Microbial Growth

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•Bacterial cell is composed of:

•Water

•Organic

•Protein

•Sugars

•Lipids

•Nucleic acid

Microbial nutrition

•Macronutrients – required in large quantities; play principal roles in cell structure & metabolism

–proteins, carbohydrates

•Micronutrients or trace elements – required in small amounts; involved in enzyme function & maintenance of protein structure

–manganese, zinc, nickel

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Bacterial Nutrition and Growth

Classification based on their source of carbon

•1 .Autotrophs •2 .Heterotrophs :saprophytes ; parasites

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Bacterial Nutrional Modes

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Requirements for Microbial Growth

• Physical Requirements

• Chemical Requirements

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The Requirements for Growth •The requirements for microbial growth can be

divided into two main categories:

physical and chemical . Physical aspects include

•temperature, pH, and osmotic pressure .

Chemical requirements• include sources of carbon, nitrogen, sulfur,

phosphorus, oxygen, trace elements, and organic growth factors . 7

•Temperature•Optimum temperature – promotes the fastest rate of

growth and metabolism

•Mesophilic forms （ 30-37C ℃ ） include all human pathogens and opportunists.

•pH

• Many grow best at neutral pH (Most bacteria grow in the range of pH 6.5-7.5

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Requirements for Microbial Growth

Physical requirements

The composition of bacterial cell is 80-90% water .

3 -Osmotic Pressure

In high osmotic pressures solution (hypertonic), the water move from inside bacterial cell to outside

•The growth of the cell is inhibited as the plasma membrane pulls away from the cell wall.

Thus, addition of salts or other solutes to solution can be used to preserve food.

•Loss of water from the cell results in Plasmolysis.

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Oxygen Requirements

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for growth Required CO2

•N. meningitidis

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N. Gonorrhoeae

Requirements for Microbial Growth chemical requirements

#Carbon :

•Chemoheterotrophs: organic matter

•Chemooutotrophs , photoutotrophs from Co2.

#Nitrogen _Sulfur _and phosphorous

#Trace Elements: iron _ copper _ and zinc

#Oxygen:13

•Bacterial growth

•&

•reproduction

Binary fission in bacteria

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•Bacterial culture

Culture media

•Any material prepared in the laboratory for the growth of bacteria and usually in test tubes or petri dishes

•Culture = microbes that grow & multiply in or on a culture medium

Culture Media

Culture medium InoculumCultureSterile

Types of culture mediaSolid (agar)/semisolid/liquid (broth)

Agar; liquid down to 50C solidify at 45 C, not consumed by bacteria as nutrient.

Agar solid media are poured in plates(Petri dish) or tubes. In tubes they are poured either as slants or deeps.

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Culture media

•Chemically defined media = is one in which the exact chemical composition is known (energy source , carbon , nitrogen , sulfur , phosphorus , growth factors)

•Complex media = in which the exact chemical composition varies slightly from batch to batch (protein added)

Culture media

•Differential media = used to distinguish among different kinds of bacteria

Culture media

•Selective media = allow the growth of only one kind of bacteria & prevent the growth of other by the addition f certain salts & dyes

Culture media

•Enrichment media = is used to encourage the growth of particular bacteria in mixed culture

•Obtaining pure culture

Streak-Plate Method

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•Inoculated culture media must be incubated at 37C = incubator

•* some bacteria require an increased CO2 concentration = CO2 incubator or candle jars can be used

•*some bacteria need anaerobic condition to grow ( remove O2)

Bacterial colonies on several differential media.  

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The Growth of Bacterial Cultures

•Binary fission

•Generation time

•Phases of Growth

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Growth curve.1Lag phase – “flat” period of adjustment, enlargement;

little growth

.2Exponential growth phase – a period of maximum growth will continue as long as cells have adequate nutrients & a favorable environment

.3Stationary phase – rate of cell growth equals rate of cell death cause by depleted nutrients & O2, excretion of organic acids & pollutants

.4Death phase – as limiting factors intensify, cells die exponentially in their own wastes

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Generation time

•time for bacterial mass to double

•Example

100 bacteria present at time 0

If generation time is 2 hr

After 8 hr mass = 100 x 24

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Obtaining Pure Culture

•Colony=is a visible mass of microbial cell that theoretically arose from one cell

•Streak plate technique

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The streak plate method for isolating pure bacterial cultures.  

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First Term Exam.Good Luck