Introduction to bacteria

Key features of a bacteria

Identifying bacteria Size, shape, color Culturing techniques Metabolic attributes DNA

Gram stain Usually the first test done to identify bacteria The Gram's stain differentiates between two major cell wall types. Gram positive and Gram negative

Gram positive Gram positive bacteria have walls containing relatively large amounts of peptidoglycan = a starch Staphylococcus epidermidis, Streptococcus pyogenes, Clostridium tetani, Bacillus anthacis (ANTHRAX)

Gram negative Gram negative species have walls containing small amounts of peptidoglycan and a lipopolysaccharide = a fat/sugar combo Escherichia coli, Salmonella typhi, Vibrio cholerae and Bordetella Gram negative bacteria are harder to control with antibiotics

Exceptions Not all bacteria can be stained by Gram's method the best-known exceptions belong to the genus Mycobacterium which have waxy cell wall. These include Mycobacterium tuberculosis (TB) and Mycobacterium leprae (leprosy).

Gram stain has four steps: 1. crystal violet, the primary stain 2 Gram stain has four steps: 1. crystal violet, the primary stain 2. iodine, which acts as a mordant by forming a crystal violet-iodine complex 3. alcohol, which decolorizes 4. safranin, the counterstain. G+ organisms are purple (or bluish), G- organisms are red.

How does it work?

Cell envelope of Gram positive

Cell envelope of Gram negative

Summary Know how bacteria are different than eukaryotic cells Know key features of bacteria Know a key difference between Gram + and Gram - bacteria Know how the gram stain works and how we use it