i am doing BI203 and i have to find the \"unknown\" for my lab by working on the

Question

i am doing BI203 and i have to find the "unknown" for my lab by working on the nameless broth (w/o genes and specific epithet). so far i haven't had any luck with the gram staining. the only clues i can give is the its purple for gram-stain so i can conclude that its gram positive and that the nutrient liquid cultue broth is pellicle i.e. thin whitish layer on the surface of the broth. any ideas on what it can be? or what are the microorganisms that form pellicle? one of the given following organisms can be mine, either staphlylococcus aureus, streptococcus pyogenes, micrococcus luteus, bacillus subtilis, lactobacillus lactis, enterobacter aerogenes, mycobacterium phlei, neisseria sicca, escherichia coli or proteus vulgaris.
with the above clues, can someone narrow down as to which of the following can be my microorganism for unknow? it will really help make my work easier. will rate earnestly.

Explanation / Answer

A lot of different microorganisms form pellicles, the most common being the ones on your teeth. Given what you have so far, you should start by crossing out all the gram-negative bacteria in that list. To identify your unknown, you're going to have to do some more tests; this isn't enough information so far. Some things to think about: What is its shape under the microscope (is it grape-like? is rod-shaped?)? Streptococcus, for instance, is round. E. Coli is rod-shaped. Can you test for antibiotic resistance/susceptability? Can you test survivability on nutrient-specific agar plates? These will help you narrow down the possibilities.

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