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BIO 205 – Microbiology Chapters 8, 9, end of Ch. 3 Chapter 8 - Growth of Microorganisms Key words / concepts • doubling / generation time • binary fission • the growth phases of a population • lag, exponential, stationary, death • colony • biofilm • trance elements vs. growth factors • temperature “requirements” • oxygen requirements • pH and salt “requirements” • bacterial counts • dilution plating / spread plate technique How do most bacteria replicate? Some do it a bit different . . . Listeria monocytogenes Generation time Growth Phase Continuous culture in a chemostat Types of Growth Streak plate technique Biofilms Biofilms and quorum sensing Biofilms Microbial nutrition Microbial nutrition Trace elements Growth factors Nutritional classes of microorganisms carbon from CO2 Defined media Produced from pure chemicals Complex media Extracts of natural sources ▪ Beef, blood, milk, protein, yeast, soybeans ▪ Precise composition not known Selective media Contents select for specific microorganism Differential media Identification of microorganisms Defined media none Complex media Nutrient agar Mueller Hinton agar - antibiotic testing Selective media EMB - inhibit growth of Gram positive bacteria MacConkey - inhibit growth of Gram positive bacteria Mannitol salt - high salt (staph will grow) Differential media Sheep Blood agar - hemolysis EMB - lactose and/or sucrose fermentation - fecal coliforms MacConkey - lactose fermentation Mannitol Salt - mannitol fermentation - pathogenic staph Enterotube - rapid ID of enteric bacteria (15 tests in 1) Synder - dental caries susceptibility - acid producers in saliva How temperature affects growth Oxygen requirements aerobe anaerobe obligate / strict facultative microaerophile aerotolerant Oxygen culturing conditions • Culturing – Shaking machines • Increase oxygen in the media – Candle jars • Not anaerobic but reduces available oxygen – Anaerobic chambers • All oxygen is replaced with other gas Figure 3.25 How do we visualize oxygen requirements in the lab? (stab vs. broth) pH and salt and bacterial growth halophilic How do you know how much bacteria there is? How do you know how much bacteria there is? Hemocytometer Viable count = dilutions and plating Pour vs. spread plate technique Plate count A little math for you! plate 1 ml of bacteria onto agar plate 5348 672 126 28 Summary - Growth of Microorganisms Chapter 9 - Controlling Microorganisms How we used to protect ourselves from microbes Sterilization Disinfection / sanitizing Decontamination Antiseptics / antisepsis Bactericide vs. Bacteriostatic Methods of Physical Control Heat • moist heat • dry heat cold Preserving cultures • Cold storage – Short-term: refrigeration slows growth • Must continually transfer – Long-term: freezing • Add substance to reduce freeze-killing – Glycerol, skim milk, dimethyl sulfoxide (DMSO) – Lyophilization • Long term—freeze drying • Frozen and dried under vacuum • probiotics Methods of Physical Control autoclave incineration Sterilization Eliminating all microorganisms Culture media must be sterilized Heat sterilization Moist heat ▪ Autoclave ▪ 121oC for 20 minutes Dry heat ▪ 170oC for 90 minutes Figure 3.20 Methods of Physical Control pasteurization Thermal Death What? Thermal Death Time Thermal Death Point Methods of Physical Control Radiation • nonionizing (UV) • ionizing Methods of Physical Control Methods of Physical Control Filtration Lyophilization Methods of Chemical Control germicides - activity classified as high intermediate low Assignment for next week: What do you use (at home or work)? How does it work? Methods of Chemical Control •Phenols / phenolics •Alcohol Methods of Chemical Control • Halogens • Hydrogen Peroxide Methods of Chemical Control •Heavy metals • Surfactants / detergents Testing germicides we will do Nov. 9 Testing germicides Highest Concentration Of toxin Less light = higher concentration of toxin = less bacteria still alive Preserving Food Preserving Food Fig. 1. Flow diagram of the main routes of spore contamination into foods. A circled Sp indicates possible environments for formation of endospores (sporulation).
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