Know how to use a microscope to look at microorganisms. Differentiate between gr
ID: 85352 • Letter: K
Question
Know how to use a microscope to look at microorganisms. Differentiate between gram positive and gram negative under the microscope Identify the morphology of microorganisms Know aseptic techniques Motility Differentiate motile and non-motile bacteria in semi-solid media How do you know the bacteria are motile? What is the indicator in the media? Antiseptics and Antibiotics: Understand how antiseptics and antibiotics affect bacterial cells Differentiate between Antiseptics and Antibiotics How do you know they kill the bacteria? What is zone of inhibition? Define the term sensitive and resistant in terms of bacterial growth Given the size of the zone of inhibition determine if the bacteria was resistant or sensitive to the antibiotic How would you identify what antiseptic or antibiotic is most effective in killing bacteria?Explanation / Answer
ANSWERS:
Under a microscope, the gram positive bacteria will appear in purple or violet color because they take up the crystal violet dye in presence of the thick peptidoglycan cell wall which contains teichoic acid. Whereas the gram negative bacteria will stain red or pink in color due to the counter stain safranin since they do not retain the crystal violet dye. Hence, the gram negative bacteria get decolorized when washed with alcohol or the acetone during Gram’s staining.
The cell shape, structure and arrangement describes the morphology of the microorganisms under a microscope. Depending on this, the bacterial morphology is of the following types:
Aseptic techniques are lab practices and the experimental procedures performed under controlled conditions to avoid contamination with microbes. This can be done by including:
MOTILITY:
Motility of the bacteria is the organism’s ability to move. This locomotion is achieved by the flagella. Usually, the spiral and bacilli bacteria are motile and the cocci are non-motile. Their motility is observed in a semi-solid media. Non-motile bacteria grow only along the stab line but motile ones swim through the soft semi-solid agar which makes the entire tube turbid.
The dispersed growth of the bacteria in the entire tube is the indicator of motility of the bacteria in the stab.
ANTISEPSIS AND ANTIBIOTICS:
Antibiotics kill the microbes. E.g. the bacteriocidal and bacteriostatic antibiotics. This can be achieved at various stages of the life cycle of microbial growth. Whereas the antiseptics can only prevent the spread of infection by the microbe. These are used as topical disinfectants e.g. hydrogen peroxide, alcohol, iodine, potassium permanganate solution etc.
The bacteria are killed by the disruption of their cell wall. Hence, the killed bacteria do not show any sign of growth. In the lab, the bacterial culture shows a zone of inhibition around an antibiotic disc confirming that the bacteria are in the zone are killed due to the effect of the antibiotic.
The “zone of inhibition”, is a clear area around the antibiotic disc where stops the bacteria stops growing or is killed by the antibiotic. This is also known as the Kirby-Bauer Test. The size of the zone of inhibition depends on the effectiveness of the antibiotic against the bacterium. Eg. Tetracyclin being a wide spectrum antibiotic is effective against most of the bacterias.
The bacteria sensitive to the antibiotic will not show any growth whereas the resistant bacteria are the ones which will grow even in the presence of the antibiotics.
Sensitive bacteria will have a larger zone of inhibition as opposed to the resistant bacteria which will have a small size of the zone of inhibition. The resistant bacteria may not show any zone of inhibition at all.
Thus, by observing the size of the zone of inhibition of the various antibiotics placed in the petri dish, one can determine the effectiveness of the antiseptic or an antibiotic against the growing bacteria. The substance which has a larger zone of inhibition is most effective in killing the bacteria.
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