Bacteria Are Members of Kingdom Monera

Bacteria are members of kingdom Monera and they virtually dominate all environments on earth due to their ability to grow and divide rapidly (Reece et al., 2011). Scientists and biologist believe that bacteria are the first group of living organisms to evolve on Earth (Rave and Johnson, 2001). Understanding the morphology of bacteria is essential as bacterial research provides us remarkable insights in medicine, ecology, and genetics. To study the behavior and characteristics of each and every species of the bacteria, isolation of pure culture is required.

Pure culture can be defined as a nutrient medium that consist of a single bacterial species. Isolation of pure culture is necessary to avoid any confusion in result and also to allow interpretation to be reliable. Pure cultures can be obtained by several plating techniques, which are the streak plate, spread plate, and pour plate, but only the streak plate technique will be applied in this experiment as it is much simpler way than the other techniques to obtain single bacterial species (Sumbali and Mehrotra, 2009).

In this experiment, three types of bacteria will be investigated, which are the Bacillus cereus, Escherichia coli, and Staphylococcus aureus. Once a streak plate is produced and incubated overnight at 37oC, multiple pure cultures of each bacterial colony can be produced again by identifying the appearance of each colony on the streak plate. To examine the cellular morphology of each bacterial colony, a staining method called Gram stain is required. Gram staining mainly allows the identification of Gram positive bacteria and Gram negative bacteria by staining the cell wall of the bacteria. The thickness of peptidoglycan layer in the bacterial cell wall is the main factor that determines the staining of the bacteria (Willey et al., 2011).

In the Gram staining procedure, bacterium is first treated with crystal violet and then with iodine to allow dye retention (Willey et al., 2011). Next, the bacterium is treated with alcohol, a decolourizing agent. The Gram positive bacteria will remain in purple colour, whereas Gram negative bacteria will turn colourless. Lastly, the bacterium is treated with counterstain safranin, the dye only stains Gram negative bacteria in pink or red colour, while the Gram positive bacteria remains in purple colour.