Measuring Resistance Katelyn was excited to start her summer job


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BIO 127 QEP (1).docx 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). 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’s 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 a bunch 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 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). Figure 1. Agar plates of S. aureus or MRSA lawns with antibiotic disks placed on them. Figure 2. Katelyn’s diagram of how to measure a zone of inhibition from her microbiology lab notebook. Question 1 (10 points) Measure the zones of inhibition for each antibiotic on the plates shown in Figure the measurements in the spaces in Table 1 below. (Note: The Kirby-Bauer standardized so that no zone of inhibition is scored as a 0, and all others include part of the zone.) Key: PE = penicillin, ME = methicillin, CE = cephalothin, vancomycin Plate 1 2 3 S. aureus 1 and note method is the disk as and VA = MRSA PE ME CE VA PE ME CE VA PE ME CE VA Question 2 (10 points) In Table 2 below calculate and record the averages and standard errors for each antibiotic in S. aureus and MRSA. 1. Average = Sum of the values for each antibiotic/ total number of times recordings taken (A+B+C)/3 see table 1. 2. Please use excel or scientific calculators to measure the Standard deviation. 3. Standard Error = SD/√n S. aureus Average MRSA SE Average SE PE ME CE VA Question 3 (10 points) Now, redraw Tables 1 and 2 into a single, more organized table. Be sure to label the table appropriately. Question 4 (5 points) Graph the results from Ta

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