Ubiquity of Microorganisms

 A collection of a single type of bacteria isolated and growing free from all other microbes. Mixed CulturePure Culture

 When a single bacterial cell is deposited on the surface of a nutritive medium, it begins to divide.  After thousands (up to billions) of cells are formed, a visible mass appears.  This mass is called a colony.  Each species of bacteria and fungi exhibit a characteristic colony.

 1- Size: ◦ Can be reported in millimeters. ◦ Or, it can be reported as:  Pinpoint (tiny small colonies).  Small.  Medium size.  Large.

 2- Elevation: ◦ The appearance of colonies when viewed from the side. ◦ Colonies are described as:  Flat.  Raised.  Convex.  Umbonate.  Crateriform.

 3- Edge or Margin: ◦ The margin of a colony can be described as:  Entire.  Lobate.  Curled.  Undolate.  Or filiform.

 4- Whole colony shape (form): ◦ Colonies can be described as one of the following:  Filamentous.  Irregular.  Circular (round).  Rhizoid.

 5- Texture:  Moist, Mucoid or Dry (Rough).  6- Pigmentation: ◦ Color of bacteria (may change when the medium is changed).  7- Appearance: ◦ Opaque Vs Translucent. ◦ Shiny Vs Dull.  8- Odor: ◦ Listed only if distinctive (Sweet, putrefied or fruity). ◦ Example:  Pseudomonas aeroginosa smells like grapes.

 According to Oxygen requirements Tube (1): Obligate aerobic bacteria gather at the top of the test tube in order to absorb maximal amount of oxygen Tube (2): Obligate anaerobic bacteria gather at the bottom to avoid oxygen Tube (3): Facultative bacteria gather mostly at the top, since aerobic respiration is advantageous (ie, energetically favorable); but as lack of oxygen does not hurt them, they can be found all along the test tube Tube (4): Microaerophiles gather at the upper part of the test tube but not at the top. They require oxygen, but at a lower concentration Tube (5): Aerotolerant bacteria are not affected at all by oxygen, and they are evenly spread along the test tube

 According to turbidity:  Tube (1): uninoculated.  Tube (2): Motile bacteria (Uniform cloudiness).  Tube (3): bacteria tend to stick together in clumps (Flocculent growth).  Tube (4): Non-motile bacteria with waxy cell walls tend to float at the surface of the broth (Pellicle).  Tube (5): non-motile bacteria sink to the bottom of the tube (Sediment).