bacteriology physiology

Dr Saleh Microbiology 1

Bacterial Physiology

Medical Microbiology L3

Dr. Saleh M Y OTH

PhDMedical Molecular Biotechnology and Infectious Diseases

05/10/2011MBBS-Phase II-IMS - MSU


Bacterial growth

Metabolism is the totality of an organism’s chemical

processes to maintain life


Studying Bacterial Growth

Bacterial Growth - features

The Growth Curve

Bacterial Growth


NUTRITION

What are nutrients that bacteria want?

Bacterial Growth


Nutritional requirements:

1- Macroelements: a- C, N,O, H, S, P. Required in large

amounts; constitute 95% of bacterial cell dry weight,

b- K, Ca, Mg, and Fe found as ions.

Bacterial Growth


Nutritional requirements:

2- Microelements: Mn, Zn, Co, Mo, Ni, Cu are required in trace amounts by most cells =are part of enzymes and cofactors.

3- Growth factors: (cannot synthesize by cell); amino acids, nucleotides (purines and pyrimidines), vitamins.

Bacterial Growth


- Nutritional

- Environmental

- Pure culture

Culture of microorganisms

Culture media

Dependence on oxygen

- Bacterial growth in laboratory conditions

Growth curve

- Microbial metabolism

Factors for microbial growth: Bacterial Growth


Required elements

- C, H, O sources (amino acids, lipids, nucleic acids, sugars)

- N source (amino acids and nucleic acids)

- S source (amino acids)

- P source (nucleic acids, membrane lipids, ATP)

- K, Mg, Ca, Fe (enzyme cofactors, etc.)

Growth factors

Compounds that bacteria require but cannot synthesize

Nutritional factors

Energy sources

-Sunlight for phototrophs

-Oxidation of chemical compounds for chemotrophs

Nutritional diversity (concerning the energy source and carbon source)

-Photoautotrophs

(primary producers)

-Photoheterotrophs

*Chemoautotrophs

*Chemoheterotrophs

Bacterial Growth


1-Nitrogen source; Ammonium (NH4+) is used as the sole N source by most microorganisms. Ammonium could be produced from N2 by nitrogen fixation, or from reduction of nitrate and nitrite.

2-Sulfur source; Most microorganisms can use sulfate (SO4

2-) as the S source.

3-Phosphate source (PO43-) is usually

used as the P source.

Bacterial GrowthNutritional factors


4-Mineral source; For most microorganisms, it is necessary to provide sources of K+, Mg2+, Ca2+, Fe2+, Na+ and Cl-. Many other minerals (e.g., Mn2+ , Mo2+, Co2+, Cu2+ and Zn2+) can be provided in tap water or as contaminants of other medium ingredients.

5-Growth factors; Compounds that bacteria require but cannot synthesize

Bacterial GrowthNutritional factors


1-TemperaturePsychrophile (15oC - 20oC)

Mesophile (30oC - 37oC)

Thermophile (50oC - 60oC)

2-pHNeutrophile (pH 6 - 8)

Acidophile (pH 1-5)

Alkaliphile (pH 9-11)

Environmental factors

3-Oxygen availabilityObligate aerobe (O2)

Obligate anaerobe (CO2)

Facultative anaerobe (O2 /CO2)

Microaerophile (5-10% O2)

4-Water availabilityOsmophile

Halophile

Bacterial Growth


Obligate aerobe

Facultative anaerobe

Obligate anaerobe

Microaerophile1

2

3

4O2

O2 or Co2

Co2Superoxide dismutase


Obtaining a pure culture

A solid medium is required for

obtaining a pure culture of

microorganism.

Agar: an algae extract,

polysaccharide in nature, which

very few bacteria can degrade.

The agar plate contains 1.5%

of agar.

Colony: population of bacterial

cells arising from a single cell.

Cultivating bacteria on a solid medium (bacterial isolation)


Streak-plate method


Pour plate method


Culture of microorganisms

Complex (rich) media

nutrient agar or broth;

blood agar or chocolate agar for more fastidious bacteria.

Chemically defined (minimal media)

Selective media

Inhibitors for organisms other than the one being sought are added.

Culture media Differential media

Substances that certain bacteria change in a recognizable way are added.

Nutrient broth Glucose-salt

Peptone Glucose

Meat extract Dipotassium phosphate

Water Monopotassiumphosphate

Magnesium sulfate

Ammonium sulfate

Calcium chloride

Iron sulfate

Water


MacConkey agar plate

Blood agar plate

Back


Principles of bacterial growth

-Bacteria multiply by

binary fission.

-Microbial growth is

defined as an increase in

the number of cells in a

population.

Bacterial growth curve

Bacterial growth in laboratory conditions

Generation time

E. coli: 20 min

M. tuberculosis: 12-24 h


Bacterial growth curve

Bacterial growth in laboratory conditions


A balance between slow loss of cells through death and the formation of new cells through growth and division.

Bacteria synthesize macromolecules required for multiplication.

The length of lag phase depends on the conditions in the original culture and the medium into which they are transferred.

The doubling time is measured during this period.

The bacteria are most susceptible to antibiotics during this time. Bacteria stop growing due to decrease of nutrients and O2 supply, and accumulation of toxic metabolites.

The bacteria die off rapidly, the curve turns downward, and the last cell in the population soon dies.


Assimulation (anabolism): energy-requiring

Dissimulation (catabolism): energy-acquiring

Bacterial Metabolism

Focal metabolites: metabolic intermediates that link

anabolic and catabolic pathways.

Glycolysis

Pentose phosphate pathway

TCA cycle

Respiration (aerobic and anaerobic)

Fermentation


Saccharomycetes

E. coliClostridium

Propionebacterium Enterobacter

StreptococcusLactobacillus


Increased CO2

Candle jar; CO2 incubator

Microaerophilic

Culture methodsAnaerobic

Anaerobic jar; anaerobic chamber; reducing agents


Enrichment culturesIsolating an organism from natural sources


Maintaining stock cultures

Agar slant

Store agar slant cultures in a

refrigerator.

Stock at –70 to -80 oC

Store a pure culture in the

presence of 17% glycerol.

Lyophilization (freeze drying)

Dry a pure culture with a

lyophilizer. This can be stored

at room temperature for years.


Direct cell count

Count under a microscope;

cell-counting instrument

Measuring biomass

Turbidity;

total weight;

chemical constituents

Viable cell count

Plate counts(MPN);

membrane filtration;

Detecting cell products

Methods to detect and measure bacterial growth


Overview of Medically Important Bacteria

Rickettsia Chlamydia Mycoplasma*

Clostridia

Actinomycetes

Obligate IntracellularExtracellular & Facultative

Gram-positive Gram-negative Mycobacteria Spirochetes

Cocci Bacilli

StaphylococciStreptococciEnterococci

ListeriaBacillusCorynebacteria

Cocci and coccobacilli

Bacilli

Haemophilus

Bordetella

Neisseria

Enterobacteriaceae

Pseudomonads

Legionella

Campylobacter

Helicobacter

Borrelia

Leptospira

Treponema

Brucella

Francisella

Pasteurella

Aerobes StrictAnaerobes

Vibrio


Topics for reading:

Using of Microscope and its parts

Classification of Bacteria

Bacterial structure

Bacterial multiplication

Bacterial genetic


Topics for reading:

Catabolism and anabolism

ATP Generation and energy conservation

Fermentation


Thank you

Study QuestionsBesides chemical nutrients, what are 4 other factors you would consider when trying to grow a bacterium for the first time?

Why do you need to sterilize bacterial media? What are some ways you could do this? What would happen if you didn’t sterilize the media?

What are the four phases of growth curve? What is happening in each?

bacteriology physiology

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