An 18 year old, previously healthy female presents to the student health service with fever, vomiting, and diarrhea. On physical examination, she is hypotensive and has an erythematous, red, sunburn-like skin rash. She is currently menstruating, and has been using super absorbent tampons. Which of the following findings from a positive blood culture would confirm your suspected diagnosis?

This is a multi-step microbiology question that requires you to diagnose the illness, identify the microorganism, and remember its key feature. The first pa should be easy: everything about this vignette suggests toxic shock syndrome. The organism in question is therefore Staphylococcus aureus, which is coagulase positive. All of the other choices are classic features of other impoant pathogenic microorganisms: Acid-fast organisms, refers to Mycobacteria. (In addition, Nocardia species are paially acid fast). EMB agar refers to a selective and differential medium used to isolate and identify enteric gram-negative bacteria. Gram-positive bacteria will not grow on EMB agar because the addition of eosin inhibits their growth. Non Lactose fermenters will have colorless colonies, while fermentation of this sugar will cause the colonies to appear pink or purple. Thayer-Main media is a growth medium for pathogenic Neisseria species. It contains the antibiotic vancomycin, which kills gram-positive organisms such as Staphylococcus aureus. Ref: Ray C.G., Ryan K.J. (2010). Chapter 24. Staphylococci. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.