Microbial Growth and Control PDF

Microbial Growth and Control Ch. 7 and 11 Jabiru, world’s biggest stork! Belize Ch. 7 Microbial Nutrition, Ecology, and Growth Microbes by Carbon source – Autotrophy or Heterotrophy Nutritional...

Microbial Growth and Control Ch. 7 and 11 Jabiru, world’s biggest stork! Belize Ch. 7 Microbial Nutrition, Ecology, and Growth Microbes by Carbon source – Autotrophy or Heterotrophy Nutritional Type Energy source – Chemotrophy or Phototrophy Nutritional Requirements For energy needs and building organic molecules: ◦ Carbon, nitrogen, phosphorous, sulfur (What types of macromolecules contain these elements?) Trace elements (mostly enzyme co-factors): ◦ K, Na, Cl, Mg, Ca, Fe, Zn, Mo (found in anaerobic respiratory enzymes) Vitamins and other organic growth factors (co-enzymes) ◦ Ex. Niacin is a precursor for NAD+ What about Oxygen? Five Categories: 1. Obligate aerobes – use aerobic respiration (only) 2. Facultative anaerobes – use aerobic respir. if O2 available, anaerobic pathways (ferm., anaer. respir. if not) 3. Microaerophiles – use aerobic respir. but need low [O2] 4. Obligate anaerobes – do not use aerobic respir., find O2 toxic! 5. (Aerotolerant anaerobes – do not use O2 but can survive in its presence, we cannot detect this O2 category in lab) O2 Toxicity End of ETC in aerobic respiration: e- + O2 + H+ H2O O2- (superoxide – highly reactive, damages DNA, proteins, etc.) Superoxide dismutase (SOD): O2- + H2O 🡪 H2O2 Catalase: H2O2 🡪 H2O + O2  Physical Requirements for Growth 1. Temperature What is responsible for the sharper cutoff on the high side? The more gentle slope on the low side? 2. pH Most cells prefer neutral range pH 5-9 Acidophiles ex. Helicobacter pylori Fermenters 🡪 build-up of lactic acid can make media toxic ◦ Prevent with buffers 3. Osmotic Pressure [solute] inside cell vs. [solute] outside cell = Isotonic > Hypotonic < Hypertonic Plasmolysis Salt and sugar as food preservative Halophiles ex. Staphylococcus aureus Why can bacteria survive in pure water without exploding? Why do human rbc’s explode in pure water? Bacterial Growth Growth = increase in number, not increase in size Most bacteria reproduce using binary fission Bacterial Growth Curve What would the growth curve look like if a new food source became available when the culture is in stationary phase?  Ch. 11 Physical and Chemical Agents for Microbial Control Raggiana Bird-of-Paradise Papua New Guinea Microbial Control Terms Factors that influence how effective microbial control methods are: Time and temperature ◦ Chemical agents slower at colder temps Type and number of microbes ◦ Some microbes more difficult to kill ◦ Most difficult? Physiologic state of the microbes ◦ Lots of metabolic activity 🡪 easier to disrupt ◦ Lower growth rates 🡪 takes longer to kill Environment the microbes are in ◦ Some chemical agents are deactivated by presence of other organic compounds (blood, pus, fecal waste, etc.) Physical Methods of Control 1. Heat – denatures proteins ◦ Dry Heat: incineration, oven ◦ Moist Heat: Boiling – spores? Autoclave – 121oC for 15 min., results in sterilization ◦ Pasteurization What can you do if the thing you need to sterilize is heat labile? 2. Filtration – blocks microbes ◦ Pore size 0.45 µm catches all bacteria 0.05 µm catches virus 3. Low Temperatures and Drying ◦ Refrigeration – bacteriostatic ◦ Dessication – spores survive ◦ Lyophilization – freeze-drying 4. Osmotic Pressure ◦ Plasmolysis 5. Radiation – damages DNA and proteins ◦ Ionizing: great penetration ex. X-rays and gamma-rays ◦ Non-ionizing (UV): good for surfaces  Chemical Control Methods 1. Soaps and detergents –surfactants, damage membranes ◦ Quaternary ammonium compounds (Quats) Effective surface disinfectants 2. Phenol and derivatives – damage membranes and denature proteins ◦ Not inhibited by organic materials ◦ Ex. Lysol, Chlorhexidine 3. Alcohols – denature proteins, damage membranes ◦ Safe for skin ◦ Evaporate quickly 4. Halogens – damage proteins ◦ Chlorine – used to sanitize water, active ingredient in bleach ◦ Iodine – great antiseptic 5. Heavy metals – damage proteins ◦ Silver nitrate – eye drops for newborns ◦ Organic mercury – antisepsis 6. Organic acids – bacteriostatic by slowing/preventing fermentation ◦ Mostly used as food preservatives 7. Oxidizing agents – break disulfide bridges in proteins ◦ Peroxide - antisepsis Black-bellied Whistling Duck Gulf Coast of Texas