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Transcript
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. 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