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 2

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 4

Differential Media 5 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 – CO 2 – 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 (PO 4 )

Nitrogen Required for the synthesis of: –Amino acids –Nucleic acids –Peptidoglycan Sources: –Organic: Amino acids –Inorganic: NH 3, NO 3, & N 2

Sulfur Required for the synthesis: –Amino acids (Cysteine/Methionine) –Vitamins (thiamine and biotin) Sources: –Organic: Amino acids Cystein and methionine –Inorganic: S, SO 4

Hydrogen and Oxygen Required for the synthesis of organics!! –Carbohydrates –Lipids –Proteins –Nucleic acids Sources: –Organic: Organic carbon –Inorganic: H 2 (Methanogens only)

Nutritional Classification Carbon sources –Heterotrophs: Preformed organic compounds –Autotrophs: Inorganic molecules –CO 2 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 16

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 O 2 Anaerobic respiration uses an inorganic compound other than O 2 (Ex. NO3-) –End product H 2 O

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 (CO 2 ) –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…