MICROBIOLOGY

Case Study a

1. 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.

1. 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.

1. 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. 

1. 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?
2. What media will likely be inoculated when this sample arrives in the laboratory? State your reason(s) for choosing the media you’ve indicated.
3. 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.

1. What is meant by the term “pure growth”? What does it say regarding the quality of your specimen collection?
2. 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.

HATS Off to MRSA b

They had toyed with the idea for years, and now, Jacob, Tony, and Tom had finally made their dream of a family business a reality. With Jacob’s computer expertise, Tom’s experience from his marketing internship, and Tony’s apprenticeship with a master painter, the three brothers were confident that “Color Your World Painters, Inc.” would be a successful business venture. After only six months, their Internet and local TV advertising had made them a household name in their community. Tony had to hire additional painters to handle their burgeoning workload. The brothers moved to a larger office, purchased improved equipment, and issued all employees uniforms and painter’s caps with their flashy new logo.

Business that summer was booming. The hot, sweaty paint crew worked from sun up to sun down every day. Upon returning to headquarters, they hung their caps on the wall, changed out their uniforms for street clothes, and collected nice fat paychecks. Jacob boasted smugly that things couldn’t be better…until one morning Tony didn’t show up for work. Annoyed, Jacob grabbed a uniform and Tony’s hat, got the painters organized, and took his brother’s place on the work crew while Tom tried to track down Tony. Tom’s second phone call reached his five-year-old niece, who was answering her mother’s cell phone. In a small and tearful voice, she told her uncle that they were at the hospital and daddy was

very sick because he had slime leaking out of his head. Confident that his niece’s imagination had run away with her, Tom reassured the little girl and told her he would be right there. Tom left a voicemail message on Jacob’s cell phone and headed to the hospital. When he met his sister-in-law, Julia, Tom was shocked to find his brother was in surgery. Stunned, Tom listened to Julia describe the events of the last few days. Out of embarrassment, Tony never mentioned to his brothers that he periodically suffered from boils around his hairline when working under hot, humid conditions. Two days ago, when Tony noticed the first few boils appear, he assumed it was just a recurrence of his seasonal problem. But, after 24 hours, Tony was becoming concerned. This was the worst case he had ever experienced. He had at least a dozen boils on the back of his neck and into his hairline. Despite his discomfort, Tony continued work without complaint, although he secretly blamed his problem on wearing the new company cap that made him sweat more around his hairline.

That evening, Tony showed Julia his neck and asked her to help him disinfect and bandage the area. His frightened wife pleaded with him to go to the emergency room, but Tony flatly refused. Number one, they didn’t have health insurance and he certainly did want to run up a bill. But number two, Tony was not about to be humiliated by going to the hospital for something so simple. In his mind, boils could hardly be considered life-threatening. Julia gently cleansed the area for her husband, counting 13 boils the size of a dime or larger. Tony winced in pain.

1. What microbes commonly cause boils?
2. What is another name for a boil?
3. What is the incubation time for boil development?
4. What factors are facilitating Tony’s problem?
5. What at-home cleansing and treatment options would you have recommended Julia try?

line. Tony found it humorous that his “gooey zits” got quick attention at an ED known for its long wait times. Dr. Bergmann, an infectious disease physician, examined Tony, noting heat, extreme erythema, folliculitis, 15 boils ~1–2 cm in diameter, some draining copious amounts of pus, and numerous seeping  ulcerations. Dr. Bergmann applied a topical anesthetic before lancing several boils for culture. He ordered four sets of blood cultures drawn, started broad spectrum IV antibiotics, and immediately scheduled Tony for surgical debridement of his infection.

1. Why did the doctor lance boil to collect a specimen for culture when many others were already draining pus?
2. Why did Dr. Bergmann start Tony on antibiotics even though he didn’t know the microbe involved or its drug sensitivity?
3. Why were blood cultures ordered?
4. Why was Tony a candidate for immediate surgery?

Tom and Julia sat for about an hour in the waiting room before Dr. Bergmann arrived with an update on Tony’s condition. Preliminary Gram stain results from the lab confirmed Gram-positive clusters of cocci in Tony’s boils. Due to the extensive tissue damage, Dr. Bergmann confided to the family that he suspected community acquired-MRSA. Although Tony was “resting uncomfortably,” the surgical debridement of a 3.5 cm  10 cm area was a success. Tony would receive a three-week course of IV vancomycin before being permitted to return to work.

1. What common skin microbes demonstrate this Gram morphology and staining?
2. What does MRSA stand for?
3. What is the difference between community acquired-MRSA and hospital acquired-MRSA?
4. How does the resistance demonstrated by this organism differ from the resistance it typically shows to penicillin?
5. Why is vancomycin a good treatment choice when penicillin and methicillin are ineffective?
6. What complications are associated with IV vancomycin treatment?
7. Tony’s infection progressed rapidly and resulted in substantial soft tissue damage. Why is MRSA able to cause this problem?