Chapter 9 Microbial growth Microbial growth MCB2004 Unit 2 Exam Review Microbial growth is the increase in number of cells o Cell elongates and DNA is replicated o Cell wall and plasma membrane begin to grow inward o Cell wall forms completely around divided DNA o Cell walls separate Know how to calculate the number of bacterial growth bacteria growth is Exponential growth Slope on a graph represents the growth rate the highest doubled slope the highest rate Bacterial growth Binary Fusion Understanding the bacterial growth curve Bacteria populations follow a sequential series of growth phases The lag log stationary and death phases Knowledge of the bacterial growth curve is critical to understanding population dynamics and population control in the course of infectious diseases in food preservation and spoilage as well as industrial microbial processes such as ethanol production There are four phases o Lag phase intense activity preparing for population growth but no increase in population cells are preparing no significant increase in number of cells o Log phase logartithmic or exponential increase in population cells are ready to reproduce see quick increase in the curve o Stationary phase period of equilibrium microbial deaths balance production of new cells o Death phase population is decreasing at a logarithmic rate Several factors affect microbial growth Physical and chemical factors Physical requirement temperature o Temperature Minimum growth temperature Optimum growth temperature Maximum growth temperature o pH pH log H Most bacteria grow between pH 6 5 and 7 5 Molds and yeasts grow between pH 5 and 6 Acidophiles grow in acidic environments o Osmotic Pressure Hypertonic environments increase salt or sugar cause plasmolysis pressure Extreme or obligate halophiles require high osmotic Facultative halophiles tolerate high osmotic pressure Normal Cell in isotonic solution o Under these condition the solute concentration in the cell is equivalent to a solute concentration of 0 85 sodium chloride NaCl Plasmolyzed cell in hypertonic solution o If the concentration of solutes such as NaCl is higher in the surrounding medium n the cell the environment is hypertonic water tends to leave the cell Growth of the cell is inhibited Plasmolysis o Irradation Chemical requirements o Carbon Structural organic molecules energy source Chemoheterotrophs use organic carbon sources Autotrophs use CO2 o Nitrogen In amino acids and proteins Most bacteria decompose proteins A few bacteria use N2 in nitrogen fixation Some bacteria use NH4 or NO3 o Sulfur In amino acids thiamine and biotin Most bacteria decompose proteins Some bacteria use SO4 2 or H2S PO4 In DNA RNA ATP and membranes 3 is a source of phosphorus o Phosphorus o Trace elements Inorganic elements in small amounts Usually as enzyme cofactors Trophisms Energy source Chemotrophs Chemoheterotrophs eg most bacteria Chemoautotrophs eg Nitrobacter NH4 NO2 Phototrophs Photoheterotrophs eg Rhodospirillum Photoautotrophs eg Cyanobacteria Autotrophs Heterotrophs use only inorganic carbon and also fix CO2 use organic compound s Carbon source Chemohetertrophs Chemoautotrophs Phtoheterotrophs Photoautotrophs The effect of oxygen on the growth of various types of bacteria Effect of oxygen toxicity of oxygen species A Obligate Aerobes need oxygen B Faculative Anareobes need oxygen but can survive without it though C Obligate Anaerobes No oxygen D Aerotolerant Anaerobes don t eat oxygen but can still survive in the presence of it E Mircoaerophiles needs a certain concentration of oxygen Chemical requirement o Organic growth factors Organic compounds obtained from the environment Culture Media Vitamins amino acids purines and pyrimidines Culture medium Nutrients prepared for microbial growth Sterile No living microbes Inoculum Introduction of microbes into medium Culture Microbes growing in on culture medium Chemically defined media Exact chemical composition is known Complex media Extracts and digests of yeasts meat or plants Nutrient broth Nutrient agar Agar liquid medium plate Complex polysaccharide Used as solidifying agent for culture media in Petri plates slants and deeps Generally not metabolized by microbes Liquefies at 100 C Solidifies 40 C Selective Media Differential Media Suppress unwanted microbes and encourage desired microbes Make it easy to distinguish colonies of different microbes Pure Culture Streak plate Understand the process of how pure cultures can be isolated by using streak plate A pure culture contains only one species or strain A colony is a population of cells arising from a single cell or spore or from a group of attached cells A colony is often called a colony forming unit CFU Bacterial Growth Viable count Pour plate method inoculate empty plate mixed with melted nutrient agar colonies grow in and on solidified medium Spread plate method After incubation count colonies on plates that have 25 250 colonies CFUs Calculation number of colonies on plate x reciprocal of dilution of sample number of bacterial ml Most Probable number Multiple tube MPN test Count positive tubes Bacterial growth direct count Measuring Microbial Growth Direct methods o Plate counts o Filtration o MPN o Direct microscopic count o Dry weight Indirect methods o Turbidity o Metabolic activity o Dry weight Lecture 10 Control of Microbial Growth Knowledge of microbiology Allows humans to control growth of microbes o Decrease growth Prevent food spoilage Prevent disease occurrence public health personal hygiene anti microbial drugs vaccine Prevent contamination in medical and in microbiological laboratories o Increase Growth Make fermented food Make medicine insulin interferon industrial products biofuel Recycle waste Biological control BT as pesticide Terminology relating to the control of microbial growth Sterilization destruction or removal of all forms of microbial life including endospores Commercial sterilization sufficient heat treatment to kill endospores of Clostridium botulinum in canned food Disinfection destruction of vegetative pathogens on living tissue Antisepsis destruction of vegetative pathogens on living tissue Degerming removal of microbed from a limited area such as the skin around an injection site Sanitization treatment intended to lower microbial counts on eating and drinking utensils to safe public health levels Actions of Microbial Control Agents Alternation of membrane permeability Damage to proteins Damage to nucleic acids
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