MICR 302 - CASE STUDY REPORTS, Winter 2012
The class will include ten Case Study and Questions, taken from Medial Microbiology,
6th edition, to help students learn and understand the pathogenic bacteria. You may earn
a total of 100 points in lecture for the Case Study Reports.
Students are encouraged to work together and discuss the Case Study and Questions, but
each student is individually responsible to write a written report on the Case Study
Questions. To copy from a textbook or another student’s report is plagiarism and in
violation of the honor code and the spirit of learning at the University.
The report will consist of your response to each question (1-3 sentences) and 1-2 pages
type written. The report is to be turned in lecture class and reports will not be accepted
late or by email. Each report will be evaluated for content and written communication
and may earn 10 points.
CASE STUDY
1 – Staphylococcus
WRITTEN REPORT DUE
Jan. 17
2 – Streptococcus
Jan. 24
3 – Enterobacteriaceae
Jan. 26
4 – Pseudomonas
Feb. 7
5 – Francisella
Feb. 14
6 – Bacillus
Feb. 16
7 – Mycobacterium
Feb. 23
8 – Clostridium
Mar. 1
9 – Chlamydia
Mar. 8
10 – Legionella
Mar. 13
.
CASE STUDY 1 – Staphycoccus
An 18-year-old man fell on his knee while playing basketball. The knee was painful, but
the overlying skin was unbroken. The knee was swollen and remained painful the next
day, so he was taken to the local emergency department. Clear fluid was aspirated from
the knee, and the physician prescribed symptomatic treatment. Two days later, the
swelling returned, the pain increased, and erythema developed over the knee. Because
the patient also felt systemically ill and had an oral temperature of 38.8°C, he returned to
the emergency department. Aspiration of the knee yielded cloudy fluid, and cultures of
the fluid and blood were positive for S. aureus.
1. Name two possible sources of this organism.
2. Staphylococci cause a variety of diseases, including cutaneous infections, endocarditis,
food poisoning, SSSS, and TSS. How do the clinical symptoms of these diseases differ
from the infection in this patient? Which of these diseases are intoxications?
3. What toxins have been implicated in staphylococcal diseases? Which staphylococcal
enzymes have been proposed as virulence factors?
4. What is the antibiotic of choice for treating staphylococcal infections? (Give two
examples.)
CASE STUDY 2 – Streptococcus
A 62-year-old man with a history of chronic obstructive pulmonary disease (COPD)
came to the emergency department because of a fever of 40°C, chills, nausea, vomiting,
and hypotension. The patient also produced tenacious, yellowish sputum that had
increased in quantity over the preceding 3 days. His respiratory rate was 18 breaths/min,
and his blood pressure was 94/52 mmHg. Chest radiographic examination showed
extensive infiltrates in the left lower lung that involved both the lower lobe and the
lingula. Multiple blood cultures and culture of the sputum yielded S. pneumoniae. The
isolate was susceptible to cefazolin, vancomycin, and erythromycin but resistant to
penicillin.
1. What predisposing condition made this patient more susceptible to pneumonia and
bacteremia caused by S. pneumoniae? What other populations of patients are susceptible
to these infections? What other infections does this organism cause, and what
populations are most susceptible?
2. What infections are caused by S. pyogenes, S. agalactiae, and viridans streptococci?
3. S. pyogenes can cause streptococcal toxic shock syndrome. How does this disease
differ from the disease produced by staphylococci?
4. What two non-suppurative diseases can develop after localized S. pyogenes disease?
CASE STUDY 3 – Enterobacteriaceae
A 25-year-old previously healthy woman came to the emergency room for the evaluation
of bloody diarrhea and diffuse abdominal pain of 24 hours’ duration. She complained of
nausea and had vomited twice. She reported no history of inflammatory bowel disease,
previous diarrhea, or contact with other people with diarrhea. The symptoms began 24
hours after she had eaten an undercooked hamburger at a local fast food restaurant.
Rectal examination revealed watery stool with gross blood. Sigmoidoscopy showed
diffuse mucosal erythema and petechiae with a modest exudation but no ulceration or
pseudomembranes.
1. Name four genera of Enterobacteriaceae that can cause gastrointestinal disease. Name
two genera that can cause hemolytic colitis.
2. What virulence factor mediates this disease?
3. Name the five groups of E. coli that can cause gastroenteritis. What is characteristic of
each group of organisms?
4. Differentiate between disease caused by S. typhi and that caused by S. sonnei.
CASE STUDY 4 – Pseudomonas
A 63-year-old man has been hospitalized for 21 days for the management of newly
diagnosed leukemia. Three days after the patient entered the hospital, a urinary tract
infection with Escherichia coli developed. He was treated for 14 days with broadspectrum antibiotics. On day 21 of his hospital stay the patient experienced fever and
shaking chills. Within 24 hours he became hypotensive, and ecthymic skin lesions
appeared. Despite aggressive therapy with antibiotics, the patient died. Multiple blood
cultures were positive for P. aeruginosa.
1. What factors put this man at increased risk for infection with P. aeruginosa?
2. What virulence factors possessed by the organism make it a particularly serious
pathogen? What are the biologic effects of these factors?
3. What antibiotics can be used to treat P. aeruginosa?
4. What diseases are caused by S. maltophila? A. Baumanni? M. catarrhalis?
CASE STUDY 5 – Francisella
A 27-year-old man was mowing his field when he ran over two young rabbits. When he
stopped his mower, he realized that two other rabbits were dead in the unmowed part of
the lawn. He removed all the rabbits and buried them. Three days later he developed a
fever, muscle aches, and a dry, nonproductive cough. Over the next 12 hours he got
progressively sicker and was transported by his wife to the area hospital. Results of a
chest x-ray showed infiltrates in both lung fields. Blood cultures and respiratory
secretions were collected, and antibiotics were initiated. Blood cultures became positive
with small gram-negative rods after 3 days of incubation, and the same organism grew
from the respiratory specimen that was incubated onto BCYE agar.
1. What test should be performed to confirm the tentative diagnosis of Francisella
tularensis?
2. This infection was presumably acquired by inhalation of aerosolized contaminated
blood. What are the most common sources of F. tularensis infections and the most
common routes of exposure?
3. What is the different clinical manifestations of F. tularensis?
CASE STUDY 6 – Bacillus
A 56-year-old female postal worker sought medical care for fever, diarrhea, and vomiting.
She was offered symptomatic treatment and discharged from the community hospital
emergency department. Five days later she returned to the hospital with complaints of
chills, dry cough, and pleurtic chest pain. A chest radiograph showed a small right
infiltrate and bilateral effusions but no evidence of a widened mediastinum. She was
admitted to the hospital, and the next day her respiratory status and pleural effusions
worsened. A computerized tomographic (CT) scan of her chest revealed enlarged
mediastinal and cervical lymph nodes. Pleural fluid and blood was collected for culture
and was positive within 10 hours for gram-positive rods in long chains.
1. The clinical impression is that this woman has inhalation anthrax. What tests should
be performed to confirm the identification of the isolate?
2. What are the three primary virulence factors found in B. anthracis?
3. Describe the mechanisms of action of the toxins produced by B. anthracis?
4. Describe the two forms of B. cereus food poisoning? What toxin is responsible for
each form? Why is the clinical presentation of these two diseases different?
CASE STUDY 7 – Mycobacterium
A 35-year-old man with a history of intravenous drug use entered the local health clinic
with complaints of a dry, persistent cough; fever; malaise; and anorexia. Over the
preceding 4 weeks, he had lost 15 pounds and experienced chills and sweats. A chest
radiograph revealed patchy infiltrates throughout the lung fields. Because the patient had
a nonproductive cough, sputum was induced and submitted for bacterial, fungal, and
mycobacterial cultures, as well as examination for Pneumocystis organisms. Blood
cultures and serologic tests for HIV infection were performed. The patient was found to
be HIV positive. The results of all cultures were negative after 2 days of incubation;
however, cultures were positive for M. tuberculosis after an additional week of
incubation.
1. What is unique about the cell wall of mycobacteria, and what biologic effects can be
attributed to the cell wall structure?
2. Why is M. tuberculosis more virulent in patients with HIV infection than in non-HIVinfected patients?
3. What is the definition of a positive skin test (PPD) result for M. tuberculosis?
4. Why do mycobacterial infections have to be treated with multiple drugs for 6 months
or more?
CASE STUDY 8 – Clostridium
A 61-year-old woman with left-sided face pain came to the emergency department of a
local hospital. She was unable to open her mouth because of facial muscle spasms and
had been unable to eat for 4 days because of severe pain in her jaw. Her attending
physician had noted trismus and risus sardonicus.
The patient reported that 1 week before presentation, she had incurred a puncture
wound to her toe while walking in her garden. She had cleaned the wound and removed
small pieces of wood from it, but she had not sought medical attention. Although she had
received tetanus immunizations as a child, she had not had a booster vaccination since
she was 15 years old. The presumptive diagnosis was made.
1. How should this diagnosis be confirmed?
2. What is the recommended procedure for treating this patient? Should management
wait until the laboratory results are available? What is the long-term prognosis for this
patient?
3. Compare the mode of action of the toxins produced by C. tetani and C. botulinum.
4. C. difficile causes what diseases? Why is it difficult to manage infections caused by
this organism?
CASE STUDY 9 – Chlamydia
A 22-year-old man came to the emergency department with a history of urethral pain and
purulent discharge that developed after he had sexual contact with a prostitute. Gram
stain of the discharge revealed abundant gram-negative diplococci resembling Neisseria
gonorrhoeae. The patient was treated with penicillin and sent home. Two days later, the
patient returned to the emergency room with a complaint of persistent, watery urethral
discharge. Abundant white blood cells but no organisms were observed in Gram stain of
the discharge. Culture of the discharge was negative for N. gonorrhoeae but positive for
C. trachomatis.
1. Why is penicillin ineffective against Chlamydia? What antibiotic can be used to treat
this patient?
2. Describe the growth cycle of Chlamydia. What structural features make the EBs and
RBs well suited for their environment?
3. Describe the differences among the three species in the family Chlamydiaceae that
cause human disease.
CASE STUDY 10 – Legionella
A 73-year-old man was admitted to the hospital because of breathing difficulties, chest
pain, chills, and fever of several days’ duration. He had been well until 1 week before
admission, when he noted the onset of a persistent headache and a productive cough. The
patient smoked two packs of cigarettes a day for more than 50 years and drank a six-pack
of beer daily; he also had a history of bronchitis. Physical examination results revealed
an elderly man in severe respiratory distress with a temperature of 39ºC, pulse of 120
beats/minute, respiratory rate of 36 breaths/minute, and blood pressure of 145/95 mm Hg.
Chest radiograph revealed an infiltrate in the middle and lower lobes of the right lung.
The white blood cell count was 14,000 cells/mm3 (80% polymorphonuclear neutrophils).
Gram stain of the sputum showed neutrophils but no bacteria, and routine bacterial
cultures of sputum and blood were negative for organisms. Infection with Legionella
pneumophilia was suspected.
1. What laboratory tests can be used to confirm this diagnosis? Why were the routine
culture and Gram-stained specimen negative for Legionella organisms?
2. How are Legionella species able to survive phagocytosis by the alveolar macrophages?
3. What environmental factors are implicated in the spread of Legionella infections?
How can this risk be eliminated or minimized?