Exam 2 Guide LECTURE 9 MICROBIAL GROWTH Define bacterial growth including binary fission Microbial Growth The increase in the number of cells To find the number of cells just do 2 generation Compare the phases of microbial growth and describe their relation to generation time Bacterial populations follow a sequential series of growth phases the lag log stationary and death phases Lag intense activity preparation for population growth no increase in population Log Logarithmic or exponential increase in population Stationary equilibrium microbial death balance production Death population is decreasing at a logarithmic rate Classify microbes into five groups on the basis of preferred temperature range Physical Requirement Temperature Minimum growth temperature optimum growth temperature maximum growth temperature Psychrophiles prefer 10 20C optimum 10C Psychrotrophs cold tolerant bacteria that have the ability to grow in cold temperatures but have optimal temperatures of 20 C Meophiles optimum temps of 35C Thermophiles 60 C Hyperthermophiles 90 C Identify how and why the pH of culture media is controlled Physical Requirement 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 Explain the importance of osmotic pressure to microbial growth Physical Environment Hyertonic environments increase salt or sugar cause plasmolysis Extreme or obligate halophiles require high osmotic pressure Facultative halophiles tolerate high osmotic pressure Provide a use for each of the four elements carbon nitrogen sulfur and phosphorus needed in large amounts for microbial growth Chemical Environments Carbon Structural organic molecules energy source Chemoheterotrophs use organic carbon sources Autotrophs use CO2 Nitrogen Sulfur In amino acids and proteins Most bacteria decompose proteins Some bacteria use NH4 or NO3 A few use N2 in nitrogen fixation In amino acids thiamine and biotin Most bacteria decompose proteins Some bacteria use SO42 or H2S In DNA RNA ATP and membranes Phosphorus In PO43 is a source of phosphorus Trace Elements Inorganic elements in small amounts Usually as enzyme cofactors Categorize the various nutritional patterns among organisms according to energy and carbon source Trophisms Energy Source Chemotrophs Phototrophs o Chemoheterotrophs most bacteria o Chemoautotrophs Nitrobacter NH4 NO2 o Photoheterotrophs Rhodospirillum o Photoautotrophs Cyanobacteria Carbon Source Autotrophs use only inorganic carbon and also fix CO2 Heterotrophs use organic compounds Obligate aerobes only aerobic growth Facultative anaerobes both aerobic and anaerobic growth Obligate anaerobes only anaerobic growth Antitolerant anaerobes only anaerobic growth but continuous in the Explain how microbes are classified on the basis of oxygen requirements a b c d presence of oxygen e concentration Forms of Oxygen Reactive Oxygen Species Singlet oxygen O2 boosted to a higher energy state Microaerophiles Only aerobic growth but oxygen is required in low Superoxide free radicals O2 O2 2H superoxide dismutase H2O2 O2 Peroxide anion O22 2 H2O2 catalase 2 H2O O2 H2O2 2O peroxidase 2 H2O Hydroxyl radical OH Distinguish between chemically defined and complex media Culture Media Inoculum induction of microbes into medium Culture medium nutrients prepared for microbial growth Sterile no living microbes Culture Microbes growing in on culture medium Chemically defined media Complex media Nutrient broth or agar Extracts and digests of yeasts meat or plants Exact chemical composition known Agar Liquid medium plate Complex polysaccharide used as solidifying agent for culture media in Petri plates slants and deeps Generally not metabolized by microbes Liquifies at 100C solidifies at 40 C Selective Media Suppress unwanted microbes and encourage desired microbes Differential Media Make it easy to distinguish colonies of different microbes Define colony and pure culture 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 Describe how pure cultures can be isolated by using the streak plate method Bacterial growth Viable count After incubation count colonies on plates that have 25 250 CFUs Most Probable Number Multiple tube MPN test count positive tubes and compare with a statistical table Explain direct and indirect methods of measuring cell growth Direct Count 1 Bacterial suspension is added and fills the shallow volume over the squares by capillary action 2 The depth of the squares are known so the volume of the bacterial suspension over the squares can be calculated depth x area 3 Microscopic count all cells in several large squares are counted and the numbers are averaged 4 Multiply the number of cells by the volume Plate counts Filtration MPN Direct microscopic count Dry weight Indirect count Turbitidy with spectrometer Metabolic activity Dry weight Study Questions 1 Assume you inoculated 100 facultatively anaerobic cells onto nutrient agar and incubated the plate aerobically You then inoculated 100 cells of the same species onto nutrient agar and incubated the second plate anaerobically After incubation for 24 hours you should have a more colonies on the aerobic plate b more colonies on the anaerobic plate c the same number of colonies on both plates 2 The term trace elements refers to a the elements CHONPS b vitamins c nitrogen phosphorus and sulfur d small mineral requirements e toxic substances 3 Which one of the following temperatures would most likely kill a mesophile a 50 C b 0 C c 9 C d 37 C e 60 C a antibiotic resistance b hydrogel c iron deficiency d quorum sensing a selective media b reducing media c enrichment media d differential media 4 Which of the following is not a characteristic of biofilms 5 Which of the following types of media would not be used to culture aerobes e complex media 6 An organism that has peroxidase and superoxide dismutase but lacks catalase is most likely an a aerobe b aerotolerant anaerobe c obligate anaerobe LECTURE 10 Control of Microbial Growth Define the following key terms related to microbial control sterilization disinfection antisepsis degerming sanitization Sterilization destruction of all forms of microbial life including endospores usually by steam under pressure or a sterilizing gas such as ethylene oxide Disinfection Destruction of vegetative
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