Transcript Selective media are used for the growth of only select

Selective media
Selective media are used for the growth of
only select microorganisms.
For example, if a microorganism is resistant
to a certain antibiotic, such as ampcillin or
tetracycline , then that antibiotic can be
added to the medium in order to prevent
other cells, which do not possess the
resistance, from growing.
•Media contains some dyes such as crystal
violet , methylene blue and eosin Y. Other
media contains bile salts which inhibits the
growth of Gram positive bacteria
Thiosulfate citrate bile salt Agar (TCBS)
Selective media for Vibrio Cholerae
because the high pH which inhibit Gram
+ve bacteria &most of Enter bacteria
Aspergillus Niger sabouraud dextrose agar
Selective media for fungi because the pH5.6
Differential media
• Differential media or indicator media
distinguish one microorganism type
from another growing on the same
media.
•This type of media uses the biochemical
characteristics of a microorganism growing
in the presence of specific nutrients or
indicators (such asneutral red ,phenol red,
methylene blue or eosin Y) added to the
medium to visibly indicate the defining
characteristics of a microorganism.
Blood agar plates are often used to
diagnose infection. On the right is a
positive Streptococcus culture; on the
left a positive Staphylococcus culture
Examples for selective and
differential media
• Eosin methylene blue agar (EMB)
• Mannitol Salt Agar (MSA)
• MacConkey Agar (Mac)
• Salmonella Shigella Agar(SSAgar
Eosin methylene blue agar (EMB)
• Eosin methylene blue agar (EMB) is a
selective and differential medium used
to isolate fecal coliforms.
• Selective because the contains of
Eosin Y and methylene blue are inhibit
growth of most gram positive bacteria
Differential because the contains of :
1-pH indicator are E & MB dyes which combine to
form a dark purple precipitate at low pH
2-lactose carbohydrate sources which encourage
the growth of fecal coli forms and provide a
means of differentiating them as:
•
Lactose fermenter produced acid and gives
pink colors.
•
Non-lactose fermenter normally-colored or
colorless colonies
Eosin methylene blue agar (EMB)
• E. coli results in a metallic green sheen
on EMB .
Enterobacter aerogenes and Enterobacter
cloacae both form pink
colonies on EMB.
Salmonella typhimurium and Pseudomonas
aeruginosa both form colorless colonies on
EMB.
MacConkey Agar
• MacConkey Agar (MAC) is a selective
and differential medium designed to
isolate and differentiate enterics based
on their ability to ferment lactose.
• Selective because the contains of Bile
salts and crystal violet inhibit the
growth of Gram positive organisms.
MacConkey Agar
Differential because the contains of :
•Lactose as a source of fermentable
carbohydrate, allowing for differentiation.
Lactose fermenter will gives red colors
lactose non- fermenter will give
normally- colored or colorless colonies.
•Neutral red is a pH indicator that turns
red at a pH below 6.8 and is colorless at
any pH greater than 6.8.
•Nonfermenters
will
produce
normallycolored or
colorless
colonies.
Lactose
fermenters
will
produce
pink colors
colonies
•
Klebsiella pneumoniae
Micrococcus gluteus does not grow
on Mac agar
Escherichia coli on Mac
E.Coli & Serratia marcesens on Mac
agar
Mannitol Salt Agar (MSA)
• Mannitol Salt Agar (MSA) is a selective and
differential medium.
• Selective because contain the high
concentration of salt (7.5%) which selects
for members of the genus Staphylococcus,
since they can tolerate high saline levels.
• Organisms from other genera may grow,
but they typically grow very weakly.
MSA differential because the
contains of :
1. pH indicator phenol red which gives
yellow color at low pH.
2. Mannitol sugar as a carbon sources
which encourage the growth
Staphylococcus aureus and provide a
means of differentiating them from the
other Staphylococci which will not
ferment mannitol.
Staphylococcus epidermidis
Staphylococcus aureus yellow color
The Staphylococcus aureus will give
yellow. The Serratia marcesens does not
grow on MSA
Streptococcus agalactiae does not
grow on MSA. Staphylococcus
epidermidis grows but does not
ferment mannitol
Salmonella Shigella Agar (S.S Agar)
Salmonella Shigella Agar is a selective and
differential medium.
•Selective for Salmonella & Shigella because its
contain Na-citrate & bile salts which inhibit Gram
+Ve & most of Gram - Ve bacteria .
•Differential between Salmonella & Shigella
because Salmonella can utilize the citrate a
carbon source & give a black color as a result
H2S produces .
But Shigella can not utilize the citrate a carbon
source & give colorless
Salmonella on SS agar give a black
color as a result H2S produces
Never Ever Trust The
Selectivity Of The
Selective Media
References:http://en.wikipedia.org/wiki/Mannitol_Salt_Agar“
http://gateway.nlm.nih.gov/MeetingAbstracts/102265145.html
2003http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Medi
a.html
2003http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Medi
a.html#Bristol's_Medium
http://books.google.com/books?id=AtjDUn5KfG0C&pg=PA172&ots=
H0ClQyGxd4&dq=selective+and+differential+media&sig=6f8CshJIE
PuoTNVVerDwYNttk_o#PPP15,M1
http://www.arabslab.com/vb/showthread.php?t=2415
http://en.wikipedia.org/wiki/Image:Proteus_McConkey.jpg#file
http://www.biomedcentral.com/content/figures/1471-2180-4-6-4.jpg
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