BIO 214-MRSA Case Study modified (1)

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Apr 3, 2024

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Microbiology Bio 214 Case Study MRSA Case Study Part I – Measuring Resistance Katelyn was excited to start her summer job in her microbiology professor’s research laboratory. She had enjoyed Dr. Johnson’s class, and when she saw the flyer recruiting undergraduate lab assistants for the summer, she had jumped at the opportunity. She was looking forward to making new discoveries in the lab. On her first day, she was supposed to meet with Dr. Johnson to talk about what she would be doing. She knew the lab focused on antibiotic resistance in Staphylococcus aureus especially MRSA (methicillin-resistant S. aureus). She still remembered the scare her family had last year when her little brother, Jimmy, got so sick. He had been playing in the neighborhood playground and cut his lip when he fell off the jungle gym. Of course, he always had cuts and scrapes—he was a five-year-old boy! This time though his lip swelled up and he developed a fever. When her mother took him to the doctor, the pediatrician said the cut was infected and had prescribed cephalothin, an antibiotic related to penicillin, and recommended flushing the cut regularly to help clear up the infection. Two days later, Jimmy was in the hospital with a fever of 103°F, coughing up blood and having trouble breathing. The emergency room doctors told the family that Jimmy had developed pneumonia. They started him on IV antibiotics, including ceftriaxone and nafcillin, both also relatives of penicillin. It was lucky for Jimmy that one of the doctors decided to check for MRSA, because that is what it was! MRSA is resistant to most of the penicillin derivatives. Most cases of MRSA are hospital- acquired from patients who are already susceptible to infection, but the ER doctor explained that community-acquired MRSA was becoming more common. The doctor then switched the treatment to vancomycin, a completely different kind of antibiotic, and Jimmy got better quickly after that. Katelyn had dropped Jimmy off at swimming lessons just before coming to work at the lab. As she waited in the hallway for Dr. Johnson, she hoped that she would be at least a small part of helping other people like Jimmy deal with these scary resistant microbes. She was surprised when the professor burst out of the lab, almost running into her. “Hi Katelyn, I’m really sorry but I have to run to a meeting right now—they sprung it on me last minute. There are bunches of plates in the incubator right now that need their zones of inhibition measured. I’ll be back in a few hours,” Dr. Johnson said as he rushed down the hallway with a stack of folders. Katelyn dug out her old lab notebook to look up what she was supposed to do. She found the lab where she and her fellow students had examined the antimicrobial properties of antibiotics using the Kirby-Bauer disk diffusion technique. Looking at

Microbiology Bio 214 Case Study the plates Dr. Johnson had told her about, she saw they had all been “lawned,” or completely coated with microbes to make a thick hazy layer over the agar surface. She could also see paper disks with letters on them, and some of the disks had clear zones around them where the microbe had been inhibited (Fig. 1). Her notebook explained how to measure the zone of inhibition around the disks (Fig. 2).

Microbiology Bio 214 Case Study Plate 1. Plate 2. Plate 3. S. aureus PE CE ME VA S. aureus PE CE ME VA S. aureus PE CE ME VA PE CE ME MRSA VA PE CE ME MRSA VA PE CE ME MRSA VA

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