Microbiology Case Study

Microbiology Case Study Case 1 1. The most likely diagnosis is legionella pneumonia.

2. Gram staining was done to help identify the causative bacterium. The test differentiates gram negative bacteria from gram-positive bacteria based on their staining characteristics. The bacteria are gram-negative as it stained pink, taking the color of the counterstain used.

3. Legionella pneumonia requires L-cysteine, amino acids and iron salts to grow in culture media.

The preferred culture medium for the bacteria is buffered charcoal-yeast extract - αketoglutarate. The medium contains yeast extract, iron, L-cysteine, and α-ketoglutarate and has a pH of 6.9. Activated charcoal in the media removes peroxides that form in the media (Chahin & Opal, 2017). Legionella pneumonia is aerobic and requires an optimum temperature of 360c for in-vitro growth.

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4. Legionella pneumonia can be effectively treated using antibiotics. Macrolides (azithromycin), and the quinolones (moxifloxacin, ciprofloxacin, gemifloxacin, levofloxacin, trovofloxacin) are the most potent antibiotics of choice being used. Macrolides are bacteriostatic and works by inhibiting bacterial protein synthesis. Quinolones inhibits bacterial DNA synthesis.

Case 2 1. The most likely diagnosis is shingles, caused by varicella-zoster virus.

2. Varicella-zoster virus is classified under the herpes viruses and is responsible for chicken pox in children and shingles as a recurring disease in adults. It is a linear, double stranded, enveloped, DNA virus.

3. The virus replicates within the host’s nucleus. The virus first attaches itself onto the cell membrane to initiate infection. It then penetrates the membrane and uncoats to release its genome. The transcription and translation process then follows. In herpes viruses, the viral DNA is transcribed onto the cell’s mRNA, causing the replication of viral DNA and the transcription of viral genes. Viral assembly then occurs within the nuclei and the virions are then released by cytolysis.

4. The common risk factor for developing shingles is being immunocompromised or immunosuppressed. Shingles occurs as a recurrence after an initial chicken pox infection. Its occurrence is triggered by immunosuppression from chronic diseases, immunosuppressive medications and organ transplant. It is also more common in older adults than other patient groups.

Case 3 1. The most likely diagnosis is malaria, caused by plasmodium falciparum

2. The patient had history of travel to malaria endemic zones including east Africa, where P. falciparum is endemic. His blood smear shows the ring stage of P. falciparum.

3. The disease was acquired through a mosquito bite by an infective female Anopheles mosquito.

4. Malaria sporozoites are introduced into the body by a mosquito during a blood meal. The sporozoites infect liver cells where sexual reproduction takes place and the parasites mature into schizonts. Schizonts rapture to release merozoites, which invades the blood stream. Asexual reproduction takes place in red blood cells where trophozoites mature into schizonts, which raptures to release merozoites that differentiate into sexual gametocytes. The gametocytes are ingested by the mosquito during a blood meal for the sporogonic cycle that takes place in the mosquito. The male and the female gametes mate, forming zygotes, which develops into ookinetes then oocysts that finally raptures to release sporozoites. The sporozoites are introduced to humans to initiate the malaria cycle (Gautam et al., 2020).

Case 4 1. The incubation period was from 18th to 24th of august to 22nd to 28th of September. This represents the period between possible exposure causative agents to the peak of the epidemiology curve.

2. The incidence rate of disease is determined by dividing the number of new cases of a disease by the number of persons at risk (Mishra, 2018). Hence, the incidence is 14 divided by 15, which is 0.93.

3. The severity of the disease is determined by its impact based on morbidity, mortality, and resource utilization. The duration of an illness is described as either acute or chronic depending on how long the condition lasts. Acute conditions are short-lived, whereas chronic conditions last for longer periods of time.

4. Humans are the sole reservoirs of the mumps virus.

References Chahin, A., & Opal, S. M. (2017). Severe pneumonia caused by Legionella pneumophila: Differential diagnosis and therapeutic considerations. Infectious disease clinics of North America, 31(1), 111.

Gautam, P. K., Prajapati, B., & Sujatha, R. (2020). Chapter-5 Life Cycle, Pathogenesis and Laboratory Diagnosis of Malaria Parasite. Chief Editor Dr. Durgadas Govind Naik, 105, 105.

Mishra, A. (2018). Basics of Epidemiology-Concepts made simple. Notion Press.