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UM BIOM 250N - Microbial Growth and Control
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BIOM 250 1st Edition Lecture 9Outline of Last Lecture I. Biotechnology and Recombinant DNAII. Restriction EnzymesIII. Polymerase Chain ReactionsIV. PCR ProtocolOutline of Current LectureI. Physical RequirementsII. Chemical requirementsIII. BiofilmsIV. CommunicationV. Bacterial GrowthVI. Control of GrowthVII. Effectiveness of TreatmentCurrent LectureI. Physical Requirements for Microbial Growtha. Temperature- most microbes favor growth within a limited rangei. Common groups are:ii. Psychorophiles- cold-lovers; usually below 30 degrees Celsiusiii. Mesophiles- thrive at moderate temperatures (30-50 degrees Celsius)iv. Thermophiles-thrive at high temperaturesv. Temperature is used to preserve food1. Refrigeration slows growth of microbes which prevents spoilage2. Heating kills bacteria and endosporesb. pH- most microbes have a narrow pH range for growthi. metabolic fermentation can lower pH to stop growth and kill bacteria c. Osmotic pressure- hypertonic solutions cause plasmolysis (cell shrinkage)i. High sugar or salt solutions are used to preserve foodsII. Chemical Requirements for Microbial Growtha. Oxygen- very reactive; essential but can be dangerousThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.b. Microorganisms in groups are based on oxygen requirements:i. Obligate aerobes- oxygen requiredii. Obligate anaerobes- only anaerobic; inhibited by oxygeniii. Facultative anaerobes- grows with and without oxygen—but faster without oxygeniv. Aerotolerant- anaerobic growth but tolerates oxygenv. Microaerophiles- requires low oxygen concentrationc. Environment for colonization/disease- refers to the oxygen concentration in the location of the diseased. Reactive oxygeni. Superoxide radicals produced by normal cell respirationii. Very damaging to cell componentsiii. Superoxide dismutase produced to neutralize oxygen radicalsiv. Superoxide also used in cell defense during phagocytosisIII. Biofilmsa. Most studies of microbial growth are done in liquid culture or on defined media surfacesb. In natural settings, bacteria aggregate with themselves, other bacteria, or other organisms to form multicellular structuresc. Biofilm structure:i. Unbalanced growth patternii. Microbial mats- assemble at air-liquid interfaceiii. Biofilms- assemble at solid-liquid interfaced. Biofilm locations:i. Environmental surfaces, rivers, soils, animals, etc.ii. Industrial pipes, ship hulls, cooling surfacesiii. Food, including edible, waste and productioniv. Dental surfaces, medical devices, body organse. Biofilm Formation:i. Attachment:1. Loose bacteria can reversibly attach to a surface2. Flagella, pili, and adhesive matrix proteins start the process3. Secreted polysaccharides produce the matrixii. Maturation:1. Cell multiplication and motility occurs across the surface2. Open areas and channels are actively maintained during growthiii. Matrix:1. Secreted extracellular material holding bacteria in place2. Gelatinous with porosity3. Mostly polysaccharides but also includes proteins, lipids and nucleic acidsiv. Antimicrobials:1. Biofilm bacteria have higher tolerance for antimicrobials than planktonic bacteriaIV. Bacterial Cell to Cell Communicationa. Bacterial pheromones are diffusible molecules that elicit a response after contactwith a specific receptor on or in the target celli. This initiates a signal cascade that alters gene expression and/or cell behaviorii. Usually specific to a bacterial speciesV. Bacterial Growtha. Binary fission:i. A single bacterium replicates its genomeii. New membrane is formed and splits cells into two individualsb. Generation time:i. Dependent on organism and its environmentii. Defined as time required for a population to doubleiii. Exponential growth can cause harmful increase in bacteria in a short amount of timec. Growth stages:i. Lag phase- metabolic activity/synthesis is required to divide. This stage can last hours to daysii. Log phase- logarithmic or exponential growth—growth is constant if nutrients are availableiii. Stationary phase- bacterial deaths are equal to the new growth occurring—this is due to waste products and lack of nutrientsiv. Death phase- the amount of deaths occurring exceed the new growth andthe media is exhaustedVI. Control of Microbial Growtha. Definitions:b. Sepsis-microbial contamination or diseasec. Asepsis- absence of significant contaminationd. Sterilization- destruction of all microbial lifee. Commercial sterilization- enough heat to kill endosporesf. Disinfection- death of vegetative—live/growing—cells but NOT endospores (usually refers to a surface)g. Antisepsis- removing pathogens from living tissueh. Biocidal/bactericidal/germicidal- kills microorganisms—but not endosporesi. Bacteriostatic-inhibits growth and multiplicationj. Sanitization- lowers the amount of bacteria to safe public health levelVII. Effectiveness of Treatmentsa. Effectiveness of treatments in dependent on:i. The number of microbesii. The environment1. Organic matter, such as blood and feces, can lower disinfectant concentration2. Temperature- fats and proteins can protect microbes from heat treatment3. Biofilms- treatment must pass to the interior of the biofilm iii. Time of exposure1. Some microbes are more resistant2. Some disinfectants are slow to penetrate and activ. Microbial characteristics1. LPS in gram –‘s are protective against many biocides2. Pseudomonas are resistant to and sometimes grow in certain disinfectantsa. Also resistant to many antibiotics and are able to metabolize many substances such as soap and cap glue3. Mycobacterium tuberculosis has a protective lipid-rich cell


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