BIO 1
Section 3
Dr. Pablo Delis
Student Name
9/24/09
Microorganisms
In this lab, students will become more familiar with microorganisms and the
methods used for handling and observing them in the lab. Students will perform a Gram
stain, become familiar with sterile techniques for working with bacteria, recognize basic
bacterial forms and structures, and recognize basic protistan structures.
The lab starts by introducing students to some background information on Gram
staining. The Gram stain itself was developed in 1884 by Hans Christian Gram in
Germany. The stain is used to differentiate organisms based on their ability to retain a
certain staining compound. The technique separates bacteria into Gram-positive
(Gram+) or Gram-negative (Gram-) classifications. Gram staining can also be used in
medicinal applications as well.
After the background information on Gram staining, the lab goes into the
technique of Gram staining. The first step involves staining a fixed smear of organisms
with the primary stain of crystal violet. Next, you must apply Gram's iodine stain, which
is also called mordant. Mordant is a substance capable of intensifying the reaction of a
specimen to a stain. The next and most important step of Gram staining is to wash the
stained smear with a decolorizing agent. In most cases, 95% ethanol is used in this
step. Finally, you must counterstain the smear with safranin. Gram+ organisms will
