GROWTH AND NUTRITION OF BACTERIA

Bacterial physiology and growth factors

Santosh Yadav M.Sc. Clinical Microbiology Dept. of MicrobiologyInstitute of MedicineTribhuvan Univarsity Teaching Hospital, Nepal1

Santosh yadavNutrition requirementsBacteria has same general chemical pattern as the cells of other organism.Principal constituent of the bacterial cell is water, proteins , polysaccharides , lipids, nucleic acids, mucopeptides and other low molecular weigth compounds.For growth and muliplication of bacteria,the minimum requirements areWater,Source of carbon and energy,Source of nitrogen,andSome inorganic salts.2

Santosh yadavMacronutrients

Microorganisms require some elements in large quantities, because they are used to construct carbohydrates, lipids, proteins, and nucleic acids.95% or more of cell dry weight is made up of a few major elements: C ,O , H, N , S and P.Required in large amount. 3

Santosh yadavTrace Elements

Microbes require very small amounts of other mineral elements, such as Fe , Cu, Mo , Zn, etc . Most are essential for activity of certain enzymes, usually as cofactors.

Eg- Mg for Hexokinase , Ni for urease, Fe for cytochrome oxidase , etc

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Ref:-Microbiology by Anderson and Neseter.

Santosh yadavGrowth Factors Organic compounds required in minute quantities and are not synthesized by bacteria, also called bacterial vitamins.Such as amino acids, vitamins, purines, and pyrimidinesEgNeisseria spp require at least 40 additional ingredients, including 7 vitamins and all of the 20 amino acids.6

Santosh yadavEnergy sourceOrganism derive energy either from sunlight or from oxidation of chemical compounds.Phototrophs, and Chemotrophs.

Carbon source Autotroph:- can synthesize all their organic compounds.Heterotroph :- can not synthesize and depends on preformed organic compounds.

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Santosh yadavBactrial GrowthIt is an increase in number of population rather than in size.

Bacteria divide by binary fission.

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Santosh yadavBinary fission

9Ref:-Microbiology, Nester

Santosh yadavGeneration time

Time required for a bacterium to give rise to 2 daughter cells under optimum conditions .Also called population doubling time.Escherichia coli 20 mins.Mycobacterium tuberculosis 20 hrs.M.leprae 20 days.10

Santosh yadavGrowth curve

11Ref:-Microbiology, Nester

Santosh yadavLag phase Phase of adaptation in new medium.Necessary enzymes and metabolites are built up.Bacterial cell attain maximum size and is critical stage for multiplication.Length depends on generation time of bacteria, size of inoculum, quantity of culture medium, environmental factors, etcAverage time:- 2-6 hours.12

Santosh yadav Log or exponential phaseCell division occurs at maximum rate and number increases exponentially with time.Becomes smaller in size.Bacteria are most sensitive to antimicrobial substances.13

Santosh yadavStationary phase Growth ceases due to exhaustion of nutrients, accumulation of of toxic metabolites and lowering of pH.Produce secondary metabolites.Frequently gram variable and stain irregularly.Sporulation occurs.

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Santosh yadavDeath or decline phase

Cells begin to die due to cessation of growth, accmulation of toxic products, autolytic and heterolytic enzymes.Rapid fall in viable count.Some cells remain survive at the expense of nutrients released from cell death.15

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Factors affecting bacterial growth16

Santosh yadavWaterAbout 80% of bacterial cell is water hence it is essential requirement.Vehicle for entry of nutrients and elimination of waste products.Participate in metabolic reactions17

Santosh yadavTemperatureMajor environmental factor controlling growth.Minimum:- below which growth ceases.Optimum:- at which maximum growth occur.Maximum:- above which growth ceases.

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Santosh yadavClassification by tempr. requirement Psychrophiles:- best grow at low temprature (-5 -15C)

Produce enzymes that functions optimally in cold.

eg. Yersinia enterocolitica , Listeria monocytogens , Pseudomonas fluorescens.

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Santosh yadavMesophiles

Temprature range for growth 25-45C.Optimum growth temp 37C.Are mostly pathogenic bacteria.Eg..Escherichia coli , staphylococcus aureus , etc.20

Santosh yadavThermophilesRange 45-70CContain heat stable enzymes and proteins..Eg..Bacillus sterothermophilus.Hyoerthermophiles- grow at temp above 70C.EgThermotoga, Methanopyrus.21

Santosh yadavOxygenDifferent bacteria have different oxygen requirement.

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Santosh yadavClassification based on O2 requirementObligate aerobes:-Grow only in presence of oxygen.Eg.. Pseudomonas , Brucella , Mycobacteria , Nocardia spp etc. Facultative anerobes:- prefer aerobic condition but can grow without oxygen.Eg Staphylococcus spp, Corynebacterium sps, Salmonella spp, Shigella spp , Escherichia coli, etcMicroaerophiles:- Are aerobes but require little of oxygen for growth. Eg Campylobacter jejuni, etc.

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Obligate anaerobes:- Grow only in absence of oxygen and oxygen is lethal for them.EgClostridium sps, Bacteroides sps, etc...Aerotolerent anaerobes:-Do not utilize oxygen , but can tolerate low amount of oxygenEg..Lactobacilli , anaerobic streptococci , etc24

Santosh yadavCarbondioxide( CO2)Small amount of CO2 is required by all bacteria.

Some organisms grow best at higher CO2 tension and are called capnophillic. Eg..Brucella sps , gonococcus, meningococcus.25

Santosh yadavHydrogen ion concentration(pH)

Most bacteria grow at neutral or slightly alkaline pH.

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Santosh yadavClassificationAcidophiles:- grow at acidic pH.pH range ( < 5.0). Eg..Lactobacillus spsNeutrophiles:- pH range ( > 5.0 and 8 ).Eg.. Vibrio cholera ,

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Santosh yadavOsmotic pressureBacteria can withstand wide range of external osmotic pressure because of protective cellwall.

0.5% of NaCl is added in most culture medium to maintain suitable environment.

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Santosh yadav contdSome bacteria grow at high pressure , i.e. 400-500 atm (mostly in deep sea) and are called barophiles.

Eg..Photobacterium shewanella29

Santosh yadavSymbiosis and antagonismWhen growth of one organism fascilitates another (symbiosis).

E.g. Staphylococcus aureus helping the growth of Hemophilus influenza.

When growth of one organism hampering another ( antagonism).

Eg..Pseudomonas aeruginosa hampering the growth of gonococcus and anthrax bacilli.

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