Bacterial Size and Oxygen Requirements

Study Notes

Obligate Aerobes: Need oxygen to survive; grow where high oxygen concentrations are present. Enzymes catalase and superoxide dismutase neutralize toxic oxygen forms.
Facultative Anaerobes: Can grow with or without oxygen, but grow best with oxygen; can utilize oxygen if it's available but can also grow in the absence of oxygen.
Obligate Anaerobes: Can't tolerate oxygen and grow only where oxygen is absent. Unable to neutralize toxic oxygen forms.
Aerotolerant Anaerobes: Grow in the presence of oxygen but are not harmed by it. They grow evenly throughout a tube.
Microaerophiles: Need low oxygen concentrations to grow. Toxic forms of oxygen are lethal at normal atmospheric levels.

Reducing media: Designed to grow obligate anaerobes by chemically removing oxygen.
Selective media: Designed to favor the growth of certain microbes while suppressing others.
Differential media: Allow for distinguishing different bacterial colonies based on differences in their metabolic activities.

Cell wall: Complex structure determining cell shape and preventing rupture.
Gram-positive bacteria: Contain many layers of peptidoglycan.
Gram-negative bacteria: Have one or fewer layers of peptidoglycan and an outer membrane.
Crystal Violet: Primary stain that stains both types purple.
Iodine: Mordant that forms a crystal violet-iodine complex.
Alcohol: Decolorizing agent; removes the crystal violet complex from gram-negative cells, leaving them colorless.
Safranin: Counterstain, staining gram-negative cells pink. Gram-positive cells are still purple from the initial stain, making the Gram-negative easier to distinguish.