Bacillus cereus & Proteus
mirabilis
Number 14
11/9/2011
Bio 303
Jourdan Beasley
2
Tests Used For Gram Negative:
Gram Stain: Red Rods
Oxidase Test: (-)
Urea Hydrolysis: (+)
H2S Production: (+)
Capsules: (+)
Motility: (+)
Tests Used for Gram Positive:
Gram Stain: Purple Rods
Vogues Pasteur: (-)
Catalase: (+)
Indole: (-)
Citrate: (+)
Spores: (+)
3
When I received my test tube full of two different bacteria, the first thing that I did was
plate my bacteria on an EMB and an MSA plate and I let them grow. I then did three gram
stains, one from my tube, one from my EMB plate and one from my MSA plate. I did this just so
I could ensure what I was seeing was correct. On my gram stains I discovered that I had a gram
negative rod and a gram positive rod.
With my gram positives I was able to eliminate M. leuteus, S. aureus and S. epidermis
which left me with B. subtilis, B. cereus and B. megaterium as possibilities for my unknown. I
first did my Vogues Pasteur test and that came out negative, this eliminated B. megaterium,
leaving my bacteria to be either B. subtilis or B. cereus. I then conducted a citrate, spore, indole
and catalase test to determine if my unknown bacterium was B.subtilis or B. cereus. My citrate,
spore and catalase tests all came out negative and my indole test came out negative. After
conducting some research, this was enough evidence to me that my gram positive bacterium is B.
cereus.
I then began to work on my gram negative bacteria. After my gram stain I performed an
oxidase test. This test came out negative with eliminated P. aurginosa and A. facealis from my
list of possible unknowns. This left me with the possibility of having E.coli, P. mirabilis, S.
typhimunum, E. aerogens, S. flexneri, K. pnemoniae or S. marcescens. I then performed my urea
hydrolysis test with came out positive. This eliminated all bacterium except for K. pnemoniae or
P. mirabilis. I then performed an H2S production test that came out positive therefore, telling me
that my unknown bacterium was P. mirabilis. I also performed a motility and capsule and both
came out positive. After conducting research I found that P. mirabilis had a capsule and was
motile, which proved my unknown gram negative bacteria.
4
Proteus mirabilis was first discovered by Gustav Hauser in 1978. This bacterium was
named after a character in The Odyssey. P. Mirabilis is a gram-negative bacterium. This
bacterium is rod shaped and is gram negative. P. Mirabilis can be considered a free-living
microbe. It can be found in the soil, in the water, and in humans urinary or gastrointestinal tract.
P. mirabilis is not usually considered pathogenic but it can become pathogenic. In order
for P. mirabilis to become pathogenic, it must come into contact with urea. The bacteria then
colonize in the urinary tract of the gastrointestinal tract. In order to keep growing and to cause an
infection, the bacterium must successfully fend off the defenses of the host. Their capsules help
them fight off the defenses in the host organism. Once the infection starts, it can spread to other
organs in the area of the gastrointestinal tract. P. mirabilis produces the enzyme urease. Since, it
produces the enzyme, it converts urea into ammonia. This infection can be detected by an
alkaline urine sample, which checks one’s urine for alkaline.
Current research shows that P. mirabilis, makes several different fimbriae that promote
adhesion to mucosal surfaces. Fimbriae are a series of threads or other projections that are used
for virulence. Virulence is a degree of pathogenicity of a bacterium. One of the fimbriae is
called the mannose resistant proteus-like fimbriae. This fimbriae is one that has a higher
presence in patients that are associated with urinary tract infections in humans. There is a
mannose resistant proteus-like gene (mrpH) that is present in the mrp operon of the mrp fibrae
that is essential for the functionality of adhesion. Researchers have used insertional mutagenesis
to find that without that functional gene there is less mr/p fimbriation. This concluded that the
capabilities of the mrpH gene can possibly lead to a vaccine to prevent P. Mirabilis from
attaching to the mucosal surfaces which will stop the infection altogether.
5
Bacillus cereus is a gram positive bacterium. It is a gram positive meaning that is has a
thinner peptide-glycan layer. It is normally 1X3-4μm. It can be easily mixed up with Bacillus
subtilis because of the size difference. This bacterium was first isolated in 1969 from a fatal case
of pneumonia in a male patient. The bacterium was cultured from blood and pleural fluid from
the patient. A comparison in RNA showed that B.cereus is closely related to Bacillus anthracis
and Bacillus thuringiensis. B. Anthracis is the cause of anthrax and B. thuringiensis is and
insect pathogen used in pesticides.
B. cereus is the most motiles out of the genus Bacillus. This bacterium is a mesophilic
meaning that it likes to grow at ranging temperatures from 20̊ C to 40̊ C. Bacillus cereus is
capable of adapting to a big range of environmental conditions. It is commonly found in soil and
in saprophytic organisms. Saprophytic organisms are organisms that feed on dead organic matter
such as fungi or bacteria. Bacillus cereus can also be found in the microflora of insects. It takes the
nutrients from the host to survive. It can also be found in the rhizosphere of some plants.
Since B.cereus is a soil bacterium, it can spread to different foods. Some foods that it can spread
to are plants, eggs, meat and dairy products. This bacterium is the cause of about 25% of food-borne
intoxications. This is due to the emission of emetic toxins (a toxin that causes puking) and enterotoxins.
Bacillus cereus is considered an opportunistic human pathogen. It can be associated with infections
occasionally. This bacterium is known to cause periodontal diseases and other more serious infections.
Those who are immunocompromised are susceptible to bacteremia, endocarditis, meningitis
pneumonia and endophthalmitis because of the bacteria Bacillus cereus. Sequencing the genome is vital
to expand knowledge for treatments and antimicrobial drugs.
The current research involved with Bacillus cereus deals with the ability of the bacteria to form
biofilms on surfaces that can cause potential contamination problems in the food industry.
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Works Cited
"Bacillus Cereus." MicrobeWiki. 22 Apr. 2011. Web. 08 Nov. 2011.
<http://microbewiki.kenyon.edu/index.php/Bacillus_cereus>.
"BioMed HTC - Proteus Mirabilis." BioMed HTC | Homepage. 22 Apr. 2011. Web. 08 Nov. 2011.
<http://www.biomedhtc.org.uk/ProteusMirabilis.htm>.
"Proteus Mirabilis." MicrobeWiki. 26 Aug. 2011. Web. 08 Nov. 2011.
<http://microbewiki.kenyon.edu/index.php/P._mirabilis>.