From the Colorado Integrated Food Safety
Center of Excellence In the Lab Understanding basic techniques performed
at a public health laboratory. How is a gram stain performed on an
enteric pathogen? The laboratorian starts by fixing the bacteria to the microscope slide. To do this, the laboratorian takes colonies from a
blood agar plate and mixes it with saline on the slide. The slide is left to dry
for 10 to 15 minutes. Now the staining process begins. First, the laboratorian floods the slide with crystal violet. After 30 seconds, the slide is washed
under distilled water. Gram’s iodine comes next. After 30 seconds the slide is washed Next, decolorizer is dripped over the
slide until the runoff appears clear, followed by another quick
water rinse. Last, safranin stain is added and left
for thirty seconds then washed off the slide. The laboratorian will then view the
slide under the microscope and classify their bacteria as either gram-positive or gram negative.

In the Lab: Gram Stain Proccess
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