bauman mm ch06 for lecture - york college of pennsylvaniafaculty.ycp.edu/~cmathur/micro ch 6.pdf ·...

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MicrobiologyWith Diseases by Taxonomy

Second Edition

PowerPoint® Lecture Slides

PART A

Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings

6Microbial Nutrition and Growth


What is microbial growth?

an increase in a population of microbes rather than an increase in size of an individualcolony – an aggregation or clone of cells arising from single parent cell that is growing on solid mediaReproduction results in growth

Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings Table 6.1 Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings

Sources of Carbon, Energy, and Electrons

Organisms are categorized into two groups based on source of carbonThose using an inorganic source of carbon (carbon dioxide) are autotrophsThose catabolizing reduced organic molecules (proteins, carbohydrates, amino acids, and fatty acids) are heterotrophs


Sources of Carbon, Energy, and Electrons (continued)

Organisms categorized into two groups based on whether they use chemicals or light as source of energyThose that acquire energy from redox reactions involving inorganic (lithotrophs) and organic (organotrophs) chemicals are chemotrophsThose that use light as their energy source are phototrophs


Four Basic Groups of Organisms

Figure 6.1

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Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings Figure 6.3a-d

6 Categories of oxygen tolerance

Plus microaerophiles


Oxygen tolerance


Classification of Organisms Based on Oxygen Requirements

Aerobes – undergo aerobic respirationAnaerobes – do not use aerobic metabolismFacultative anaerobes – can maintain life via fermentation or anaerobic respiration or by aerobic respirationAerotolerant anaerobes – do not use aerobic metabolism but have some enzymes that detoxify oxygen’s poisonous formsMicroaerophiles – aerobes that require oxygen levels from 2-10% and have a limited ability to detoxify hydrogen peroxide and superoxide radicals


Examples of toxic oxygen products

Singlet Oxygen: high energy stateSuperoxide free radicalsSOD (super oxide dismutase): inactivates radicalsCatalase: neutralizes hydrogen peroxide produced by the action of SOD

Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings Figure 6.15 - Overview Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings

Glove box

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Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings Table 6.2 Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings

Nitrogen Requirements: Nitrogen fixation

Anabolism often ceases due to insufficient nitrogen needed for proteins and nucleotidesNitrogen acquired from organic and inorganic nutrients; also, all cells recycle nitrogen from amino acids and nucleotidesNitrogen fixation: the reduction of nitrogen gas to ammonia by certain bacteria is essential to life on Earth because nitrogen is made available in a usable form


Other Chemical Requirements

Phosphorus required for phospholipid membranes, DNA, RNA, ATP, and some proteinsSulfur is a component of sulfur-containing amino acids, disulfide bonds critical to tertiary structure of proteins, and in vitamins (thiamin and biotin)Trace elements – usually found in sufficient quantities in tap waterGrowth factors – organic chemicals that cannot be synthesized by certain organisms (vitamins, certain amino acids, purines, pyrimidines, cholesterol, NADH, and heme)


Physical Requirements for Growth

TemperaturepHOsmolarityPressure

Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings Figure 6.4 - Overview Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings Figure 6.5

Categories of organisms by temperature tolerance

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Food spoilage


Cooling rate


Temperature

Effect of temperature on proteins: denaturationEffect of temperature on lipid-containing membranes of cells and organelles

If too low, membranes become rigid and fragileIf too high, membranes become too fluid and cannot contain the cell or organelle


pH

Organisms sensitive to changes in acidity because H+

and OH- interfere with H bonding in proteins and nucleic acidsNeutrophiles - Most bacteria and protozoa grow best around neutral pH (6.5-7.5) Acidophiles – grow best in acidic habitats

Acidic waste products can help preserve foods by preventing further microbial growth

Alkalinophiles live in alkaline soils and water up to pH 11.5


Physical Effects of Water

Microbes require water to dissolve enzymes and nutrients required in metabolismWater is important reactant in many metabolic reactionsMost cells die in absence of water

Some have cell walls that retain waterEndospores and cysts cease most metabolic activity in a dry environment for years

Two physical effects of waterOsmotic pressureHydrostatic pressure


Osmotic Pressure

Hypertonic solutions have greater solute concentrations; cells placed in these solutions will undergo crenation (shriveling of cytoplasm)

This effect helps preserve some foods

Restricts organisms to certain environments

Obligate halophiles – grow in up to 30% saltFacultative halophiles – can tolerate high salt concentrations

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Hydrostatic Pressure

Water exerts pressure in proportion to its depthFor every addition of depth, water pressure increases 1 atm

Barophiles: Organisms that live under extreme pressureTheir membranes and enzymes depend on this pressure to maintain their three-dimensional, functional shape


Ecological Associations: definitions

Organisms live in association with different species, not as pure cultures

Antagonistic relationshipsSynergistic relationshipsSymbiotic relationships

BiofilmsComplex relationships among numerous individualsForm on surfaces often as a result of quorum sensing –communication among bacteria


Culturing Microorganisms

Inoculum introduced into medium (broth or solid)Environmental specimensClinical specimensStored specimens

Culture – refers to act of cultivating microorganisms or the microorganisms that are cultivated


Clinical Sampling

Table 6.3


Obtaining Pure Cultures: COLONIES

Pure cultures are composed of cells arising from a single cell (progenitor)

Progenitor is termed a CFU (colony-forming unit)Aseptic technique is used to prevent contamination of sterile substances or objects

Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings Figure 6.7 - Overview

Colonies

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Isolation techniques: Streak Plate Method

Figure 6.8a

Two common isolation techniques:

Streak platesPour plates


Streak Plate Method

Figure 6.8b

colony


Pour Plate Method

Figure 6.9a Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings

Pour Plate Method showing types of colonies

Figure 6.9b


Culture Media

Majority of prokaryotes have never been grown in culture mediumSix types of general culture media

Defined mediaComplex mediaSelective mediaDifferential mediaAnaerobic mediaTransport media


Media definitions

Defined: know exact chemical compositionComplex: made from animal and plant extracts; exact chemical composition not known

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Defined


Defined 2


Complex media


definitions

Selective: includes substance which inhibits growth of unwanted microbes from mixed sampleEnrichment: encourages growth of wanted organisms from mixture (phenol users from environment)Differential: to distinguish between organisms

Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings Figure 6.10

Differential example: Simmons citrate agar


Selective: includes substance which inhibits growth of unwanted microbes from mixed sample

Acidic media inhibits bacteria

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Differential example: distinguish between organisms using blood agar hemolysis

B hemolysis

A hemolysis

No hemolysis


Differential example: Sugar fermentation

Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings Figure 6.14a-c

MacConkey agar: selective and differential

Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings Table 6.5


Preserving Cultures by temperature

RefrigerationDeep-freezingLyophilization


Binary fission

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Generation time


Arithmetic Versus Logarithmic Growth

Figure 6.18a-b


Phases of Microbial Growth

Figure 6.20 Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings

Measuring Microbial Growth

Direct methodsViable plate countsMembrane filtrationMicroscopic countsElectronic countersMost probable number


Viable Plate Count: steps in the procedure

SampleDilutionPlatingIncubationCounting cfu’sCalculations

Plate count calculations

colonies/ml. plated__________________________________

dilution factor


Viable Plate Count dilutions

Figure 6.21

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Pour plate



Microscopic Counts

Figure 6.23 Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings

Most Probable Number

Figure 6.24

Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings Table 6.6 (1 of 2) Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings Table 6.6 (2 of 2)

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Measuring Microbial Growth

Indirect MethodsMetabolic activityDry weightTurbidity


Turbidity and SpectrophotometricMeasurement

Figure 6.25a


Turbidity and SpectrophotometricMeasurement

Figure 6.25c

bauman mm ch06 for lecture - york college of pennsylvaniafaculty.ycp.edu/~cmathur/micro ch 6.pdf ·...

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