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Microbial Growth ch6

Prof. Khan chapter 6 notes

Microbial Growth What is Growth? (True) Growth is an increase in cell numbers. An increase in cell mass does not necessarily signify growth; it may be due to increase in the number of inclusion bodies.
Bacterial growth -by binary fission A. The parent cell enlarges. LAG phase B. Chromosome (DNA) duplicates. LAG phase C.A central transverse septum forms that divides the cell into 2 daughter cells. LOG Phase Some microorganisms grow by budding or fragmentation.(Fungi)
Generation Time: Generation Time: The time required for the cell population to double. E.coli:20 to 30 minutes. 1 Parent 2 First 4Second 8 Third 16 Fourth
Physical Requirements for Growth: 1 Temperature 2. pH 3. Osmotic pressure 4. Gas Requirments
Physical Requirements for Growth: TEMPERATURE A.Minimum growth temperature B.Optimum growth temperature- best growth C.Maximum growth temperature
Microorganisms can be classified into three major groups on the basis of temperature range. 1. Psychrophiles (cold-loving) 2. Mesophiles (moderate temp. loving – most human pathogens 3. Thermophiles (heat-loving)
Temperature range for bacterial growth Temperature (ºC) Min Opt Max Psychrophiles 0 15 20 Mesophiles 25 37 40 Thermophiles 40 50-60 85
Physical Requirements for growth - pH The degree of acidity or alkalinity of a solution. Or A measure of hydrogen ion concentration of a solution.
pH Acidophiles A. Acidophiles- Acid loving pH range: 1----------6.0 Example: a. Bacteria: Sulfolobus acidocaldarium(non-human pathogen) • Helicobacter pylori( human pathogen) b. Algae: Cyanidium caldarium and Most Fungi
pH Neutrophiles B. Neutrophiles – Most human pathogens pH range: 6.5 --------- 7.5 Examples: E. coli and S. aureus
pH Alkalophiles- bleach C. Alkalophiles PH range: 8.0 -------- 11.0 Example: Alcaligenes faecalis Bacillus alkalophile – Bleach
Buffer Any substance that prevents extreme pH changes Potassium Phosphate
Osmotic Pressure Osmophiles (halophiles and saccharophiles are organisms that can tolerate high solute concentration in their environment.
osmotic pressure - Facultative halophile Facultative halophile- Human pathogen Organisms that do not require high salt concentration but can tolerate it. Example: S. aureus (can grow in 7.5% salt solution)doesn’t require
osmotic pressure- Obligate Halophiles: Obligate Halophiles: Organism that require high salt concentration for growth. Example: Halobacterium salinarium requires at least 12% salt for growth.
Bacterial growth- Gas Requirments - Aerobes Mycobacteria, Legionella, and Pseudomonas species. Aerobes: Are growing in presence of oxygen (20.9%)They synthesize enzymes like catalase,superoxide dismutase, or peroxidase.These enzymes help eliminate toxic forms of O2 such as hydrogen peroxide,superoxied free radicals.Mycobacteria, Legionella pse
Gas Requirments - Facultative Anaerobes Facultative Anaerobes Prefer to grow in the presence of oxygen but can also grow in its absence. Examples: E. coli and S. aureus
Gas Requirments - Obligate Anaerobes Obligate Anaerobes Grow only in the absence of oxygen. Some may require 5-10% CO2 for growth. Example: Clostridium perfringens (caused gas gangrene) Clostridium Botulinum
Gas Requirments - Microaerophiles Microaerophiles Require low concentration (2-10%) of oxygen for growth. Enzymes are either absent or ineffective. Pathogens use host’s enzyme to eliminate toxic oxygen. Examples: T. pallidum- syphilis and Campylobacter jejuni
Anaerobic Growth Media and Methods 1. Reducing Media Example: Sodium Thioglycollate 2. The Anaerobic Jar (GasPak Jar) Sodium Bicarbonate + Sodium Borohydride + Water Hydrogen and Carbon Dioxide Gas + Oxygen Palladium Water
Chemical Requirements for Microbial Growth Macronutrients: Organic molecules such as amino acids and sugars that are required in large quantities for cell growth
Chemical Requirements for Microbial Growth- Micronutrients Nutrients like manganese, zinc, molybdenum, and vitamins that are needed in minute quantities for cell growth. Needed for synthesis of Holoenzymes .
Nutritional Patterns among Microbes: On the basis of energy and carbon source organisms can be classified into the following four categories: photoautotrophs, chemoautotrophs, photoheterotrophs and chemoheterotrophs
1-Photoautotrophs Organisms that obtain energy from light and use carbon dioxide as their major carbon source. Examples: Cyanobacteria, Algae, and Plants.
2-Chemoautotrophs Organisms that use inorganic compounds such as hydrogen sulfide(H2S),ammonia(NH3), elemental sulfur (S) etc. As their energy source and they use CO2 as their sole source of carbon Example: Thiobacillus thiooxidans& Thiobacillus ferrooxidans
3-Photoheterotrophs Organisms that use light as their energy source but cannot utilize CO2 as carbon source instead they use organic compounds such alcohols and sugars.non human pathogenic. Examples: Rhodopseudomonas palustris and Rhodospirillum rubrum
4-Chemoheterotrophs Organisms that use organic compounds as both energy and carbon source. Most are saprobes but some are parasites. Saprobe can grow without living host. Examples: Most bacteria and protozoans, all fungi, and animals.
Bacterial Culture Media Medium:Any substance (liquid or solid) which supports the growth of microorganisms.
Types of Media Synthetic of Chemically Defined A medium whose exact chemical composition is known. Poor nutrition value. Examples: (1) Inorganic synthetic broth – no growth (2) Glucose salt broth- yes used for research
Types of Media Non-synthetic or Empirical or Complex Media A medium that contains at least one ingredient of unknown composition. Complex media- nutritionally rich media .
Selective Medium Selective Medium: Allows the growth of certain type(s) of microbes while inhibiting the growth of other.Ex: 1.Sabouraud’s Agar (pH 5.6,for the isolation of fungi) 2.MacConkey(crystal violet, for isolation of Gram-negative bacteria)G+ no growth
Differential Medium Distinguishes between different types of micro-organisms through the physiological reactions unique to those microbes Examples: 1. Blood Agar (differentiates bacteria on the basis of hemolysis).
Blood agar hemolysis a. Beta hemolysis (clear zone around growth) Streptococcus pyogenes - complete b. Alpha hemolysis (greenish zone around growth) S.mitis - partial c. Gamma hemolysis (no zone around growth)E. faecalis feeds on plasma - no hemolysis
Mannitol Salt Agar 7.5 % Salt It differentiates between different types of staphylococci on the basis of mannitol fermentation. a.S. aureus ferments mannitol and changes the color of the medium from pink to yellow b. S. epidermidis unable to ferment mannitol. No change in color m
Bacterial Growth Curve Involves the following 4 major phases
LAG phase • Cells do not duplicate-DNA is duplicating and everything of the cell is duplicating. • Cells are metabolically very active • New cell components are synthesized • Injured/damaged cells repair themselves
LOG phase Cells divide at the maximum rate as long as environmental conditions are favorable.
Stationary phase Bacteria enter into this phase because: • Depletion of nutrients • Excretion of metabolic waste in the medium • Unavailability of oxygen or carbon dioxide • Increase in density of cells
d. Death Phase • Number of dead bacteria is greater than the number of viable bacteria • Time for death phase varies from bacteria to bacteria
Time for death 1 Mycoplasma – no cell wall 2. E. coli - cell wall but no capsule 3. K. pneumonia – capsule but no mycolic acid 4. M. laprae – mycolic acid but no endospore 5. B. subtilis – endospores producer
Measuring microbial growth Serial Dilution Method Advantages 1. Only viable cells are counted 2. Allows isolation of colonies Disadvantages 1. Too expensive 2. Requires overnight incubation
Direct Microscopic Count Advantage 1. Quick, no incubation required Disadvantages 1. Counts both viable and non-viable microbes 2. Motile microbes many be counted more than once. 3. Microbes growing in bunches may not be accurately counted.
Turbidity Measurements Spectrophotometer is used to observe turbidity (optical density) of a specimen. Advantage 1. Quick Disadvantages 1. Count includes both living and non-living microbes. 2. Cannot discriminate between microbes and other particles. 3. Expensive
Movement of Nutrients Across the Cell membrane I. Passive Processes A. Diffusion B. Osmosis C. Facilitated Diffusion Movement of molecules (like sugar and amino-acids) from a higher to a lower concentration through carrier proteins. No energy (ATP) required.
A. Diffusion B. Osmosis C. Facilitated Diffusion A. Diffusion –movement of molecules B.Osmosis-only water moves from higher to lower concentration thru selectively perm. Membrane C. Facilitated Diffusion- process in which molecules move from higher to lower concentration through CARRIER PROTEINS.
II. Active processes Active transport and Group translocation
Active Transport : A process in which molecules move form a lower to a higher concentration through carrier proteins. Energy (ATP) is required. Carrier is needed . NO change of molecule.
Group Translocation A process in which molecules move from a lower to a higher concentration through carrier proteins.Energy (ATP) is required. Transported molecules are chemically altered so it can be utilized immediately by the cell.Faster way to make energy.
Endocytosis (Bulk Transport): A process in which macromolecules enter a cell. If a solid material is involved, the process is called phagocytosis. If liquid or dissolved material, it is called pinocytosis.Cant be utilized by most bacteria because they cant change because of cell wall
How do bacteria and fungi transport large organic particles across the cell membrane? Extracellular Digestion- drulling of a cell
Test question: you have bot aerobic and anearobic media. Where will more culture grow? Aerobic. More ATP - bigger colony
Anaerobic fermentation -no oxygen -organic compound as H2 -No kreb cycle -No ETC all the tubes will make the same amount of ATP's .
Most human pathogens are : 1.Chemoheterotrops 2. Mesophiles 3. Neutrophiles 4. Facultative Osmophiles 5. Facultative Halophiles
Created by: rkasiejka