Transcript Document
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 • Allows the discrimination of different species • Often contain pH indicators – Allows the discrimination of different metabolisms Production of alkaline products turns the medium red Production of acid products turns the medium yellow 5 Nutrition • Macronutrients – C,H,N,O,P,S Carbon • Required for the synthesis of all organic compounds : – – – – Carbohydrates Lipids Proteins Nucleic acids Carbon Sources • Organic – – – – – – – Monosaccharides Disaccharides Polysaccharides Proteins Lipids Nucleic acids Phenols, Etc. • Inorganic – CO2 – CO 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 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 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…