Transcript Culture Media Preparation, Pure Culture technique

Culture Media Preparation, Pure Culture technique
Ubiquity of Bacteria
The Fungi
Lab #5
Medgar Evers College
Bio 261, Microbiology
Prof. Santos
Exercise 7; The ubiquity of Bacteria
• Bacteria are found everywhere in this planet. They are uni-cellular
prokaryotic organisms capable of surviving even in the harshest
environments.
• The have a cell wall composed of peptidoglycan that differentiates
them into gram – and gram + bacteria depending on the biochemistry
of the cell wall.
• Bacteria can have three basic shapes; rod, sphere, or spiral.
Motility Mode
Bacilli- can be motile or non-motile depending on the presence of a
flagellum
Cocci- tend to be non-motile
Spirochaetes- motile due to the presence of an axial filament, a special
type of flagellum that originates from both ends of the cell and wraps
around the cell body.
• In this exercise, you will be given liquid broth and solid agar to inoculate or
expose to bacteria.
• With the cotton swab, rub a surface that you think has a high concentration of
bacteria such as a cell phone, doorknob, or tip of your shoes.
Exercise 8; Fungi
• Basic properties
1- are eukaryotes
2- are non photosynthetic
3- propagate by sporulation
4- cell was is made up of chitin
5- lack tissue differentiation
Molds
• Have microscopic intertwining filaments called Hyphae.
• A mass of hyphae is called a mycelium
• The hyphae can have cross walls called septa that separate the
hyphae into individual compartments.
• A special selective medium such as Sabouraud’s agar is used to
inhibit bacteria due to its acidic nature. Sometimes specific
antibiotics are added to the medium. Main components are
peptone and glucose.
Exercise 10; Pure culture technique
• Pure culture- a culture containing only 1 type of bacteria
• 2 methods used to obtain a pure culture are streak plate method and
the pour plate method.
• Both methods aim at diluting the original culture and obtaining a
single pure colony consisting of only 1 type of bacteria.
Aim
• You will be given a mixed culture of Micrococcus luteum, Serratia
marcescens, and Escherichia coli. You will use the streak plate method
to isolate the individual colonies.
• I will demonstrate!
Exercise 19; Culture media preparation
• Know the difference between complex and defined media.
• Complex media contains a variety of compounds needed by the
organism to grow but the exact composition is not known.
• In a defined medium, we know exactly what is in it. They are useful in
cultivating very fastidious organisms with strict requirements.
*7 requirements for any medium that is
prepared!
• Carbon source
• Energy source
• Water
• Minerals
• Vitamins
• Nitrogen
• Growth factors
Carbon source
• Depending on how an organism acquires its carbon, it is classified as
either an autotroph or heterotroph.
• Heterotrophs acquire carbon from organic matter such as
carbohydrates
• Autotrophs acquire carbon from fixing carbon dioxide.
Energy source
• Chemoorganotrophs- derive energy from the breakdown of organic
molecules by respiration or fermentation.
• Chemolithotrophs- oxidize inorganic ions such as nitrate or Iron to obtain
energy. Examples are nitrifying and Iron bacteria.
• Photoautotrophs- contain pigments such as chlorophyll to capture energy
from the sun and convert it to chemical energy stored in sugars. No energy
source is supplied in medium since the energy is supplied in the form of
light. Examples are purple sulfur bacteria and cyanobacteria.
• Photoheterotrophs- these organisms derive energy from the sun but their
carbon source is derived from organic molecules such a glutamate or
succinate. Example is the purple nonsulfur bacteria.
Other requirements
• nitrogen source (proteins)
• Minerals
• Vitamins
• growth factors
• water
• Please know that a selective medium allows one type of organism to
grow and inhibit others. Example EMB medium. This allows gram –
bacteria to grow and inhibits gram +.
• A differential medium allows a certain type of bacterium to take on an
appearance that distinguishes it from others. For example, S. aureus
when grown on Mannitol salt agar will produce yellow colonies since
they ferment the sugar mannitol to cause a change in pH. The phenol
indicator changes from red to yellow due to the acid formation.
• Know that media can be liquid (broth) or solid (agar) or some like SIM
medium can be semi solid to detect motility!