17SS MLSC4071 Advanced Clinical Correlations

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Name: _____________________ _____________

Module 12: Microbiology I Assignment Instructions: Answer the following questions. Follow the guidelines in the course syllabus for proper submission of your document. All references, including course materials, must be cited using APA guidelines at the end of the document. If the answer was found in course materials, a citation is required. If a direct quote is used, the reference should be cited using APA style. Failure to follow the citation directions will result in a deduction of 10% of the possible assignment points. Grading: A total of 49 points will be converted to 20 points for this assignment. Due Date: Thursday, April 6th at 11:55 PM (EST) Part 1 – Cases Case #1 A 53-year-old male farmer presents for evaluation of a growth on his arm. About a week previously, he noticed some mildly itchy red bumps on his arm. They started to blister a day or two later and then ruptured. During this time he had a low-grade fever, but otherwise felt well. Further questioning reveals that he has had no ill contacts and never had anything like this before. He has cows, horses, goats, sheep and chickens on his farm. On examination of his right upper arm, there is seen a 4.5-cm circular black eschar surrounded by several vesicles (blisters) and edema. He has tender axillary lymph node enlargement (adenopathy). A gram stain and culture of fluid drained from a vesicle is shown below in image 1 and image 2 respectively.

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Image 1 

        

Image 2

1. Describe the gram stain and culture morphology in images 1 and 2. (1 point)

2. What is the structure indicated by the arrow? How could these structures be more easily visualized? (1 point)

3. What organism is the likely cause of this disease? (2 points)

4. What test would you suggest be done to supplement the identification? (1 point)

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5. What are the primary virulence factors of this organism? (2 points) 6. What is the recommended treatment for this disease? (1 point)

Case #2

A 65-year-old white male with a history of schizoaffective disorder was brought to the emergency room with a 24-hour history of difficulty breathing. Laboratory studies showed leukopenia (leukocytes = 1.66 × 109/L), mild thrombocytopenia (115,000 platelets/mm3), hypoxemia (PaO2/FiO2 = 61), and lactic acidosis (pH = 7.29, lactate = 4.45 mmol/L). Empirical antibacterial chemotherapy was started on admission, and mechanical ventilation was immediately necessary. A chest radiograph showed diffuse alveolar infiltration of both lungs, without pleural effusion. A preliminary gram stain of his sputum was performed and the specimen was cultured. A nasal specimen was reported positive for influenza by polymerase chain reaction. On day 3, the patient's condition deteriorated and, at 2:50 AM, the patient suffered a cardiac arrest and could not be resuscitated. Initial gram stain of sputum: (Image 1)

  

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24 hours after incubation the following growth was noted on blood agar incubated aerobically:

Culture (Image 2)

Gram stain of aerobic isolate (Image 3) Catalase test of aerobic isolate (Image 4)

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1. Describe the colony morphology (Image 2), gram stain (Image 3) of the culture and the results of the catalase test (Image 4). (1.5 pts) 2. Based on the initial results, what test should be done next to identify this species? Give the principle of the test. Include a description of both forms. (2.5 pts) 3. What is the most likely genus and species of the causative organism? (2 pts) 4. How is this infection usually treated and what significant problem with this organism could arise in the treatment? (1.5 pts) 5. How would suspected cases of infection caused by the strain of this organism referred to in the previous question be identified in a clinical laboratory? (specify a characteristic different than described in the previous question) (1 pt)

6. The organism was found to be PVL positive. What is PVL and describe the mechanism by which it affects the virulence of this organism? (1.5 pt) 7. The patient also had an influenza viral infection. Did that contribute to the severity of the bacterial infection? Explain (1 pt) Case #3 A 48-year old male experienced severe dizziness and was transported to the emergency room. He reported feeling very weak and he had a headache intermittently since he had a tooth extracted four days prior. His blood pressure was normal but upon examination a pronounced heart murmur was heard and tiny petechial hemorrhages were found under the fingernails. He was in general good health but had rheumatic fever about 15 years ago.

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A blood culture was ordered.

   Image 1 Sub culture of significant isolate on blood agar (24 hr growth) 

Image 2: Gram stain of significant isolate

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Image 3: Catalase test of significant isolate

   Image 4: 24 hr growth of significant isolate with P disk.

    Image 5 Bile Solubility test of significant isolate

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   Image 6 PYR test of significant isolate 1. Based on the case history what is the most likely cardiovascular condition? Was the finding of petechial hemorrhages under the fingernails significant and what causes them? (1.5 pts) 2. Describe the gram stain and culture morphology (Images 1 and 2). (1 pt) 3. What is the P disk in Image 4? Describe this test and state the results in this case. (1.5 pts) 4. Describe the PYR test and give the results (Image 6) for this case? (1 point) 5. What is the most likely causative agent in this case? (2 pts) 6. What tests can be performed to further speciate this organism? (1 pt) 7. What is the most likely route of transmission in this case? (1 pt) 8. Is there any connection between the current infection and the patient’s previous rheumatic fever? Explain your answer. (1pt)

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Case #4

A 57 year old woman was admitted due to a meningeal hemorrhage. She required prolonged mechanical ventilation due to respiratory failure. After one month she was weaned from the respirator but a progressive internal hydrocephalus required a ventriculo-peritoneal shunt. Symptoms of a sub-acute infection appeared in the following week and progressively worsened. However, blood and urine cultures remained negative and no pathogen was found in the sputum culture. CSF obtained from the ventricular shunt showed 25 wbcs with 50% PMNs and a 65.0 mg/dL albumin level (normal= 15- 50 mg/dL). The culture, gram stain and biochemical results are shown below. Image 1: 24 hr culture of CSF from shunt on BA  

Image 2: Gram stain of isolated organism

   

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Image 3: Catalase test of significant organism Image 4: Coagulase test of significant

organism    

Image 5: Modified oxidase test   Image 6: Bacitracin susceptibility (Microdase) of significant organism test of significant organism 1. Describe the gram stain and culture morphology (Image 1 and 2). (1 pt) 2. Give the results of the biochemical tests (Images 3-6). (2 pts) 3. For each of the biochemical tests in this case (Images 3-6), list a positive and negative control organism? (2 pts) 4. Describe the principle of the modified oxidase test. How does the modified oxidase test help to confirm the presumptive ID of the isolate? (1.5 pts) 5. What is the most likely causative organism in this case? (2 pts)

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6. Define saprophytic. Are saprobes typically pathogenic? (1 pt) 7. Define opportunistic. Is the likely causative agent in this case considered opportunistic? What conditions in the patient contributed to the cause of this infection? (1.5 pts) Case #5 A three-year old female presented to the emergency room with a fever of 38.6°C. Her father had made her eat some cereal for breakfast, but she had vomited it immediately afterwards. She appears to be lethargic and not very well kempt. It is noted that there are several bruises on her forearms. Preliminary examination reveals a moderately red throat with white to yellow-gray tonsillar patches, a clear chest, and bilaterally enlarged cervical lymph nodes. Because she is mildly dehydrated, she is admitted to the hospital. The patient’s vaccination history is not available. 1. What is the most common bacterial cause of sore throat/pharyngitis? (1 point) A presumptive diagnosis is made based on the most common cause of pharyngitis and the child is started on penicillin. The child does not improve in spite of the penicillin. On the third hospital day it is noted that she is extremely lethargic and is having trouble breathing. An examination of her throat reveals a grayish-yellow exudate covering her trachea. It is noted that it is tough, almost like a piece of chamois leather. A gram stain from a throat culture is shown below.

   Image 1:Gram stain of significant isolate  

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2. Does the gram stain support the presumptive diagnosis? What other organisms are suspected? What characteristics on the gram stain were influential in your decision? (2 points)   3. What is the best media for growth of this organism? What is the appearance of the organism on this media? (2 points) The results of further tests are shown below.

   Image 2: Catalase

  Image 3: Urease Image 4: Nitrate reduction test           4. List the results of the further tests shown above (Images 2-4). Are these results consistent with the organism identified in question #2? (2 points) 5. Briefly describe a test for the toxigenicity of this organism. (1 point) 6. How could this child's infection have been prevented? (1 point)