<< Chapter < Page Chapter >> Page >

Learning objectives

  • Identify and describe culture media for the growth of bacteria, including examples of all-purpose media, enriched, selective, differential, defined, and enrichment media

The study of microorganisms is greatly facilitated if we are able to culture them, that is, to keep reproducing populations alive under laboratory conditions. Culturing many microorganisms is challenging because of highly specific nutritional and environmental requirements and the diversity of these requirements among different species.

Nutritional requirements

The number of available media to grow bacteria is considerable. Some media are considered general all-purpose media and support growth of a large variety of organisms. A prime example of an all-purpose medium is tryptic soy broth (TSB) . Specialized media are used in the identification of bacteria and are supplemented with dyes, pH indicators, or antibiotics. One type, enriched media , contains growth factors, vitamins, and other essential nutrients to promote the growth of fastidious organisms , organisms that cannot make certain nutrients and require them to be added to the medium. When the complete chemical composition of a medium is known, it is called a chemically defined medium . For example, in EZ medium , all individual chemical components are identified and the exact amounts of each is known. In complex media , which contain extracts and digests of yeasts, meat, or plants, the precise chemical composition of the medium is not known. Amounts of individual components are undetermined and variable. Nutrient broth, tryptic soy broth, and brain heart infusion , are all examples of complex media.

Media that inhibit the growth of unwanted microorganisms and support the growth of the organism of interest by supplying nutrients and reducing competition are called selective media . An example of a selective medium is MacConkey agar . It contains bile salts and crystal violet, which interfere with the growth of many gram-positive bacteria and favor the growth of gram-negative bacteria , particularly the Enterobacteriaceae . These species are commonly named enterics, reside in the intestine, and are adapted to the presence of bile salts. The enrichment culture s foster the preferential growth of a desired microorganism that represents a fraction of the organisms present in an inoculum. For example, if we want to isolate bacteria that break down crude oil, hydrocarbonoclastic bacteria , sequential subculturing in a medium that supplies carbon only in the form of crude oil will enrich the cultures with oil-eating bacteria. The differential media make it easy to distinguish colonies of different bacteria by a change in the color of the colonies or the color of the medium. Color changes are the result of end products created by interaction of bacterial enzymes with differential substrates in the medium or, in the case of hemolytic reactions, the lysis of red blood cells in the medium. In [link] , the differential fermentation of lactose can be observed on MacConkey agar. The lactose fermenters produce acid, which turns the medium and the colonies of strong fermenters hot pink. The medium is supplemented with the pH indicator neutral red, which turns to hot pink at low pH. Selective and differential media can be combined and play an important role in the identification of bacteria by biochemical methods.

Questions & Answers

what is arabinose operon and it's stucture
Pooja Reply
The L-arabinose operon, also called the ara or araBAD operon, is an operon required for the breakdown of the five-carbon sugar, L-arabinose, in Escherichia coli
kya hum operon ko divide kar skate hain
reactions if viruses to physical and chemical agents?
All viruses contain the following two components: 1) a nucleic acid genome and 2) a protein capsid that covers the genome. Together this is called the nucleocapsid. In addition, many animal viruses contain a 3) lipid envelope. The entire intact virus is called the virion.
assume you have performed a gram stain on a sample of pus from a patients urethra. you see red, nucleated cells and purple rods. what can you conclude
Petty Reply
Study of micro organisation which we cannot see with naked eye...
shyam Reply
Despite their bad reputation, microbes are mostly beneficial or have a neutral effect on our lives. Microbiology is the scientific study of these microorganisms. Microorganisms are those organisms that are too small to see with the naked eye and include things like bacteria, fungi, and viruses.
not 'things'...'organisms' like bacterias, viruses and fungi
simi, it's not bacterias but bacteria which is the plural form of the word while bacterium is the singular of it
bacterium is obvio in a singular form but plural of bacterium is bacterias
Richard is right it's bacterium which is the singular form and plural is bacteria. *Bacterias* doesn't exist.
what is microbiology?
Sandeep Reply
what is microbiology
is the study of small microorganisms that can't be viewed by our naked eyes under a microscope
it's the study of microbes their classification, diversity, their cellular structure and processes, their applications and interaction with other organisms.
what is EMP pathway
which organism is implicated in meningoencephalitis
Peter Reply
Herpes virus
which mold is called dairy mold?
Geotrichum candidum
which infectious agent is the smallest
spore or virus
prion ....it is a single protein in a misfolded form..there is also a theory based on it
yup...m sry
yes it can be turned as a virus
which gram positive bacteria is responsible for food poisoning?
prion is not a living organism yet it is infectoois why
prions are virus like organism. and it is a misfolded protein that may cause disease to us.
Clostridium perfringens, B.cereus
Who is the father of the biology
I have one more question. . that who is the father of botany and medicine? ? can any one tell
define polar bond in simple way
Rashmi Reply
when there is formation of positive and negative poles i.e. one atom is +ve and other is -ve which further results in the dipole moment. Such bond is know as polar bond. It is a convalent bond only.
Hi everyone, is these site only about microbiology? I want a site which I can download articles on hematological and biochemical profile
Peter Reply
I think it is only about micro biology.
so whats happening
I am about to enter school and am going for MCB
Olugbenga Reply
What is DNA damage and repair
Sree Reply
removal of nucleotide bases from DNA is damage n addition or insertion of bases in DNA is repair.
replication is a term related to generation of new DNA from a parental DNA.
role of microorganism as pathogens
Parteek Reply
to live inside the host body, reproduction n destroy the immune system of host body.
what is replication
please give me ans
replication is a term related to generation of new DNA from parental DNA.
difference between endotoxin and exotoxin
Binkheir Reply
toxins released inside the cell or a body is endotoxin n toxins released outside the cell or a body is exotoxin.
Generally, exotoxins are produced by gram positive bacteria and endotoxins are the integral part of the cell wall of gram negative bacteria. But some gram negative bacteria can also produced exotoxins such as E.coli.
Yeah u r ryt aakarti exotoxins screted by gram postive bacteria nd secreted by cell surface and they are secondary metabolites ....On the other hand endotoxin released by gram negtive bacteria nd released inside the cell (lipopolysaccharide) ..
Heat stable lipopolysaccharides to be exact.
please I want the names of bacteria and the diseases they cause.
Ibrahim Reply
there are many we classify it according to their shapes gram negative or gram positive
so u may refer the book u guess or by when u want I can do a list for you and send u here
please do a list for me
I have the lost but it's too much to type ..
MSc entrance prepare books and questions LA etha base pani irukum..
Guhan Reply
kushal always prescott is the imp book to follow.search some objective mcqs books based on your syllabus
deepthi Reply
I want to clear entrance of ms university so I have no more idea so my preparation is based on my bachlor studies.
what are the opportunistic infection in aids stage
certain cancer or pneumonia 🤔

Get the best Microbiology course in your pocket!

Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Microbiology' conversation and receive update notifications?