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

3

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…