Chapter 6 Microbial Growth Lecture Outline PDF

Chapter 6 Microbial Growth 1 Microbial Growth How is microbial growth determined in the lab? Observation - of a culture medium  Ex - Nutrient Agar vs Nutrient Broth What do you look for? 2 Bacterial Growth and Colony Formation 3 Requirements for Microbial Growth Physical Requirements: Temperature...

Chapter 6 Microbial Growth 1 Microbial Growth How is microbial growth determined in the lab? Observation - of a culture medium  Ex - Nutrient Agar vs Nutrient Broth What do you look for? 2 Bacterial Growth and Colony Formation 3 Requirements for Microbial Growth Physical Requirements: Temperature pH of environment Osmotic pressure Chemical Requirements: Macronutrients Micronutrients Oxygen requirements 4 Temperature Minimum growth temperature Maximum growth temperature Optimum growth temperature 5 Temperature Preferences of Some Microbes Psychrophiles Mesophiles Thermophiles 6 pH of Environment Bacteria Molds and yeasts Acidophiles 7 Osmotic Pressure How does osmotic pressure effect microbial growth? If the osmotic pressure is not equal inside and outside the cell  cell will either shrink or swell  cell will die! Cell in an isotonic solution is ideal for survival Halophiles High osmotic pressure outside cell is produced by high salt environment; normally cell should shrink! Cells capable of producing positively-charged solutes inside  balance out osmotic pressure  cells survive! 8 Macronutrients Chemicals required by microbes in large quantities Microbes can use & metabolize different chemical elements Carbon Nitrogen Sulfur Phosphorus 9 Macronutrients - Carbon and Nitrogen Carbon Why do microbes need carbon?  To produce energy Where does the carbon come from? 1. From CO2 (for autotrophs)  energy! 2. From organic compounds (for heterotrophs)  energy! Nitrogen Which organic compounds have nitrogen?  Proteins  Nucleic acids 10 Macronutrients - Sulfur & Phosphorus Sulfur  What organic compounds have sulfur?  Proteins (2 sulfur-containing amino acids) Phosphorus  What organic compound has phosphorus?  Nucleic acids (nucleotides)  For cell membrane formation 11 Micronutrients AKA “trace elements” Chemicals required by microbes in small quantities Usually function as: Inorganic enzyme cofactors (Ex - iron, copper, zinc) Organic growth factors (vitamins A & D, animal extract in lab media) 12 Oxygen Requirements of Microbes 1. Obligate aerobes 2. Obligate anaerobes 3. Facultative anaerobes 4. Microaerophiles 13 Culture Media A solid or liquid preparation for microbial growth 1. Solid (agar) media - What can you see on nutrient agar? 2. Liquid (broth) media - What can you see in nutrient broth? Inoculum - introduction of microbes into a medium Culture - microbes growing in or on a culture medium Pure culture - contains only one species seen on solid agar plate Colony - population of cells from a single cell or from a group of attached cells A colony is often called a colony-forming unit (CFU) 14 Culture Media for Bacterial Growth Streak Plate Method - used to isolate pure bacterial cultures Figure 6.11 15 Culture Media for Viral Growth Virus requires a host cell (bacterial cell) Form a viral plaque Plaque-forming unit (PFU) 16 Types of Culture Media 1. Chemically defined media 2. Complex media 3. Reducing media 4. Selective media 5. Differential media 6. Enrichment media 17 Chemically Defined and Complex Media Chemically Defined Media Exact chemical composition is known Complex Media Chemical composition varies from batch to batch 18 Reducing Media All available O2 removed For growth of anaerobic bacteria Contain chemicals that combine with O2 to deplete it  Ex - Anaerobic Jar Figure 6.6 - Anaerobic Jar 19 Selective Media Suppress unwanted microbes and encourage growth of desired microbes  Ex - EMB (Eosin Methylene Blue) agar EMB Agar 20 Differential Media Allow differentiation between bacteria within same a group  Ex - Blood agar Some media have both selective and differential characteristics Blood Agar  Ex - EMB agar EMB Agar 21 Enrichment Media Considered a non-selective medium Stimulate growth of many different types of bacterial species Some fastidious bacteria (“picky/difficult eaters”) - require many growth factors Usually exist as liquid (nutrient broth) 22 The Growth of Bacterial Cultures Bacterial Division Increase in number of cells, not cell size Process called binary fission Generation Time Time required for a cell to divide (to double) Ranges - in minutes to hours Bacterial growth represented by growth curves 23 Bacterial Growth Curve Figure 6.15 24 Measurement of Microbial Growth: Direct Methods vs Indirect Methods Direct Measurements = counting  Plate count  Filtration method  Direct microscopic count Indirect Measurements = not counting  Turbidity  Metabolic Activity  Dry weight 25 Plate Counts Follows these steps: 1. Perform serial dilutions of sample 2. Plate out serial dilutions 3. Colony count Figure 6.16 26 Filtration Method Solution passed through a filter  collects bacteria Filter is transferred to a Petri dish  grows as colonies on the surface Figure 6.18 27 Direct Microscopic Count Volume of a bacterial suspension placed on a slide Average number of bacteria per viewing field is calculated Uses a special cell counter Figure 6.20 28 Indirect Methods Turbidity Observe liquid broth Measurement of cloudiness with a spectrophotometer Figure 6.21 29