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Microorganisms- Microorganismso Prokaryotic cells – no nucleus, characterized by simplicityo Photosynthetic autotrophso Chemosynthetic autotrophso Heterotrophs- Reproductiono Reproduced by binary fission – splitting into two every 20-30 minutesunder optimal conditionso Mechanism simpler than for eukaryotic cellso Simplicity gives potential for very rapid population growth- Plasmidso Circular piece of DNA that carries only a few geneso Replicate independently of the main chromosomeo Number of plasmids in a cell remains consistent from generation to generation o F plasmids permit conjunction, R plasmids carry resistance genes and carry genes for antibiotic resistance- Bacteriao Types Gram positive Gram negative Anaerobic Aerobic Spore forming Non-spore forming Heterotrophic Autotrophic- Factors that affect growtho Nutrients  Some can survive on carbon, nitrogen, and a trace of few minerals Others need a more complete source of nutrients – fastidious.  Most food poisoning organisms are fastidious. o pH  Refers to relative acidity of the medium,  As pH decreases the amount of present acid increases Most microorganisms grow best around a pH of 7 Some are very acid tolerant No pathogenic organisms can grow at a pH below 4.6 Some spoilage organisms can grow at low pH valueso Oxygen tension Aerobic organisms require oxygen to grow Anaerobic organisms find oxygen toxic and will die in its presence Facultative organisms can grow with or without oxygen, most grow better witho Temperature Psychrophilic – grow best around 20 degrees C or below Mesophilic – grow best between 20-40 degrees C Thermophilic – grow best about 50 degrees C Thermoduric – capable of survival above normal pasteurizationo Water activity Availability of water to enter into chemical reactions Ranges from 0-1, activity of pure water being 1 Presence of salt, sugar or other substances that can bind water will lower the water activity of a substance Some are capable at growing at low water activities, others are not In many foods, presence of salts and sugars control the growth of undesirable organismso Presence of other microorganisms Presence of many harmless organisms can slow growth of few harmful ones Some organisms secrete substances into the growth medium that inhibit the growth of other organisms (ex. Penicillin) Bacteriocins – produced by some organisms and inhibit the growth of other


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OSU FDSCTE 2200 - Microorganisms

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