Bacillus cereus



By: Talia Meidan

Unknown Bacteria #10, after countless experiments, was found to be Bacillus cereus.

Gram Stain Results

B. cereusis a gram positive bacteria. This was identified by the color that the bacteria appeared under the microscope during the gram stain test. Gram positive means that the bacteria only had one cell wall layer. The bacteria absorbed the crystal violet stain, leaving the bacteria to appear purple.
b_cereus.jpeg
B. cereus - Crystal violet gram stain

Environment and Metabolism
B. cereus grows best in 37 degrees. It was tested in 25, 30, and 37 degrees Celsius temperatures. There was definite growth in all three nutrient agar dishes. However, the the bacteria grew the largest colony in the 37 degree Celsius temperature.

B. cereus is methyl red positive. This means that the bacteria consumed glucose and produced an acid waste. To identify this, we measured methyl red into a test tube with our bacteria and liquid. We then placed the test tube onto the vortex stirrer and observed the color of the liquid. If it turned red/pink, it would produce an acid waste product. If it turned orange/yellow, it would produce a neutral waste product.

B. cereus is a motile bacteria, defined as bacteria that can move using a variety of mechanisms. It was determined by stabbing aninoculating loop with the bacteria on it once into the MIO agar. If it became foggy, then it would be motile, if not, nonmotile.
motile.jpeg
On the left: Non motile; On the right: Motile


B. cereus displays complete hemolysis (digestion of the hemoglobin) when incubated on a sheep's blood agar plate. Complete digestion of the hemoglobin is defined as "beta" (alpha being 1 tertiary structure digested and gamma being no digestion of the hemoglobin).
hemolysis.jpeg
Alpha, Beta, and Gamma hemolysis


B. cereus, in classroom laboratory experiments was found to be facultative, meaning it can grow with or without oxygen. However in literature, B. cereus is classified to be strictly aerobic (only grows in oxygen).

Antibiotic Resistance

In the Baur-Kirby Test, Chloramphenicol, Streptomycin, Tetracycline, and ordinary hand sanitizer were tested to determine if they terminated B. cereus entirely. The hand sanitizer did minimal damage to the bacteria and would not be affective. Chloramphenicol, because it is a gorillacillin, worked best. The Streptomycin came next, then the Tetracycline. A doctor would typically prescribe Streptomycin to an ordinary patient with this bacteria. Chloramphenicol, the gorillacillin, would only be prescribed to the patient if their strain of the bacteria was too resistant to be killed off by Streptomycin.

Pathogenicity
B. cereus can be found in a few places in the environment. One is on insects, using their nutrients to survive. It is also commonly found in soil, or in the rhizosphere of some plants. Some symptoms of B. cereus poisoning are: food poisoning (vomiting, diarrhea), infections, blindness, lung problems, and viruses.

Sources:
http://microbewiki.kenyon.edu/index.php/Bacillus_cereus
http://inst.bact.wisc.edu/inst/index.php?module=book&func=displayarticle&art_id=118
http://micro-scopic.tumblr.com/post/5366940570/bacillus-cereus
http://www.bellarmine.edu/faculty/mlassiter/teaching.asp