Bacteria and Gram Stain

Topics: Bacteria, Gram staining, Microbiology Pages: 7 (1500 words) Published: December 8, 2011
Biochemical Unknown Report

A- Slant Culture


Diagnostic Key for A

Gram Positive Rods

B.subtilis C. xerosis

Starch Plate

+ - B.subtilis C.xerosis L.casei


+ -

L.casei B.subtilis

For my slant Culture A I first did a gram stain to figure out if it was positive or negative and to figure out if it was a rod or a cocci. I determined through my gram stain that it was a Gram positive rod. This narrowed it down to three bacteria. Using my diagnostic key I then first did the starch plate test. The starch plate test is a test that shows the absences of starch or the presence of starch around the bacteria on the starch plate. The results for the starch plate were negative there was no halo or clearing on the starch plate when I added the iodine to it. From my results of this test I believed my unknown bacteria for A was C.xerosis but I was not positive of this so I did the MR and VP test to make sure. “The MR test is designed to detect organisms capable of performing a mixed acid fermentation” ( Leboffe, Michael…,2008). The MR test gives you the results immediately after you put the tree drops of Methyl Red in it. If it turns red immediately then it is positive but if it has know color change then it is negative. My results for the MR test were negative. This means that my bacteria could be either C. xerosis or B.subtilis which was also negative in the starch plate test. I then did the VP test to see if it was B.subtilis or C.xerosis. The VP test has similar results readings like the MR test where if it turns red than it means it is positive but if there is no color change than it is negative; this test however is not immediate it takes 60 minutes. My results for the VP test were negative which means that my bacteria for the slant A bacteria is C. xerosis. The MR and VP test that I did were confirmatory test to make sure that my results for the starch plate test were accurate. All these test I did helped me in determining which bacteria I had.

The bacteria I identified Corynebacterium xerosis does have a health importance it “is an aggressive bacterial infection that may compromise organ function if left untreated. Generally affecting the mucous membranes, Corynebacterium xerosis may also present as a cutaneous infection causing localized irritation, inflammation and ulcer formation” (Willhite,2011). If it is not cured it can have “extensive and irreversible organ, respiratory and neurological damage may result” (Willhite,2011).

“Corynebacterium xerosis is no longer a prominent threat in Europe and the United States due to medical advances and the introduction of the diphtheria vaccination. Malnourishment and unsanitary conditions are considered contributory factors that increase one’s chances of contracting Corynebacterium xerosis in some areas. Individuals who travel to areas where diphtheria remains a risk are encouraged to make sure they have been fully immunized prior to traveling” (Willhite,2011). That is the medical importance of my bacteria C.xerosis.

B – bacteria from mixed broth culture


Gram + Cocci






+ -




+ - + -

Continue Reading

Please join StudyMode to read the full document

You May Also Find These Documents Helpful

  • gram stain Essay
  • Bacteria Classification by Gram Staining Essay
  • Staining: Bacteria and Stain Essay
  • Bacteria Essay
  • Differentiating Organisms Using a Gram Stain Essay
  • Gram Positive Bacteria & Antibiotic Resistance Essay
  • Gram Stain Lab Essay
  • lab for gram stain Essay

Become a StudyMode Member

Sign Up - It's Free