Microbial growth and nutritional requirements fileMicrobial growth and nutritional requirements Microbiology & Immunology Microbial growth and nutritional requirements • Microorganisms

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Microbial growth and nutritional requirements

Microbiology & Immunology

Microbial growth and nutritional requirements

• Microorganisms use chemicals called nutrients for growth and development.

• They need these nutrients to build molecules and cellular structures.

• The most important nutrients are carbon, hydrogen, nitrogen, and oxygen.

• Microorganisms get their nutrients from sources in their environment. When these microorganisms obtain their nutrients by living on or in other organisms, they can cause disease in that organism by interfering with their host’s nutrition, metabolism, and, thus disrupting their host’s homeostasis, the steady state of an organism.

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Two nutritional types microorganisms :1- autotrophs

• Organisms can be classified in two groups depending on how they feed themselves.

• Organisms that use carbon dioxide (CO2) as their source of carbon are called autotrophs. These organisms “feed themselves,” auto- meaning “self” and -troph meaning “nutrition.” Autotrophsmake organic compounds from CO2.

All categories• Source of carbon:

1. An autotroph can derive its carbon from carbon dioxide.2. A heterotroph must use one or more organic compounds as its

source of carbon.• Source of energy:

1. A chemotroph obtains its energy from chemical compounds. 2. A phototroph uses light as its source of energy.

• Source of electron:1. A lithotroph is an organism that uses inorganic molecules as a

source of electrons. 2. An organotroph uses organic molecules for the same purpose.

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Two nutritional types microorganisms :1- heterotrophs

• Organisms that obtain carbon from organic nutrients like proteins, carbohydrate, amino acids, and fatty acids are called heterotrophs.

• Heterotrophic organisms acquire or feed on organic compounds from other organisms.

Two categories of organisms (by the source of energy)

• Organisms can also be categorized according to whether they use chemicals or light as a source of energy.

• Organisms that acquire energy from redox reactions involving inorganic and organic chemicals are called chemotrophs. Organisms that use light as their energy source are called phototrophs.

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Categories by the source of electron

• There is one final subdivision of nutritional categories in microorganisms!

• Whether organisms are chemotrophs or phototrophs, they need a molecule to act as a source of electrons (reducing power) to drive their energy generating systems.

• Those able to use an inorganic electron donor such as H2O, H2S or ammonia are called lithotrophs, while those requiring an organic molecule to fulfill the role are organotrophs.

• Most (but not all) microorganisms are either photolithotrophic autotrophs (algae, blue-greens) or chemo-organotrophic heterotrophs (most bacteria).

All categories - summary• Source of carbon:

1. An autotroph can derive its carbon from carbon dioxide.2. A heterotroph must use one or more organic compounds as its

source of carbon.• Source of energy:

1. A chemotroph obtains its energy from chemical compounds. 2. A phototroph uses light as its source of energy.

• Source of electron:1. A lithotroph is an organism that uses inorganic molecules as a

source of electrons. 2. An organotroph uses organic molecules for the same purpose.

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All categories• Source of carbon:

1. An autotroph can derive its carbon from carbon dioxide.2. A heterotroph must use one or more organic compounds as its

source of carbon.• Source of energy:

1. A chemotroph obtains its energy from chemical compounds. 2. A phototroph uses light as its source of energy.

• Source of electron:1. A lithotroph is an organism that uses inorganic molecules as a

source of electrons. 2. An organotroph uses organic molecules for the same purpose.

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CARBON (C)

• Carbon is one of the most important requirements for microbial growth.

• Carbon is the backbone of living matter. Some organisms, such a photoautotrophs, get carbon from carbon dioxide (CO2).

OXYGEN (O)1. Microorganisms that use oxygen produce more energy from nutrients than

microorganisms that do not use oxygen. These organisms that require oxygen are called obligate aerobes.

• Oxygen is essential for obligate aerobes because it serves as a final electron acceptor in the electron transport chain, which produces most of the ATP in these organisms. An example of an obligate aerobe is Micrococcus.

2. Some organisms can use oxygen when it is present, but can continue togrow by using fermentation or anaerobic respiration when oxygen is not available.

• These organisms are called facultative anaerobes. An example of a facultative anaerobe is E. coli bacteria, which is found in the large intestine ofvertebrates, such as humans.

3. Some bacteria cannot use molecular oxygen and can even be harmed by it.• Examples include Clostridium botulinum, the bacterium that causes

botulism, and Clostridium tetani, the bacterium that causes tetanus. These organisms are called obligate anaerobes. Molecular oxygen (O2) is a poisonous gas to obligate anaerobes.

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Oxygen

Nitrogen• Nitrogen is needed for the synthesis of proteins

and nucleic acids, as well as for important molecules such as ATP.

• Microorganisms range in their demands for nitrogen from those that are able to assimilate (‘fix’) gaseous nitrogen (N2) to those that requireall 20 amino acids to be provided preformed.

• Between these two extremes come species that are able to assimilate nitrogen from an inorganic source such as nitrate, and those that utilise ammonium salts or urea as a nitrogen source.

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Other elements• Sulphur (S) is required for the synthesis of proteins

and vitamins, and in some types is involved in cellular respiration and photosynthesis. It may be derived from sulphurcontaining amino acids (methionine, cysteine), sulphates and sulphides.

• Phosphorus (P) is taken up as inorganic phosphate, and is incorporated in this form into nucleic acids and phospholipids, as well as other molecules such as ATP.

• Metals such as copper, iron and magnesium are required as cofactors in enzyme reactions.

• A cofactor is a nonprotein component of an enzyme (often a metal ion) essential for its normal functioning.

Chemical Requirements

Macro & Micro Elements

C HOPKINS CaFe Mg NaCl

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Culture Media• A culture medium is nutrient material prepared in the

laboratory for the growth of microorganisms. Microorganisms that grow in size and number on a culture medium are referred to as a culture.

• In order to use a culture medium must be sterile, meaning that it contains no living organisms. This is important because we only want microorganisms that we add to grow and reproduce, not others. We must have the proper nutrients, pH, moisture, and oxygen levels (or no oxygen) for a specific microorganism to grow.

Culture Media• The most popular and widely used medium used in

microbiology laboratories is the solidifying agent agar. Agar is a complex polysaccharide derived from red algae. Very few microorganisms can degrade agar, so it usually remains in a solid form. Agar media are usually contained in test tubes or Petri dishes. The test tubes are held at a slant and are allowed to solidify on an angle, called a slant. A slant increases the surface area for organism growth. The shallow dishes with lids to prevent contamination are called Petri dishes. Petri dishes are named after their inventor, Julius Petri, who in 1887 first poured agar into glass dishes.

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Types of culture mediaClassification # 1• Chemically defined media• Complex MediaClassification # 2a. Enriched mediab. Selective mediac. Deferential mediad. Propagation media

GROWING BACTERIAL CULTURES

• Bacteria normally reproduce by a process called binary fission:

• 1. The cell elongates and chromosomal DNA is replicated.

• 2. The cell wall and cell membrane pinch inward and begin to divide.

• 3. The pinched parts of the cell wall meet, forming a cross wall completely around the divided DNA.

• 4. The cells separate into two individual cells.

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GENERATION TIME

• The generation time is the amount of time needed for a cell to divide.

• This varies among organisms and depends upon the environment they are in and the temperature of their environment. Some bacteria have a generation time of 24 hours, although the generation time of most bacteria is between 1 to 3 hours.

• Bacterial cells grow at an enormous rate. For example, with binary fission, bacteria can double every 20 minutes. In 30 generations of bacteria (10 hours), the number could reach one billion. It is difficult to graph population changes of this magnitude using arithmetic numbers, so logarithmic scales are used to graph bacterial growth.

Growth of m/o

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Phases of Growth

Growth curve

• The growth cycle includes :

• lag phase• exponential phase or

log (logarithmic) phase

• stationary phase, and• a death phase.

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THE LAG PHASE

• In the lag phase there is little or no cell division. This phase can last from one hour to several days. Here the microbial population is involved in intense metabolic activity involving DNA and enzyme synthesis.

• This is like a factory “shutting down” for two weeks in the summer for renovations. New equipment is replacing old and employees are working, but no product is being turned out.

THE LOG PHASE

• In the log phase, cells begin to divide and enter a period of growth or logarithmic increase. This is the time when cells are the most active metabolically. This is the time when the product of the factory must be produced in an efficient matter.

• In this phase, however, microorganisms are very sensitive to adverse conditions of their environment.

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THE STATIONARY PHASE

• This phase is one of equilibrium. The growth rate slows, the number of dead microorganisms equals the number of new microorganisms, and the population stabilizes. The metabolic activities of individual cells that survive will slowdown.

• The reasons why the growth of the organisms stops is possibly that the nutrients have been used up, waste products have accumulated, and harmful changes in the pH of the organisms environment have occurred.

THE DEATH PHASE

• Here the number of dead cells exceeds the number of new cells. This phase continues until the population is diminished or dies out entirely.

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Phases of growth

Factors affecting microbial growth

• Temperature• Microorganisms as a group are able to grow over a wide

range of temperatures, from around freezing to above boiling point. For any organism, the minimum and maximum growth temperatures define the range over which growth is possible;

• Optimum t is typically about 25–30 ◦C. Growth is slower at low temperatures because enzymes work lessefficiently and also because lipids tend to harden and there is a loss of membrane fluidity.

• Growth rates increase with temperature until the optimum temperature is reached, then the rate falls again

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Temperature

Types of microorganisms

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pH• Microorganisms are strongly influenced by the

pH of their surroundings. As with temperature, we can define minimum, optimum and maximum values for growth of a particular type. The pH range (between minimum and maximum values) is greater in fungi than it is in bacteria.

• Most microorganisms grow best aroundneutrality (pH 7).

• Many bacteria prefer slightly alkaline conditions but relatively few are tolerant of acid conditions, and fewer still are acidophilic.

pH

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Control of microbial growth• Physical Methods of Control:• Dry heat kills microorganisms by reacting with and

oxidizing their proteins. Dry heat can be used in incineration devices, such as the Bunsen burner or the hot-air oven. In the hot-air oven, a temperature of about 170°C for two hours will bring about sterilization.

• Moist heat is used to kill microorganisms in such things as boiling water. Most vegetating microorganisms are killed within two or three minutes, but over two or three hours may be required for destruction of bacterial spores. In moist heat, the microbial proteins undergo denaturation, a process in which the three-dimensional form of the protein reverts to a two-dimensional form, and the protein breaks down. (Autoclavation)

Autoclave• Moist heat is used in the autoclave, a high-

pressure device in which steam is superheated. Steam at 100°C is placed under a pressure of 15 pounds per square inch, increasing the temperature to 121°C. At this temperature, the time required to achieve sterilization is about 15 minutes. The autoclave is the standard instrument for preparing microbial media and for sterilizing instruments such as syringes, hospital garb, blankets, intravenous solutions, and myriad other items.

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Another Heating Method• An alternative heating method is tyndallization,

also called intermittent sterilization. Liquids and other items are subjected to free flowing steam for 30 minutes on each of three successive days. During the first day, all vegetating microorganisms, except spores, are killed. In the overnight period, the spores germinate, and they are killed by the steam on the second day. The last few remaining spores germinate on the second evening and are killed on the third day.

Irradiation• Sterilisation by irradiation• Certain types of irradiation are used to control

the growth of microorganisms. These include both ionising and non-ionising radiation.

• The most widely used form of non-ionising radiation is ultraviolet (UV) light.Wavelengths around 260nm are used because these are absorbed by the purine and pyrimidinecomponents of nucleic acids, as well as certain aromatic amino acids in proteins. The absorbed energy causes a rupture of the chemical bonds, so that normal cellular function is impaired.

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Irradiation

• Ionising radiations have a shorter wavelength and much higher energy, giving them greater penetrating powers. The effect of ionising radiations is due to the production of highly reactive free radicals, which disrupt the structure of macromolecules such as DNA and proteins. Surgical supplies such as syringes, catheters and rubber gloves are commonly sterilised employing gamma (γ ) rays from the isotope cobalt 60 (60Co).

Filtration

• Many liquids such as solutions of antibiotics or certain components of culture media become chemically altered at high temperatures, so the use of any of the heat regimes described above is not appropriate.

• Rather than killing the microorganisms, an alternative approach is simply to isolate them.

• This can be done for liquids and gases by• passing them through filters of an appropriate

pore size.

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Filtration (membrane filter)

Chemical Methods of Control

• The growth of a microorganism can be controlled through the use of a chemicalagent. A chemical agent is a chemical that either inhibits or enhances the growth of a microorganism.

• Commonly used chemical agents include phenols, phenolics, glutaraldehyde, and formaldehyde.

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Action of Antimicrobial Agents

• There are two categories that chemical and physical antimicrobial agents fall into:

1. those that affect the cell walls or cytoplasmic membranes of the microorganism and

2. those that affect cellular metabolism and reproduction.

Phenols, alcohols, halogens, heavy metals

• Phenols are compounds derived from pheno (carbolic acid) molecules. Phenolics disrupt the plasma by denaturing proteins; they also disrupt the plasma membrane of the cell.

• Alcohols are effective against bacterial fungi and viruses. However, they, are not effective against fungal spores or bacterial endospores.

• Halogens are nonmetallic, highly resistive chemical elements. Halogens are effective against vegetative bacterial cells, fungal cells, fungal spores, protozoan cysts, and many viruses. (chlorine, iodine)

• Arsenic, zinc, mercury, silver, nickel, and copper are called heavy metals due to their high molecular weights. They inhibit microbial growth because they denature enzymes and alter the three-dimensional shapes of proteins that inhibit or eliminate the protein’s function. Heavy metals are bacteriostatic and fungistaticagents.

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Soaps and detergents.

• Soaps and detergents decrease the surface tension between microorganisms and surfaces, and thereby help cleanse the surface.

• Soaps emulsify the oily film on the body surface, carrying the oils, debris, and microorganisms away in a degermingaction.

Antibiotics

• Various families of antibiotics are used for various types of microorganisms to achieve control and assist body defenses during times of infection.

• Antibiotics are products of microorganisms that react with and inhibit the growth of other microorganisms.

• An antibiotic should be selectively toxic to pathogenic microorganisms, should not incite an allergic response in the body, should not upset the normal microbialpopulation of various body sites, and should not foster the development of drug resistance.