<< 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 microbiology
vijay Reply
microbiology is the scientific study of microorganisms .microorganisms are those organisms that are too small to see with the naked eye ex-bacteria fungi
Yashkin
a branch of biological science concerned with organisms that can not be observed with a naked eye
Mooya
what are the types of granulocytes and explain
lord
polymorpho nuclear leukocyte, known as granulocyte are divide into three,1-polymorpho eosinophil 2-polymorpho basophil 3-polymorpho neutrophil
Musa
I want to know more about sample collection on the field
Ama Reply
blood collection and urinarysis
Lizzy
2143
Lizzy
yes
Lizzy
In the periodic table the number on the upper left hand side is what
Aurelia Reply
Hydrogen
Tob
am not talking about the elements
Aurelia
Is it the atomic number or the mass number
Aurelia
hologen
Usman
differences between acid fast and non acid fast bacilli
ANTHONY Reply
acid fast have cell wall that holds to carbol fuschin stain while non acid fast doesn't have. it readily releases out the primary stain the carbol fuschin.
LAFIA
where do I post a question that isn't related to that topic
eklectc
hi everyone
kennedy
hello
Olivia
for sure, this question is not related to the topic.
LAFIA
can someone explain the process of glycolysis and the electron transport chain? I'm so freakin lost. it loses carbons, gains hydroxyls, gains, loses Hydrogens....ugh it's like a foreign language to me! or direct me to a youTube video or something that will make this seem easier to concept?
eklectc
it's a loaded question, sorry!
eklectc
why is DNA a genetic material
Mcbeth Reply
DNA is genetic material because it contains chromosome contains the traits which includes characters and behavioral characteristics
chima
why is it difficulty to classfy protista
Tanaka
Good
Eddy
what is infection prevention
Muhammed Reply
good hygiene
Dhaqan
way of preventing disease causing germs
henry
maintenance of sterilization
Pooja
h
Faustina
describe the components of the epidemiology triangle
Muhammed Reply
Hai
Nantongo
hii
Md
where from you
Md
i am Indian
Md
you
Md
Hello friend
effiong
How are you people doing
effiong
أ‌) Host factor ب) pathogen ج) environment
Widad
Hello
Kofi
Hi
Widad
hey hi
kalai
The epidemiologic triangle is made up of three parts: agent, host and environment
Princess
please can a microbiologist will work at hospital
Usman
what are the fluids used in biochemistry Lab used to diagnose diseases
Jb Reply
fadumo qule a gemil3
fadumo Reply
Faadum mahamud disease micro biology
fadumo
makuway diinkaraan suaalo
fadumo
history of microbiology
Balqees Reply
Penicillin is caused by what microorganism
Balqees
Penicillin is caused by what microorganism
Balqees
penicillium notatum
Pooja
M sorry I mean penicillin is caused by what Fungi
Balqees
penicillium fungi
Pooja
when I finish with my bsc in microbiology where wil I work
Usman
Why can we see ourselves in a mirror?
Usman
mention 5 characteristics of prokaryotic cell and also 5 characteristics of euryotic cell
Grace Reply
PROKARYOTES _ does not have nucleus _does not have membrane bound organels like eukaryotes -does not have endoplasmic reticulum _does not have a mitchochondrion _it have plasmid instead of chromosome EUKARYOTE S _have true nucleus _have all membrane bound organels _have mitochondria have
Pooja
continuation _have endoplasmic reticulum _have chromosomes does not have plasmid
Pooja
antigenisity define
kalai
explanation of spores
nahida Reply
what specific types of biological macromolecules do living things require?
Jonathan Reply
define spores its classification
nahida
define spores its structure and classification
nahida
what is a complement
Alecia Reply
something which completes or combine with something else to make it complete.
Kosi
hello
Kosi
medical microbiology
Kosi
you?
Kosi
hi
Amina
Guys who's doing nursing in here
Mumba
I have a question
Mumba
what's the importance of microbiology in nursing
Mumba
yah
Mumba
wow..nice meeting you
Kosi
thanks
Mumba
for
Mumba
anytime
Mumba
microbiology also important for understanding the communicable or non-communicable disease in our hospitals...which is very important for patients and healthy people.
Kiran
what is a microbial flora
Chetan
normal microbial flora
Chetan
Definition of microbiology?
Mohamed Reply
study of microorganisms is known as microbiology
Pooja
no
Mumba
microbiology is the study of small or minute organisms that cannot be seen with our naked eyes but with the aid of a microscope
Mumba

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?

Ask