Microbial Nutrition Lecture Notes

MICROBIAL NUTRITION Microorganisms require specific nutrients that are essential for their growth and multiplication. Elements such as oxygen, carbon, hydrogen, nitrogen, and sulfur are some of the needed substances in energy production and biosynthesis. Moreover, temperature, pH, and mois...

MICROBIAL NUTRITION Microorganisms require specific nutrients that are essential for their growth and multiplication. Elements such as oxygen, carbon, hydrogen, nitrogen, and sulfur are some of the needed substances in energy production and biosynthesis. Moreover, temperature, pH, and moisture are also necessary to facilitate their growth and survival. I. PHYSIOLOGIC REQUIREMENTS OF BACTERIA ACCORDING TO OXYGEN REQUIREMENT 1. Aerobes These organisms require oxygen and grow well with room air. Air contains 15% to 21 % oxygen and 1 % CO2 Examples: Bordetella, Brucella, Mycobacteria, and Pseudomonas ACCORDING TO OXYGEN REQUIREMENT 2. Anaerobes They do not require oxygen to grow and survive. Types of Anaerobes a. Obligate anaerobes They do not require the presence of oxygen, and they die after prolonged exposure to air. Examples: Clostridium and Bacteroides ACCORDING TO OXYGEN REQUIREMENT b. Facultative anaerobes They are the most clinically significant bacteria. These organisms grow either in the presence or absence of oxygen; hence they are considered as "aerobes that can grow anaerobically". They do not require oxygen but grow better in its presence. Example: Enterobacteriaceae c. Aerotolerant anaerobes These organisms can survive in the presence of oxygen but unable to perform metabolic processes unless situated in an anaerobic environment Example: Lactobacillus and Cutibacterium ACCORDING TO OXYGEN REQUIREMENT 3. Microaerophile It is an organism that requires only 2% to 10% oxygen for growth. Example: Campylobacter, Helicobacter, and Treponema NOTE Obligate aerobes and facultative anaerobes contain protective enzymes (superoxide dismutase and catalase) that counter the toxic effects of oxygen. ACCORDING TO CARBON DIOXIDE REQUIREMENT 1. Capnophiles require an increased CO2 (5% to 10% CO2). Most aerobic and facultative aerobic bacteria need 0.03% CO2 Example: Haemophilus influenzae, Neisseria gonorrhoeae, and Streptococcus pneumoniae ACCORDING TO NUTRITIONAL REQUIREMENT 1. As to the carbon source Autotrophs use carbon dioxide as the sole source of carbon. Heterotrophs utilize reduced, preformed, organic molecules from other bacteria. 2. As to the energy source Phototrophs are organisms that use light as their energy source. Chemotrophs make use of the energy produced by the oxidation of organic or inorganic compounds. ACCORDING TO NUTRITIONAL REQUIREMENT 3. As to the electron source Lithotrophs reduce inorganic molecules to be used in biosynthesis or energy conservation. Organotrophs require organic substances (carbohydrates and lipids) for growth and multiplication. NOTE Autotrophs are also lithotrophs because they obtain energy either photosynthetically or oxidatively Heterotrophs are also organotrophs since they obtain energy through oxidation or fermentation of organic substances such as glucose. All bacteria that inhabit the human body are classified it to the heterotrophic or organotrophic group Fastidious bacteria need additional substances such as vitamins, purines, pyrimidines, and hemoglobin for growth and survival. Saprophytes require dead organic substances. Parasites necessitate organic substances from living tissues ACCORDING TO TEMPERATURE REQUIREMENT The optimum temperature for most clinically significant bacteria is 35 °C to 37°C. 1. Psychrophiles/Cryophiles These organisms grow well at 0 °C to a maximum of 20 °C. Examples: Listeria monocytogenes and Yersinia enterocolitica 2. Mesophiles They grow between 20 °C to 45 °C. These are the most commonly encountered pathogenic bacteria in the clinical laboratory. 3. Thermophiles/Hyperthermophiles These organisms grow between 50 °C to 60 °C, just like the archaea. Examples: Geobacillus stearothermophilus, Thermus aquaticus, Sulfolobus, Pyrococcus, and Pyrodictium ACCORDING TO TEMPERATURE REQUIREMENT 4. Extremophiles These are prokaryotes that are able to survive in unusual conditions like the absence of oxygen, increased temperature, and living below the earth's surlace. Example: Bacillus infernus (strict anaerobe) NOTE Grow @ 42°C Campylobacter jejunii Grow @ pH 3 Acinetobacter baumanni Lactobacillus acidophillus Pseudomonas aeruginosa Grow @ pH 8-10 Grow @ 65°C Vibrio Legionella Grow @