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Lab Report
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Identification of Gram Negative Bacteria (Lab Report Sample)


this was a laboratory report in which the client was supposed to discuss a certain set of results obtained in a practical experiment.


Identification of Gram Negative Bacteria
Laboratory Report
The main objective of this experiment was to distinguish between Escherichia coli and Klebsiella pneumoniae cultures. The system of distinguishing the two involved using morphological characteristics and biochemical tests. Morphological characteristics that were exhibited in this experiment were colony characteristics and motility. E. coli colonies were found to have rough margins while those of K. pneumonia had smooth edges. E. coli lacked the capability to utilize citrate under anaerobic conditions. The ability of bacteria to develop resistance to antibiotics was highlighted. The main reason for the emerging mutations and consequent resistance to drugs is the overuse of antibiotics. It was agreed that the best method to tell the two species apart was by using quick methods such as motility. Other methods such as citrate utilization are expensive and not capable of delivering producible results.
Identification of Gram Negative Bacteria.
Laboratory Report.
The main difference between gram- positive and gram- negative bacteria is there appearance below the light microscope after performing the gram staining procedure. At X100 magnification with the aid of immersion oil, gram -positive bacteria appear to dark blue due to the crystal violet stain. Gram- negative bacteria on will appear red because they take up the safranin counter stain. The primary principle behind these differences is due to the difference in the thickness of the peptidoglycan layer of these bacteria (Claus, 1992). Gram- positive bacteria have a thicker peptidoglycan layer and are therefore able to retain the crystal violet stain once washed with ethyl alcohol. Gram- negative bacteria have a thinner peptidoglycan layer that cannot withstand a wash by ethyl alcohol. When safranin is applied to both groups, the Gram- positive bacteria will not take it up because its peptidoglycan is already saturated with crystal violet. On the other hand, the gram- negative bacteria will readily take up the counter stain because the primary stain (crystal Violet) was washed off with ethyl alcohol.
Due to the importance associated with their identification, it is crucial that students acquire skills necessary for telling apart these bacterial groupings. Students ought to learn how to use various biochemical tests to identify gram- negative bacteria to the species level. More often than not, it requires a lot of practice to acquire such skills. A misidentification of a gram- negative species can turn fatal or ineffective in the event that the doctor prescribes specific antibiotics following a false laboratory finding. Experiments such as this one are fundamental in imparting basic laboratory skills. Students also gain first -hand experience unlike when they read these tests in books. In this regard, it is important that students learn about the biochemical tests that are currently in use during the identification of gram- negative bacteria species. This particular experiment encompasses a set of biochemical tests that distinguish between various gram- negative bacteria such as Glucose Oxidation Function, indole utilization, and citrate utilization. Other features used to tell apart gram -negative bacteria include morphology, anaerobic growth and colony characteristics.
Materials and Methods
1 Cultures- Escherichia coli and Klebsiella pneumonia, Moraxella as a control and young peptone water cultures for motility tests.
2 Oxidase strips
3 Sterile toothpicks
4 Reagents for MR and VP tests
5 Peptone water
6 Urea agar slopes
7 Kligler iron agar
8 Simmons citrate medium and sterile saline
9 Ornithine and lysine decarboxylase medium and base broth + sterile paraffin
10 Indole reagent and filter paper strips.
Identification tables for bacteria.


K. pneumoniae

Colony features
Anaerobic growth

O2, 370C, 24 hours (Conditions)
Large colonies
Irregular margins
Glossy/ shiny
O2, 37OC, 24 hours (conditions)

O2, 37oC, 24 hours
Large colonies
Smooth margins
O2, 37OC, 24 hours
Comparatively larger
Lighter center
Not tested.
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