribution. The bacterial cells were rod shaped and purple in colour. The purple colour is due to the double layer of peptidoglycan which retained the purple colour of the crystal violate in the cell membrane which shows their resistant to colour change. The gram negative bacteria in figure 1 were from culture A and the bacterial cells were pink in colour and viewed as rods with spores which looked as colourless or unstained areas.

REFFERENCES

Breeze, R. G, Budowle, B and Schutzer, S, E. Microbial Forensics (2005). Elsevier Academic Press Boston.
Monger, G and Roberts, M. 2008 Cambridge International Biology College Press International Publishers.
Prescott M Lansing, Harley P John and Klein A Donald 1993 Microbiology 2nd edition.Wm C Brown Publishers Dubuque, lowa Melbourne Australia.
Talaro Arthur and Talaro Kathleen, 1996 Foundations in Microbiology 2nd edition.
Wolfe .L Stephen, 1993 Molecular and cellular biology. Wadsworth publishing company Belmont California