Culture Media Preparation, Pure Culture techniqueUbiquity 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 properties1- are eukaryotes2- are non photosynthetic3- propagate by sporulation4- cell was is made up of chitin5- 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!