;;Babylon University
College of Medicine
Dept. of Microbiology
Assit. Prof. Dr .Ilham alsaedi
Nutrition and growth of microorganisms
*Nutritional requirements of Bacteria:
Bacteria may require adequate nutrition, optimum PH, temperature and oxygen for multiplication and growth.
Bacteria can be classified into following types on the basis of their ability to synthesize essential metabolites:
(a)Autotrophic:
These are the organisms in which all essential metabolites are synthesized from inorganic source. They use carbon dioxide as the main source of carbon and simple inorganic salts e.g. nitrates, nitrites, ammonium sulphate, to form new protoplasm of the cell.
(b)Heterotrophic:
Here some of the essential metabolites are not synthesized. Organic compounds e.g. Protein, Peptones. Amino acids, Vitamins and growth factors are supplied from outside. Most of the bacteria producing disease in man are heterotrophic. *The other nutritional requirements minerals like, Potassium, Magnesium, Calcium, Iron, Chloride, Zinc, Copper, Iodine these elements are required in small amounts act as factors for essential
A -Purin and Pyrimidines: require for synthesis of nucleic acids.
B- Vitamins: needs as a coenzymes and functional groups of certain enzymes.
Culture media:-
The growth of the bacteria requires a culture media that provides:
a-All the essential nutrients.
b-Proper concentration of salts and ions.
c-Proper PH (Acidity or alkalinity).
d-Gas requirements.
e-Moisture.
f-Temperature.
1-Temperature:
The temperature rang at which an organism grow best is called ((optimum temperature)). In human parasitic organisms, optimum temperature ranges between 30°c and 37°c .
There are three groups of bacteria as regards the temperature of growth:
These are the bacteria growing between 0°c to25°c.They are mostly soil and water bacteria.
(b)Mesophilic:
Some bacteria grow between 20°c and 44°c.This group includes bacteria producing disease.
(c)Thermophilic:
The bacteria that can grows between 50°c and 80°c,so this bacteria will survive after the pasteurization process of milk.
2-Moisture
Water is essential for the growth of bacteria because the various nutrients must be in soluble form or in a form that can be solubilize to
3-Gas requirements: Oxygen
The capacity of bacteria to grow in the presence of oxygen and to utilize depends on possession of a cytochrome oxidase system.
a-Aerobic bacteria:
The bacteria grow only in the presence of oxygen e.g. Pseudomonadace, Bacillus, Sarcina, they require oxygen as hydrogen acceptor.
b-Anaerobes bacteria:
The bacteria that can live in the absence of oxygen.
c-Facultative anaerobes bacteria:
The bacteria that can live with or without oxygen e.g. Vibrio ,Escherichia coli, Salmonella. The micro- aerophilic bacteria grow well with relatively small quantities of oxygen e.g. Hemophilus
d-Obligate anaerobes bacteria:
The bacteria that can multiply only in the absence of oxygen e.g. Bacteroids, Clostridium.
4-PH
Refers to acidity or alkalinity. For most bacteria the optimum PH for growth rang between 6.5 and7.5,some species can grow in very acid or very alkaline conditions.
a-Acidophiles
The bacteria need PH level from 0.5 to grow.
b-Neutrophile
bacteria need PH 5-7.5 to grow, this include most of human pathogens.
c-Alkalinophiles
bacteria that live at PH 7.0 to above 11.5 e.g. soil bacteria.
5-Energy source
Either a source of carbon or other required nutrients.
Bacterial growth:-
Refers to an increase in bacterial cell numbers (multiplication),which results from a programmed increase in the biomass of the bacteria the growth of microorganisms can be measured by:
a- increase of its size but this poor criterion of growth.
b- increase of the number of microorganisms by counting of the living cells(viable all counts) or all cells.
c- by measuring of some components of cell structure such as protein or DNA as an indication of microbial increase (growth) or decrease(death).
Generation time:
The average time required for cell numbers to double. Some bacteria are able to divide as rapidly as once every 12 to 15 minutes, others require to several hours and a few very slow growing bacteria may require more than 24 hours per cell division.
Growth curve:
If a liquid medium is inoculated with microbial cells taken from a culture that has previously been grown under favorable growth conditions, the multiplication follows the typical growth curve shows in the following figure:
Lag phase: characterized by
a- No increase in population.
b- Cells undergo change in chemical composition and increase in size.
c- Increase of intracellular substances.
Logarithmic or exponential phase:
a- Cells double(divide) at constant rate.
b- Mass double at same rate.
c- Metabolic activities constant.
Stationary phase:
a- Accumulation of toxic products and/or exhaustion of nutrients.
b- Some cell die while others grow and divide.
Decline or death phase:
a- die more rapidly than new cells are produced.
b- Death rate accelerates, becoming exponential.
c- Depending on species, all cells die within days to months.
The characteristic growth curve shown above probly only occurs under selected conditions modification do happen in nature and in some circumstances.
Growth of bacteria in an open environment such as soil, water, or even the intestine, generally dose not follow the curve shown above in these circumstances bacterial growth is most often continuous, so that the number of viable microorganisms remain fairly constant over long periods of time.
Laboratory(in vitro) studies of bacteria grown in continuous culture have shown that the organisms grow exponentially in condition of balanced growth and that generation time is determined by the rate at which fresh nutrients are supplied to the culture. continuous culture important for genetic engenering for synthesis of some materials like insulin, vitamins, toxins, etc.
Growth media:-
1-Minimal essential growth medium
*contains only the primary precursor compounds essential for growth.
2-Complex growth medium
*contains most of the organic compound building blocks (e.g. sugars, amino acids, nucleotides) necessary for growth.
*necessary for the growth of fastidious bacteria.
3-Differential growth medium
*contains a combination of nutrients and PH indicators to allow visual distinction of bacteria that grow on or in it.
*is frequently a solid medium on which colonies of particular bacterial species have a distinctive color.
4-Selective growth medium
*contains compounds that prevent the growth of some bacteria while allowing the growth of other bacteria.
*uses certain days or sugars, high salts concentration, or PH to achieve selectivity.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .