Transcript Introduction to bacteria - College Heights Secondary

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