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Bacteria Identification : Growth Parameters. Complex Media Made from complex and rich ingredients...
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Bacteria Identification :Growth Parameters
Complex Media
• Made from complex and rich ingredients– Ex. Soya protein extracts– Milk protein extracts– Blood products– Tomato juice, etc.
• Exact chemical composition unknown• Can be selective and/or differential
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Defined Media
• Known chemical composition– May contain up to 80 different ingredients– May be quite simple– Allows the growth of a restricted number of
microorganisms– Highly variable composition as a function of the
microorganism• May be selective and/or differential
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Selective Media
• Contains compounds which inhibit or kill the unwanted organisms– Ex. Medium containing penicillin only allows the
growth of penicillin resistant microorganisms
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Differential Media
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• Allows the discrimination of different species• Often contain pH indicators
– Allows the discrimination of different metabolisms
Production of acid products turns the medium yellow
Production of alkaline products turns the medium red
Nutrition
• Macronutrients – C,H,N,O,P,S
Carbon
• Required for the synthesis of all organic compounds :– Carbohydrates– Lipids– Proteins– Nucleic acids
• Organic– Monosaccharides– Disaccharides– Polysaccharides– Proteins– Lipids– Nucleic acids– Phenols, Etc.
• Inorganic– CO2
– CO
Carbon Sources
Phosphorous
• Required for the synthesis of :– Nucleic acids– Phospholipids– ATP – Used as a buffer; control of pH
• Sources: – Organic and inorganic
• The inorganic form is the most used (PO4)
Nitrogen
• Required for the synthesis of:– Amino acids– Nucleic acids– Peptidoglycan
• Sources: – Organic: Amino acids– Inorganic: NH3, NO3, & N2
Sulfur
• Required for the synthesis:– Amino acids (Cysteine/Methionine)– Vitamins (thiamine and biotin) • Sources: – Organic: Amino acids• Cystein and methionine– Inorganic: • S, SO4
Hydrogen and Oxygen
• Required for the synthesis of organics!!– Carbohydrates– Lipids– Proteins– Nucleic acids
• Sources: – Organic:
• Organic carbon– Inorganic:
• H2 (Methanogens only)
Nutritional Classification
• Carbon sources – Heterotrophs: • Preformed organic compounds– Autotrophs: • Inorganic molecules– CO2 and CO
Nutritional Classification (Cont’d)
• Energy sources– Phototrophs:
• Light– Chemotrophs:
• Oxidation of organic and inorganic compounds
• Source of e-– Organotrophs:
• Reduced organic molecules– Lithotrophs:
• Reduced inorganic molecules
Nutritional Types
• Autotrophs photolithotrophs• Heterotrophs photoorganotrophes• Autotrophs chemolithotrophs• Heterotrophs chemoorganotrophs
Environmental Parameters
• Oxygen availability• pH• Temperature
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Oxygen Requirements
• Aerobic:– Absolute need of oxygen to survive– Used as a final electron acceptor– Used by bacteria that carry out an oxidative or
aerobic respiratory metabolism• Microaerophilic:
– Absolute need for low concentrations of oxygen– High concentrations are detrimental
Oxygen Requirements (Cont’d)
• Anaerobic/Aerotolerant:– Oxygen is not required for growth or survival but is
tolerated• Facultative anaerobes:
– Facultative oxygen requirement– May use oxygen or not– Possesses an oxygen dependant and oxygen
independent metabolism• Strict or obligate anaerobic :
– Oxygen is neither used nor tolerated; cannot survive in the presence of oxygen
Bacterial Metabolism
• Most microorganisms initially channel the carbon source through a glycolytic pathway → pyruvate
• Different pathways are used to metabolize pyryvate– Respiration/Oxidation– Fermentation
Bacterial Metabolism (Cont’d)
• Respiration – Can occur aerobically or anaerobically– Both use an inorganic final electron acceptor
• Aerobic respiration uses O2
• Anaerobic respiration uses an inorganic compound other than O2 (Ex. NO3-)
– End product H2O
Bacterial Metabolism (Cont’d)
• Fermentation– Pyruvate is metabolized anaerobically– Makes use of an organic electron acceptor– Many diverse electron acceptors used by different
microorganisms• Different end products generated as a function of final
electron acceptor used– Very useful for microbial identification
Fermentations
• By-products: – Most generate acid + gas (CO2)– A few generate only acid or gas
Parameters Used in Bacterial Identification
-Presence of exocellular enzymes-α-amylase, etc…
-Oxygen utilisations (Anearobic vs. Aerobic)-Slants, etc…
-Anaerobic respiration products-Nitrate Reductase, etc…
-Fermentation Products-ethanol, etc…
-Survival on a selective media-survives in presence of an antibiotic, etc…