18.4 Bacteria and Archaea KEY CONCEPT Bacteria and archaea are both single-celled prokaryotes.
Introduction to bacteria. Key features of a bacteria.
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Transcript of Introduction to bacteria. Key features of a bacteria.
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