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Microbiology – Alcamo Growth and Growth Phases Growth • Human Terms: Growth = Larger • Microorganism Terms: Growth = More Growth • Binary Fission – bacteria reproduce asexually: – Chromosome duplicates – Cell elongates – Plasma membrane pinches in at center – Nuclear material distributes evenly – Cell wall thickens to separate dividing cells Growth • Binary fission – gives immortality to bacteria • The first bacterium never dies • It reproduces and becomes a new, young cell again • The original bacterium (billions of years old) is still among us Binary Fission United Streaming • http://player.discoveryeducation.com/in dex.cfm?guidAssetId=F59553CB-5A474CA7-88E56D2A0BB0DAE4&blnFromSearch=1&pr oductcode=US Growth Reproduction Binary Fission 20 Generation 21 Generation 22 Generation 23 Generation Generation Time • Time between cell divisions when bacteria grows and develops its unique features • Also called “Doubling Time” • A determining factor in the amount of time that passes between entry of an organism into our bodies and the appearance of disease symptoms Growth • Each microorganism has it’s own characteristic generation time • Range: – Usually 1 to 3 hours – Minimum 20 minutes (E. coli) – Maximum 33 hours (T. pallidum syphilis) BACTERIAL GROWTH IS LOGARITHMIC Growth Growth Rates • If after 48 hours of incubation, a colony is pinpoint size, long GT is indicated. • If after 48 hours, the colony is ¼” wide, short GT is indicated. Growth Example E. coli has a 20 minute generation time under ideal conditions: Time # of Bacteria 0 1 1 hour 8 2 hours 64 3 hours 512 10 hours > 1 billion 36 hours Cover face of the earth Growth Growth Rates • Exponential growth signifies ideal conditions and maximum reproduction • But the reproductive potential of bacteria is never fully realized due to environmental limitations Growth Phases • Many dynamics affect the population of bacteria over the course of time • A certain population’s history may begin when: – Several bacteria enter the human respiratory tract – Several bacteria are transferred to a tube of growth medium in a lab Growth Phases Lag Phase: • First few hours of growth curve • Period of adjustment to new environment • If an infection, WBC’s can be engulfing some cells • If in a lab, some cells may die from transfer shock Growth Phases • The activity of the remaining cells is intense as they: – Store nutrients – Synthesize enzymes – Prepare for binary fission • But the curve remains at a plateau, where the number of cells reproducing equals the number of cells dying Growth Phases Log Phase: • Also called “exponential” phase • The mass of each cell increases rapidly and reproduction follows • As each generation time passes, the number of bacteria doubles and the graph rises quickly Bacterial Growth • http://www.bing.com/videos/watch/vide o/teachertube-bacterialgrowth/74899e842ef0b09ab27174899e8 42ef0b09ab271287095849258?q=bacterial%20growth% 20videos Growth Phases • In humans, disease symptoms arise during the log phase – Bacterial population is high enough to cause damage – Fever, coughing, tissue damage arise • In a lab, visible signs of growth will be seen: – colonies will appear on solid media – broth media will become cloudy Growth Phases • Research experiments are usually done during the log phase because the population of bacteria is at its maximum potential Growth Phases Stationary Phase: • Period of even population numbers • Reproduction rate = death rate • No change in total number of bacteria Growth Phases • Stationary Phase: • In humans: – the immune system may be destroying the bacteria – antibiotics have been administered • In the lab: – nutrients are becoming scarce – waste products are building up – oxygen or water could be in short supply Growth Phases Decline Phase: • Environment becomes progressively worse and exerts its limiting powers – pH is changing – oxygen and nutrients are scarce – accumulation of toxins Growth Phases • Decline Phase: • Number of cells dying exceeds the number of new cells formed – Spore forming species will start to produce spores – Flagellated species will try to move to a new location – For other species, culture death is eminent Things That Affect Growth Temperature • Different species grow at different temperatures – Psychrophiles – grow best between 0oC and 20oC – Mesophiles – grow best between 20oC and 20oC – Thermophiles – grow best between 40oC and 90oC Things That Affect Growth Temperature • Most bacteria are Mesophiles, especially pathogenic bacteria that grow in the human body (37oC) • When the body’s temperature rises to 40oC (104oF) there is a slightly negative affect on bacterial growth • The lab incubator is set at 37oC to encourage bacterial growth Things That Affect Growth Temperature • Some mesophiles can grow at refrigerator temperatures and cause food spoilage • Staphylococci can grow in the refrigerator and deposit their toxins on cold cuts, salads and leftovers • If these foods are eaten without further cooking, food poisoning can result Things That Affect Growth Temperature • Salmonella outbreak in a restaurant in 1991 • Restaurant employee prepared Caesar salad dressing which contains raw egg • It may have remained at room temperature too long before being served • Within 3 days, 15 people were ill with diarrhea, fever, cramps and vomiting Things That Affect Growth Oxygen • Aerobic bacteria – require oxygen to grow • Anaerobic bacteria – require an oxygenfree environment to grow – Includes Clostridium species that cause tetanus and botulism • Facultative bacteria – grow in either the presence or absence of oxygen – includes many staphylococci, streptococci and bacilli Things That Affect Growth pH • Bacteria have a neutral internal environment • Will tolerate a pH range of 6.5 – 7.5 • Human blood and tissues have a pH of ~7.2 – 7.4 • Provides a suitable environment for disease causing bacteria to grow Things That Affect Growth pH • Certain bacteria are acid-tolerant • Useful in the food and dairy business • Lactobacillus and Streptococcus produce the acid that converts: – milk to buttermilk – cream to sour cream – milk curds to cheese • These bacteria pose no threat to good health even when eaten in large quantities Things That Affect Growth pH • Most bacteria do not grow well under acidic conditions • Stomach’s acidic environment prevents disease • Certain acidic foods are hardly ever contaminated with bacteria – Citrus fruits – Cabbage – Tomatoes Things That Affect Growth Pattern of Nutrition • Bacteria (like us) need: –water –foods to serve as energy sources and as raw materials for synthesis of cell components Things That Affect Growth Pattern of Nutrition • Two patterns for obtaining nutrition: – Autotrophy – can make their own food using inorganic carbon, water and sun’s energy – Heterotrophy – obtain preformed organic molecules from the environment for structural components and energy • Saprobes – feed exclusively on dead organic matter such as rotting wood • Parasites – feed on living organic matter such as human tissues Things That Affect Growth Bacterial Cultivation • In the lab, bacteria are grown in: – nutrient broth containing water, beef extract and peptone (protein supplement) – nutrient agar – contains the same, plus agar, a polysaccharide derived from marine algae *Most bacteria grow well in these Things That Affect Growth Bacterial Cultivation • Some bacteria require enriched or specialty media • The streptococci that cause strep throat and scarlet fever grow well when whole blood is added to the media • Blood agar – heated before solidification to disrupt the red blood cells and release hemoglobin • Sometimes called chocolate agar Things That Affect Growth Bacterial Cultivation • Selective media – contain ingredients to inhibit the growth of certain bacteria in a mixture while promoting the growth of others – Mannitol salt agar – high salt content inhibits the growth of most bacteria, but allows for staphylococci to grow – Eosin methylene blue agar – contain dyes that inhibit Gram-positive bacteria, but allow growth of Gram-negative Things That Affect Growth Bacterial Cultivation • Differential Media – makes it easy to distinguish colonies of one organism from colonies of another on the same plate • MacConkey’s agar contains red dyes as well as lactose – Colonies of bacteria that ferment lactose are red – Colonies of bacteria that don’t ferment lactose are colorless Things That Affect Growth Bacterial Cultivation • Natural Media – not chemically defined – Exact components and quantities are not known – Some bacteria will only grow on natural media • Synthetic Media - chemically defined – The nature and amount of each component is known Things That Affect Growth Intermicrobial Relationships • Symbiosis – situation in which two populations of organisms interact in a close and permanent association • Benefits obtained may involve: – food – protection – support Things That Affect Growth Intermicrobial Relationships • Mutualism – symbiosis that benefits both populations • Bacteria living on roots of plants: – Bacteria trap nitrogen for plants to synthesize amino acids – Plants provide a stable environment and growth factors for bacteria Things That Affect Growth Intermicrobial Relationships • Commensalism – one population receives benefit from the relationship while the other is not helped or harmed • Bacteria that inhabit human skin: – Bacteria has a place to live and food – We are not helped or harmed in any way Things That Affect Growth Intermicrobial Relationships • Synergism – two populations live together and accomplish what neither could alone • Trench mouth – two populations of bacteria (usually rods and spirochetes) must be present for infection of the oral cavity to occur Things That Affect Growth Intermicrobial Relationships • Parasitism – symbiosis is beneficial to one population (parasite) but harmful to the other (host) • The bacteria of all human diseases are parasites Applications • Industrial: Recover growth products • Penicillin Wine Beer Alcohol Vinegar Pickles Cheese Medical: Phases of disease parallel growth phases of pathogen