Production of antibiotics
Encyclopedia
The production of antibiotics has been widespread since the pioneering efforts of Florey
and Chain
in 1938. The importance of antibiotics to medicine
has led to much research into their discovery and production.
Despite the wide variety of known antibiotics, less than 1% of antimicrobial agents have medical or commercial value
. For example, whereas penicillin
has a high therapeutic index
as it does not generally affect human cells, this is not so for many antibiotics. Other antibiotics simply lack advantage over those already in use, or have no other practical applications.
Useful antibiotics are often discovered using a screening process. To conduct such a screen, isolates of many different microorganism
s are cultured
and then tested for production of diffusible
products that inhibit the growth of test organisms. Most antibiotics identified in such a screen are already known and must therefore be disregarded. The remainder must be tested for their selective toxicities and therapeutic activities, and the best candidates can be examined and possibly. penicillin.
A more modern version of this approach is a rational design program. This involves screening directed towards finding new natural products that inhibit
a specific target, such as an enzyme
only found in the target pathogen, rather than tests to show general inhibition of a culture.
, where the source microorganism is grown in large containers (100,000–150,000 liters or more) containing a liquid growth medium
. Oxygen concentration, temperature, pH
and nutrient
levels must be optimal, and are closely monitored and adjusted if necessary. As antibiotics are secondary metabolite
s, the population size must be controlled very carefully to ensure that maximum yield is obtained before the cells die. Once the process is complete, the antibiotic must be extracted and purified
to a crystalline
product. This is simpler to achieve if the antibiotic is soluble in organic solvent. Otherwise it must first be removed by ion exchange
, adsorption
or chemical precipitation
.
. This is because species are often genetically modified
to yield the maximum amounts of antibiotics. Mutation
is often used, and is encouraged by introducing mutagen
s such as ultraviolet radiation, x-rays or certain chemicals. Selection and further reproduction of the higher yielding strains over many generations can raise yields by 20-fold or more.
Another technique used to increase yields is gene
amplification, where copies of genes coding for enzymes involved in the antibiotic production can be inserted back into a cell, via vectors such as plasmid
s. This process must be closely linked with retesting of antibiotic production and effectiveness.
Howard Walter Florey
Howard Walter Florey, Baron Florey OM FRS was an Australian pharmacologist and pathologist who shared the Nobel Prize in Physiology or Medicine in 1945 with Sir Ernst Boris Chain and Sir Alexander Fleming for his role in the making of penicillin. Florey's discoveries are estimated to have saved...
and Chain
Ernst Boris Chain
Sir Ernst Boris Chain was a German-born British biochemist, and a 1945 co-recipient of the Nobel Prize for Physiology or Medicine for his work on penicillin.-Biography:...
in 1938. The importance of antibiotics to medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
has led to much research into their discovery and production.
Identifying useful antibiotics
Value (economics)
An economic value is the worth of a good or service as determined by the market.The economic value of a good or service has puzzled economists since the beginning of the discipline. First, economists tried to estimate the value of a good to an individual alone, and extend that definition to goods...
. For example, whereas penicillin
Penicillin
Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....
has a high therapeutic index
Therapeutic index
The therapeutic index is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes death or toxicity ....
as it does not generally affect human cells, this is not so for many antibiotics. Other antibiotics simply lack advantage over those already in use, or have no other practical applications.
Useful antibiotics are often discovered using a screening process. To conduct such a screen, isolates of many different microorganism
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s are cultured
Microbiological culture
A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions. Microbial cultures are used to determine the type of organism, its abundance in the sample being tested,...
and then tested for production of diffusible
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
products that inhibit the growth of test organisms. Most antibiotics identified in such a screen are already known and must therefore be disregarded. The remainder must be tested for their selective toxicities and therapeutic activities, and the best candidates can be examined and possibly. penicillin.
A more modern version of this approach is a rational design program. This involves screening directed towards finding new natural products that inhibit
Enzyme inhibitor
An enzyme inhibitor is a molecule that binds to enzymes and decreases their activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors. They are also used as herbicides and pesticides...
a specific target, such as an enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
only found in the target pathogen, rather than tests to show general inhibition of a culture.
Industrial production techniques
Antibiotics are produced industrially by a process of fermentationIndustrial fermentation
Industrial fermentation is the intentional use of fermentation by microorganisms such as bacteria and fungi to make products useful to humans. Fermented products have applications as food as well as in general industry.- Food fermentation :...
, where the source microorganism is grown in large containers (100,000–150,000 liters or more) containing a liquid growth medium
Growth medium
A growth medium or culture medium is a liquid or gel designed to support the growth of microorganisms or cells, or small plants like the moss Physcomitrella patens.There are different types of media for growing different types of cells....
. Oxygen concentration, temperature, pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
and nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
levels must be optimal, and are closely monitored and adjusted if necessary. As antibiotics are secondary metabolite
Secondary metabolite
Secondary metabolites are organic compounds that are not directly involved in the normal growth, development, or reproduction of an organism. Unlike primary metabolites, absence of secondary metabolities does not result in immediate death, but rather in long-term impairment of the organism's...
s, the population size must be controlled very carefully to ensure that maximum yield is obtained before the cells die. Once the process is complete, the antibiotic must be extracted and purified
Purification
Purification is the process of rendering something pure, i.e. clean of foreign elements and/or pollution, and may refer to:* List of purification methods in chemistry* Water purification** Organisms used in water purification...
to a crystalline
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
product. This is simpler to achieve if the antibiotic is soluble in organic solvent. Otherwise it must first be removed by ion exchange
Ion exchange
Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion...
, adsorption
Adsorption
Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...
or chemical precipitation
Precipitation (chemistry)
Precipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...
.
Strains used for production
Microorganisms used in fermentation are rarely identical to the wild typeWild type
Wild type refers to the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard, "normal" allele at a locus, in contrast to that produced by a non-standard, "mutant" allele...
. This is because species are often genetically modified
Genetically modified organism
A genetically modified organism or genetically engineered organism is an organism whose genetic material has been altered using genetic engineering techniques. These techniques, generally known as recombinant DNA technology, use DNA molecules from different sources, which are combined into one...
to yield the maximum amounts of antibiotics. Mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
is often used, and is encouraged by introducing mutagen
Mutagen
In genetics, a mutagen is a physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level. As many mutations cause cancer, mutagens are therefore also likely to be carcinogens...
s such as ultraviolet radiation, x-rays or certain chemicals. Selection and further reproduction of the higher yielding strains over many generations can raise yields by 20-fold or more.
Another technique used to increase yields is gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
amplification, where copies of genes coding for enzymes involved in the antibiotic production can be inserted back into a cell, via vectors such as plasmid
Plasmid
In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...
s. This process must be closely linked with retesting of antibiotic production and effectiveness.