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  • 1. MICROBIALGROWTH REQUIREMENTS:INCREASE IN NUMBEROF MICROBIAL CELLSPhosphorusOrganic growthfactorsTrace elementsPhysicalTEMPRATUREpHOsmotic pressureCHEMICALHydrogenOxygen (O)Nitrogen (N)Sulfur (S)CHAPTER 6MICROBIAL GROWTH-
  • 2. PHYSICAL REQUIREMENTS for GROWTH :• MINIMUM GROWTHTEMPERATURE– Lowest temperature atwhich a species willgrow• OPTIMUM GROWTHTEMPERATURE– Temperature at whichspecies will grow best• MAXIMUM GROWTHTEMPERATURE– Highest temperature atwhich growth is possibleTEMPERATURE
  • 3. CLASSIFICATION OF MICROBES:• PSYCHROPHILES - Cold loving microbes• Optimum growth temperature: 15oC• Capable of growing at 0oC, but not at 250C• Found in ocean depths, polar regions– Psychrotrophs-less temperature sensitive, some foodsspoilage• MESOPHILES - moderate temperature loving microbes– Optimum growth temperature: 25c -40 c– Most common microbes– Food spoilage and disease• THERMOPHILES heat loving microbes• Optimum growth temperature: 50-60oC• Minimum growth temperature: 45oC• Found in hot springs, compost pilesTEMPERATURE RANGE of GROWTH
  • 4. ACID BASE CHEMISTRY– ACID – a substance thatdissociates intohydrogen ions (H+) andnegative ions in aqueoussolutionEx. Hydrochloric acid,citric acid– BASE – a substance thatdissociates intohydroxide ions (OH-) andpositive ions in aqueoussolutionEx. Sodium hydroxide
  • 5. • pH – potential hydrogenLogarithmic scale used to measure H+concentration– Most bacteria grow between pH 6.5 to 7.5– Molds and yeast grow between pH 5 to 6– Acidophiles grow in acidic environmentsBUFFERS – compounds that keep pHfrom changing drastically; ex.peptones, amino acids, phosphatesalts-very important in the preparationof microbial MediaPHYSICAL REQUIREMENTS for GROWTH cntd.:pH
  • 6. PHYSICAL REQUIREMENTS for GROWTH cntd.Osmotic Pressurethe force used by a solvent in moving from an area with alower solute concentration to an area of higher soluteconcentration– Hypertonic environments - concentration of solute(ex. salt or sugar) is higher outside cell, causesplasmolysis• Results in loss of water from a cell–Inhibits bacterial growth–Used to preserve food, ex.Salted fishHalophiles - require higher saltconcentrations in their environment
  • 7. CHEMICAL REQUIREMENTS for GROWTHCarbon– Structural, organicmolecules, energysourceChemoheterotrophsuse organic carbonsourcesEx. Humans, fungi,protozoa, mostbacteria,helminthsAutotrophs-use CO2 ascarbon sourceEx. PlantsNitrogenIn amino acids, proteinsSulfureIn amino acids, thiamine, biotinPhosphoreIn DNA, RNA, ATP, membranesPO43−is a source of phosphorusTrace ElementsInorganic, required in smallamounts; Ex.: Fe, Cu, Mb, ZnOrganic FactorsOrganic, from environmentVitamins, amino acids, purinespyrimidines
  • 8. CHEMICAL REQUIREMENTS for GROWTHcntd. - OXYGENObligateaerobes-O2isrequired forgrowthFacultativeanaerobes-growth canoccur whenO2 notpresentObligateanaerobes-no growthwhen O2present-harm byO2Aerotolerantanaerobes-can tolerateO2 but can’tuse it forgrowthMicro-aerophilesneed very lowO2concentrations
  • 9. TOXIC FORMS of OXYGENProduced in small amounts during normal metabolicprocesses-harmful to cellsSome Forms of Toxic Oxygen– Superoxide free radicals (O2-1) – very unstable, steal electronsfrom cellular molecules– Peroxide anion (O2-2) – contained in hydrogen peroxide– Hydroxyl radicals (OH-) – most reactiveMECHANISMS of ELIMINATIONSuperoxide free radicals (02-1)02-+ 02-+ 2H+ superoxideH202 + 02dismutasePeroxide anions (02-2)2H2O2 catalase 2H2O + O2peroxidase
  • 10. ANAEOBIC CULTURE METHODS3. ANAEROBIC JAR 4. ANAEROBIC _________1.Reducing mediacontains chemicals (sodium thioglycolate) that combine with O2Media is heated to drive off O22. OxyPlatesenzyme (oxyrase) that reduces oxygen to water is added to growthmedia, transforms petri plate into an anaerobic chamber
  • 11. CAPNOPHILESDef.: Bacteriathat requireCO2concentration
  • 12. Figure 6.5BIOFILMS• Microbialcommunities• Form slime orhydrogels– Bacteria attractedby chemicals viaquorum sensing• Share _________• __________ fromharmful factors
  • 13. • Culture Medium: Nutrient (or any material) prepared for thegrowth of microbes in a laboratory• Sterile: No living microbes• Inoculate: Introduction of microbes into media• Culture: Microbes growing in/on culture medium• Pure culture - contains only one species or strain of bacteria• Agar: Complex polysaccharide (from marine algae)– Used as solidifying agent for culture media in Petri plates,slants, and deeps– Generally not metabolized by microbes– Liquefies at 100°C– Solidifies ~40°CCULTURE MEDIAimportant terms
  • 14. CULTURE MEDIAChemically Defined Media: Exactchemical composition is knownComplex Media: Extracts and digestsof yeast, meats (organs), or plantsEx. Nutrient broth, nutrient agar
  • 15. CULTURE MEDIUM forFastidious MICROORGANISMS
  • 16. BOTH SELECTIVE and DIFFERENTIAL MEDIA1.McConkey Agar2.EosinMethylen blue AgarDIFFERENTIALSELECTIVE forgramnegative
  • 17. • Supress unwanted microbes andencourage desired microbes.Ex. Eosin Methylene Blue Agar (EMB) andMacConkey Agar-allow Gram (-)bacteria togrow but not Gram (+) bacteria.SELECTIVE MEDIAFigure 6.9b, cEMB Agar
  • 18. • Used to distinguish colonies of differentmicrobes: Ex. Lactose fermenting bacteriafrom lactose non-fermenting bacteria; Ex.:MacConkey agar and EMB agarDIFFERENTIAL MEDIAFigure 6.9aLactose nonfermenter onMacConkey AgarLactose Fermenter onMac Conkey Agar
  • 19. ENRICHED/DIFFERENTIAL MEDIAnutritionally fortified media which encourages thegrowth of a wide range of microorganismsBlood Agar Plate
  • 20. STREAK PLATE METHODPROCEDURE for STREAKINGfor isolationIsolated COLONIES on AGARPLATEColony- a population of cells arising from a single cell or spore or from a group of attached cellsA colony is often called a colony-forming unit (CFU)
  • 21. • Deep- Freezing: -50°to -95°C• Lyophilization (freeze-drying):Frozen (-54° to -72°C) and dehydrated in avacuumPRESERVING BACTERIALCULTURES
  • 22. Reproduction in PROKARYOTES• Binary Fission• Budding• Conidiospores(actinomycetes)• Fragmentation offilamentsBinary fission
  • 23. Figure 6.13Bacterial Exponential Growth CurveGenerationTIME:20mnTime required fora cell to double innumber
  • 24. Figure 6.14FOUR TYPICAL PHASES ofBACTERIAL GROWTH CURVE
  • 25. METHODS to DETECT and MEASUREBACTERIAL GROWTH (numbers)• DIRECT– Plate Counts*– Filtration– Most ProbableNumber (MPN)–DIRECTMicroscopicCount*• INDIRECT– TurbidityMeasurements*– Dry WeightDetermination– Metabolic ActivityMeasurements*
  • 26. • InoculatePetri platesfrom serialdilutions• Used to countlivingbacterial cellsonly.DIRECT PLATE COUNT METHODFigure 6.16Plate Count Method
  • 27. DIRECT MICROSCOPIC COUNTThe number of microbes in a specific volume of bacterial suspension are counted using a special slideEx.: PETROFF HAUSSERDoes not distinguish betweenliving and dead
  • 28. TurbidityEstimating Bacterial Numbers by IndirectMethodsFigure 620:Indirectly Measures number of cells present, dead or live
  • 29. Estimating Bacterial Numbers byINDIRECT Methods• Metabolic activity– Amount of certain metabolic products is indirect proportion to number of bacteriapresent– Examples:» Oxygen Consumption» Acid Production• Dry weight– Weight of packed cell mass is proportionalto the number of cells in culture– Used for filamentous Fungi