MICROBIOLOGY Case Study
A. Infections of the Skin, Eyes, and Underlying Tissues
It was so exciting! Caitlyn was the only freshman girl selected for Varsity Singers, her high school’s touring show choir. Their summer “retreat” was a six-day mega-rehearsal to learn all of the choreography for their upcoming show season. Monday through Saturday the week before school resumed, the 28 performers danced from 8 A M to 8 P M in their un-air-conditioned gymnasium. Caitlyn didn’t particularly mind the hot, humid rehearsal conditions, but sweating profusely in dance leotards every day was really starting to aggravate the acne on her shoulders and back. After a special preliminary performance for their families on Saturday night, Caitlyn showered and dressed to go home. It was then she discovered a very large, angry “pimple” that rubbed uncomfortably on the back waistband of her jeans. By morning, it was raised and the size of a dime. Caitlyn’s mother washed the affected area, cleansed it with hydrogen peroxide, and applied an antibiotic ointment, telling her they
would call the doctor tomorrow if it didn’t improve.
1. What possible infections might Caitlyn have?
2. What microbes would normally cause these infections? Are these microorganisms normal skin
flora, pathogens, or both? Explain.
Monday morning, the first day of school, Caitlyn’s back was sore. “A great way to start high school,” she thought. Caitlyn’s mother took her to the pediatrician’s office right after school. The PA examined her back and was alarmed to see a lesion almost two inches in diameter. It was tender to the touch with poorly demarcated margins. The region was raised, warm, and Erythematous (reddened) with several smaller red lines radiating outward.
3. What is your diagnosis? Describe the nature of this condition.
After consulting with the pediatrician, Keflex was prescribed for Caitlyn. She was sent home with instructions to monitor the infection. If it was not obviously improved by the next day, she was to return for reevaluation.
4. To what class of antibiotics does Keflex belong? How does this drug work? What group of microbes is especially susceptible to it?
On Tuesday morning, Caitlyn went immediately to see her pediatrician. The lesion was the size of an egg and quite sore. Caitlyn also presented with a temperature of 38.4°C (101.2°F). Motrin and compresses were advised as comfort measures. The Keflex was continued and the lesion cultured for laboratory analysis. Again, she was told to return if she didn’t notice improvement.
5. How would you collect a specimen from Caitlyn’s lesion? Name several types of transport media commonly used. Why is it so important to appropriately transport a specimen to the microbiology laboratory?
6. What media will likely be inoculated when this sample arrives in the laboratory? State your reason(s) for choosing the media you’ve indicated.
7. In addition to media inoculation, what other procedure will be performed immediately using the specimen?
The preliminary Gram stain of the specimen showed many Gram-positive cocci in clusters. After 24 hours, the TSA with 5% sheep blood plate demonstrated pure growth of small, round, smooth, white, gamma-hemolytic colonies. The same colony morphology was observed on the PEA (or CNA) plate with zero growth on the EMB (or MacConkey) plate. Colonies were also observed on the MSA plate, which was completely pink in color.
8. What is meant by the term “pure growth”? What does it say regarding the quality of your specimen collection?
9. Based upon these laboratory results, what microbe do you predict is causing Caitlyn’s infection? Explain. What two chemical tests would you perform next to verify your answer?
Colonies from the TSA plate were suspended in sterile saline and introduced into the Vitek II analyzer. It confirmed Staphylococcus epidermidis was the pathogen involved and indicated Keflex sensitivity.
MICROBIOLOGY Case Study