Microbial Growth • Physical Requirements of Microbes • Temperature (optimal enzyme operation) • Psychrophiles, mesophiles, thermophiles • pH (optimal enzyme operation) • Using buffers in media • Molds & yeasts versus bacteria • Chemical Requirements • Carbon source in medium • Nitrogen, sulfur, phosphorous, trace elements • Oxygen requirements • Obligate aerobes, anaerobes, facultative anaerobes • Free radical oxygen (O 2 - ) and H 2 O 2 dangers; superoxide dismutase and catalase = aerobes • Culture Media for Microbes • Chemically defined vs. complex media • Anaerobes: reducing media/Brewer jar • Other: animals, eggs, tissue culture, CO 2 • Media types • Selective, Differential, Enrichment • Bacterial Population Growth • Growth Curve: Lag, Log, Stationary, Death • Quantifying Growth
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Microbial Growth Physical Requirements of Microbes Temperature (optimal enzyme operation) Psychrophiles, mesophiles, thermophiles pH (optimal enzyme operation)
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Microbial Growth• Physical Requirements of Microbes
• Free radical oxygen (O2-) and H2O2 dangers; superoxide dismutase and catalase = aerobes
• Culture Media for Microbes• Chemically defined vs. complex media
• Anaerobes: reducing media/Brewer jar
• Other: animals, eggs, tissue culture, CO2
• Media types
• Selective, Differential, Enrichment
• Bacterial Population Growth• Growth Curve: Lag, Log, Stationary, Death
• Quantifying Growth
• Goal: To chemically (or physically) suppress unwanted microbes and encourage desired microbes.
Selective Media
Figure 6.9b, c
Mannitol salt agar : selective for halophiles with 7% salt (osmotic challenge) and differential for mannitol fermenters: good for skin bacterial cultures.
EMB Agar: kills gram positives with eosin and methylene blue, selective for gram negatives. Differential for lactose fermenters. Good for growing enterics.
McConkey Agar: supresses gram positives with crystal violet and bile salts; also differential for
MSA
EMB
MA
• Distinguish between different species based on a metabolic ability.
Differential Media
Figure 6.9a
Blood agar(sheep’s blood) reveals if hemolytic
Mannitol salt agar contains the pH sensitive dye phenol red (yellow when acidic)
Se Sa
• Encourages growth of desired microbe by providing special growth conditions or added growth factors
Enrichment Media
Thioglycollate
Anaerobic or Brewer Jar
Glucose Salts Agar (enriches for microbes that can growth
only on glucose and some inorganic nutrients
Lysed red blood cells provide unique nutrients in
blood/chocolate agar
• A pure culture contains only one species or strain
• A colony is a population of cells arising from a single cell or spore or from a group of attached cells
• A colony is often called a colony-forming unit (CFU)
Pure Cultures Used To Study Characteristics Of A Particular Species
Microbial Growth• Physical Requirements of Microbes