Campbell Biology 11th Edition by Lisa Urry,Michael Cain,Steven Wasserman,Peter Minorsky,Jane Reece

Exercise 5

Can a skin wound turn deadly
"That scrape I got at the game last week looks infected. I wonder if I should go to the doctor " Contact sports can be hard on your body even if you are in top physical condition. "Contact" in many cases leads to skin wounds that can become infected-and even deadly, if infected with antibiotic-resistant bacteria.
Watch the video in the Mastering-Biology Study Area to see what happened when a strain of antibiotic-resistant bacteria called MrSA infected at least one high school student. MrSA stands for methicillin-resistant Staphylococcus aureus , a strain of bacteria that is resistant to several types of antibiotics, not just methicillin. Most "staph" infections are not antibiotic-resistant and can be treated with antibiotics.
ABC news video: MRSA Outbreak
Staphylococcus aureus (S. aureus) is a common bacterial species found on the surface of healthy skin that can turn into a serious pathogen if introduced into tissue through a cut or abrasion. Once inside the body, a population of S. aureus that reaches a certain density will start to secrete a toxin, killing body cells and contributing significantly to inflammation and damage. Because about 1 in 100 people carry a strain of S. aureus that is resistant to common antibiotics, a minor infection can turn permanently harmful or even deadly.
In this exercise, you will investigate the mechanism by which cells sense their own population density (so-called quorum sensing ) to analyze whether blocking it can stop S. aureus from producing toxin.
Your Approach
The facts you have in hand for your investigation are that quorum sensing in S. aureus involves two separate signal transduction pathways that can lead to toxin production. Two candidate synthetic peptides (short proteins), called peptides 1 and 2, have been proposed to interfere with the S. aureus quorum-sensing pathways. Your job is to test these two potential inhibitors of quorum sensing to see if they block either or both of the pathways that lead to toxin production.
For your experiment, you grow four cultures of S. aureus to a standardized high density and measure the concentration of toxin in the culture. The control culture contains no peptide. The other cultures have one or both candidate inhibitory peptides mixed into the growth medium before starting the cultures.
Your Data
Data from N. Balaban et al., Treatment of Staphylococcus aureus biofilm infection by the quorum-sensing inhibitor RIP, Antimicrobial Agents and Chemotherapy 51(6):2226-2229 (2007).
Was there an additive effect on toxin production when peptides 1 and 2 were both present in the growth medium What is your evidence for this
Instructors : A version of this problem-Solving exercise can be assigned in MasteringBiology. Or a more extensive investigation called "Solve it: is it possible to treat Bacterial infections Without traditional Antibiotics " can be assigned.