Also, according to the gram staining results along with the shape combination, the bacteria species could be identified. In this case, the observation we made was purple and long rod in appearance. Purple staining indicates gram positive from what we have learnt and only one species of bacteria matched the combination of long rod and gram positive, therefore the inference we made was “Bacillus Subtilis”. As for the second sample, we observed purple and cocci bacteria in appearance. The inference we made for this was the “Staphylococcus Albus” because there was only one combination with gram positive and cocci shaped bacteria that matched our observation in the results table provided.
I have performed gram staining, antibiotic susceptibility, MacConkey plates and catalase test to identify the species of bacteria present in samples A and B, which I had been allocated. The first experiment I had carried out was “gram staining”, which I found to be the most useful of all. The reason behind this is because when the slides with bacteria samples were placed under the microscope, they were easily identified. The results for sample A was that the shape of the bacteria were long rod and the colour was purple (we know that the colour purple is stained on gram positive bacteria); there was only one specie that matched our observations, which was the Bacillus subtilis. Similarly, sample B was observed as purple and cocci shaped; this was easily identified because again there was only one expected result that matched the observations and that was Staphylococcus albus.
The MacConkey plate test was the second confident test I carried out. In the results for sample A, I observed no growth, however there are two expected samples that match this, they are: Bacillus subtilis and Lactobacillus bulgaricus. From these results further identification was necessary for sample A, but considering the gram staining test, Bacillus subtilis was the specie of bacteria I elected from the two expected results. As for sample B, the only result was poor growth in the MacConkey plates, therefore the inference made straight away was Staphylococcus albus.
When it comes to the catalase test, I found this quite unnecessary due to the fact that it did not really aid the identification of my samples. I already had identified, sample A as Bacillus subtilis and sample B as Staphylococcus albus; and they both had given a positive result, meaning bubbles occurred. I would have only eliminated Lactobacillus bulgaricus from my expected results and that would have been helpful if I hadn’t began the tests from gram staining.
Finally, for the antibiotic susceptibility test, the results for sample A were that it was sensitive towards all the antibiotics which we had used in the test, there was one expected result that could have matched this observation and that was Staphylococcus albus, which is also sensitive towards all the antibiotics. Whereas, sample B showed no proper growth and made it difficult for us to observe the inhibition zones and come up with a result. However, from the previous tests we had already identified sample A as Bacillus subtilis although it is resistant towards Fusidic Acid and Penicillin G.
Overall, I am confident enough with the final identifications of the samples although there were some errors made, but we exterminated most of them by using sterile technique throughout the operation of preparing the plates and slides. There were contradictions we came across, such as the antibiotic susceptibility test as mentioned above. The conclusion that I can make is, I would recommend the antibiotics Chloramphenicol, Erythromycin, Oxacillin, Novobiocin, Streptomycin and Tetracycline to the patients of sample A.
Furthermore, to confirm the identification of Bacillus subtilis, a “starch hydrolysis” test could be performed. Bacillus subtilis will have a zone of clearing in the plate where starch is spread out; the zone will indicate that the starch is broken into maltose and glucose.
As for Staphylococcus albus, there is a confirmation test that could be performed. However, I have used its substitute “Staphylococcus aureus” to determine the results of the further tests. The coagulase test will determine Staphylococcus aureus from Staphylococcus epidermidis. When clotting is observed at the bottom of the broth in one of the test tubes- one test tube holds Staphylococcus aureus and the other holds Staphylococcus epidermidis- that test tube is identified as holding Staphylococcus aureus. The reason behind this is the Coagulase enzyme clots the plasma used as the reagent in order to prevent an attack by the defences of the host.