Microbiology Practical Assessment

Paper Type: 
Pages:  7
Wordcount:  1855 Words
Date:  2021-05-24

Question 2: The patients profiles are listed in Appendix A. For each patient decide whether the organism isolated significant or not highlighting the reasons for your decision. (20 marks).

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Patient A was a healthy 35-year-old man with a painful boil on the face and normal fever. The isolated microorganism is S. aureus. The isolation was significant in the sense that S. aureus is a cause for various causes of skin-related diseases and conditions including folliculitis. The above organism is commonly present in the nasal passages of the humans, and it is transported from the nasal passages to the skin. It can then enter the body through natural openings in the skin barrier, such as the hair follicle (Tortora et al. 2010). The microbes are then responsible for the infection of the hair follicle and cause the furuncle also known as the boil, which is a type of abscess, a localized region of pus surrounded by inflamed tissue.

Patient B was a 13-year-old boy presented with a fever, sore throat, difficulty swallowing and foul breath. The isolated microorganism is Beta Hemolytic Streptococci. It is responsible for causing streptococcal pharyngitis or a strep throat-an upper respiratory tract infection. Though not streptococcal infection causes all sore throats, others are caused by bacteria and viruses. Besides, local inflammation and fever characterize pharyngitis (Tortora et al. 2010).

Patient C was a 23-year-old female presented with white vaginal discharge and extreme itching of the vaginal area. The isolated microorganism is a fungus, Candida albicans. The isolation is significant because Candida albicans is the most common species, causing 85- 90% of white vaginal discharge and extreme itching of the vaginal area. It is estimated that by the age of 25, an estimated half of college women will have had at least one physician-diagnosed episode. The fungus Candida albicans is responsible for the production of a varied amount of discharge that is either white or curdy with a yeast smell.

Patient D was a 34-year-old pregnant female (second trimester) presenting with a five-day history of urinary urgency unpleasant smelling urine and a general sense of feeling unwell. The isolated microorganism was E.coli. The isolation of the bacteria was significant because approximately 70 percent of all the pregnant women develop glycosuria, a medium that encourages bacterial growth in the urine (Delzell, and Lefevre, 2000). The organisms that cause UTIs during pregnancy are similar to those found in non-pregnant patients (Tortora et al. 2010).

Patient E was a 17-year-old male recently returned from an adventure holiday in France. He presented with a painful ear that had a slight discharge. The microorganism is Pseudomonas aeruginosa, which is a causative agent for otitis externa (Tortora et al. 2010). Since he was coming back from holiday, it is significant since otitis externa is also known as the swimmers ear, a condition associated with pool-type saunas and hot tubs. When many people use these facilities, the alkalinity rises, and the chlorines become less efficient; at the same time, the concentration of nutrients that support the growth of pseudomonads increases. Hot water causes hair follicles to open wider, facilitating the entry of bacteria (Tortora et al. 2010).

Question 3: On organisms A and D and taking into account the clinical data given in Appendix 1 use your results to decide upon the most suitable treatment for the patients. Justify your choice including a brief explanation of why you have discounted the other antibiotics tested. (15 marks)

Microorganism A is S. aureus.

The treatment of the infection and prevention of recurrence may be through the use of oral antibiotics. Penicillin is an example of an antibiotic. However; penicillin is not an ideal option because of the microbes have the ability to develop resistance to it. The E test results showed that the Resistant > 0.12 to penicillins). Furthermore, they cause side effects such as for cause side effects such as diarrhea, liver problem, joint pain, and skin rash, fever as well as muscle pain. The microbes also show resistance to Tetracycline.

Mupirocin would also be ideal, but the side effects are so much and include pain, burning, itching, and stinging and skin rash. Benzocaine ointment may also be an excellent antibiotic as it is used in the treatment of boils. The local anesthetic ointment numbs the pain by obstructing transmission of the pain signal. A small amount of the ointment is sufficient for reducing the pain. However, its side effects may be fatal especially if instructions are not followed. They include respiratory failure, uneven heart rhythm, seizure, and coma.

The use of a broad-spectrum antibiotic is a welcome idea in this case. Gentamicin is referred to as a broad-spectrum antibiotic that utilized to treat boils. Ointments have gentamicin that is used to treat the infected skin. Gentamicin ointment may be used on the boils three times per day.

Microorganism D

The antibiotic that is chosen in managing the condition addresses the organism responsible for the infection and its also safe for both mother and baby (Delzell, and Lefevre, 2000). Ampicillin is commonly used, but in recent years E. coli has become increasingly resistant to ampicillin. Research has established that there is Ampicillin resistance in about 20 to 30 percent of E. coli that is cultured from urine in the outpatient setting.

Nitrofurantoin (Macrodantin) is a good choice for short duration because of its high urinary concentration. It is safe at this stage as it is contraindicated in the late third trimester because of the potential of causing hemolytic anemia due to immature erythrocyte enzyme systems (Habib, 2013).

Sulfonamides may also be ideal for the expectant mother since they are safe in the first and second trimesters. They would be detrimental in the third trimester, as they carry a risk that the infant will develop kernicterus, especially if they become preterm infants (Habib, 2013). Other common antibiotics, e.g., fluoroquinolones and tetracyclines would not be ideal for prescription during pregnancy as a result of the possible toxic effects on the fetus (Delzell, and Lefevre, 2000).

Question 4: Explain in detail the theory behind the catalase test. Your answer should not be merely a description of the process. Using the two organisms Staphylococci (aureus) and Streptococci (Beta hemolytic) as examples detail the types of organisms that require the enzyme and the cellular processes concerned. What are the limitations of the test? (10 marks)

The catalase test is used to identify the presence of catalase enzyme in bacteria and distinguishes positive and negative catalase organisms. For example, Staphylococci is catalase positive, and Streptococci is catalase negative (Leboffe and Burton, 2008). Catalase catalyzes the breakdown of hydrogen peroxide (H2O2- (toxic) into water (H2O) and oxygen (O2);

2H2O2 + Catalase 2H2O + O2

Positive catalase bacteria that are aerobes and facultative anaerobes have the ability to respire using oxygen as a terminal electron acceptor. However, negative catalase bacteria can be anaerobes or can be facultative anaerobes that only ferment and do not inhale using oxygen as a terminal electron acceptor (MacFaddin, 1985).


Organisms die at a particular time; the aerobic organisms should be taken between 18 to 24-hour old culture.

Anaerobic organisms that are growing slow, between 24 to 72 hours culture can be used, which should be exposed to ambient air for half an hour before the test begins.

Blood-containing media should not be used. Metallic loops can cause a false-positive result

Bacteria that are grown with no glucose or on low levels may lead to inconsistent outcomes from non-iron enzymes, such as pseudo-catalase results

Question 5: Explain in detail the principle of the Oxidase Test. Your answer should not be merely a description of the process. Using the two organisms E.coli and P.S. Aeruginosa as examples detail the types of organisms that require the enzyme and the cellular processes concerned. What are the limitations of the test? (10 marks).

The oxidase test is a test that is used to detect the availability a cytochrome oxidase system that will catalyze the transfer of the electrons between electron donors in the bacteria and a redox dye- tetramethyl-p-phenylenediamine. The dye is reduced and changes its color to a deep purple color (MacFaddin, 2000, p. 363).

The tests are useful for the identification of organisms that produce a cytochrome oxidase. Examples of such organisms are the Escherichia coli and Pseudomonas aeruginosa. Such organisms will produce an intracellular enzyme that will catalyze the process and turn the reagents to a deep purple color. Organisms that do not have the cytochrome oxidase in their respiratory system will not catalyze the reagent and therefore the solution will remain colorless. They are then said to be oxidase negative.

The cytochrome system can only be found in aerobic organisms, which are capable of utilizing oxygen as the final hydrogen receptor. Water or hydrogen peroxide are the end products.

For example, the analyst can confirm the presence or absence of Pseudomonas Aeruginosa as oxidase test swap reacts with bacteria and transfers into dark purple color. Such result is based on the presence of cytochrome oxidase that is found intracellular in P. aeruginosa. On the other hand, E.coli will show no change in color because it is a negative oxidase.


The usage of fresh reagent is required, due to automatically oxidizing if the reagent is older than seven days.

High level of glucose on a media that accommodated bacteria and yeast, it is required not to exceed sugar on such media.

Growing bacteria releases some dyes that can provide not accurate results

The test reagents will effectively kill the microorganisms, so sub-culturing should be done before adding any reagent to an active culture.

To produce the best results, colonies that are used should be between 18-24 hours old. The main reason is that the older colonies will produce weaker reactions.

Question 6: Which substrates are included in the chromogenic agar used in the practical and how do they aid bacterial identification?

Chromogenic UTI Agar has two chromogenic substrates cleaved by enzymes from Escherichia coli and Enterococcus spp. Besides, it has tryptophan, and phenylalanine that provide evidence the presence of Morganella spp., Providencia spp and Proteus spp. because of tryptophan deaminase activity. It is founded on deficient CLED Medium that brings an essential non-inhibitory diagnostic agar while averting the brimming of Proteus spp.

One is the X-Gluc that focuses on b-glucosidase, which is an enzyme that the E.coli bacterium produces. This help in detecting if the E-coli in the food is contaminated. The second one is the Red-Gal which is cleaved by b-galactosidase enzyme leading to pink colonies.

Question 7: Explain the principle of the Germ Tube Test and detail the main limitation associated with it. (5 marks?)

The differentiation of Candida albicans from all the other forms of yeasts is made possible by a screening test known as the Germ tube test. The formation of a germ tube is as a result of the increased synthesis of the RNA. The germ tube is one of the virulence factors in Candida Albicans. It is a rapid test that is used to identify C.albicans.

Limitations of the Germ test

There is a possibility of other species of candida such as the C. tropicalis being interpreted as germ tubes since they form pseudo hyphae.

The tests are not conclusive as it is only an overall scheme; therefore there is the need for more tests f...

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Microbiology Practical Assessment. (2021, May 24). Retrieved from https://midtermguru.com/essays/microbiology-practical-assessment

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