Difference Between Gram Positive & Negative Bacteria

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  • 0:00 The Bacterial Cell Wall
  • 0:41 Identifying Bacteria
  • 2:04 Lesson Summary
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Lesson Transcript
Instructor: Gretchen Baumle
If you've ever had a bacterial infection, your doctor probably did a Gram stain to help figure out which kind of bacteria it is. This a common technique used by many labs and hospitals to identify and help combat a bacterial infection.

The Bacterial Cell Wall

Bacteria are clever little organisms that can employ an arsenal of tricks to evade their host's immune system. A large part of their success at infecting other organisms (humans included) involves the makeup of their cell wall. Bacteria are single-celled organisms that have either a thick or thin layer of a special material unique to bacteria called peptidoglycan, which surrounds a cell membrane composed of lipids (fats). Peptidoglycan is a key component of bacterial cell walls and is made of small protein and sugar pieces woven together like a basket.

Identifying Bacteria

Lab workers can apply certain dyes or stains to bacteria to identify an unknown invader. They'll typically apply several dyes in a process known as Gram staining, named after Hans Christian Gram, the scientist who discovered the identification technique. Both dark violet and bright red stains are applied during this process, and as a result the bacteria usually appear either bright pink or dark purple under a microscope.

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