Download Microbial metabolism part II

Differential and Selective Media
Prepared BY
Ms.c: Abed Al Rahman I. Hama
Type of media
Purpose
Define : The media used in the laboratory have to be chosen to
suit the nutritional requirements of the species of organism to
be grown. Isolation from a mixture can sometimes be facilitated
by the use of media designed for a special purpose.
Types of media:
a) Transport media: its media for preserve the microbe in same number and
condition as in patient (no nutrient, inhibition of lethal effect of destructive
enzymes, and preserve the microbe from effect of oxidation).
b) Isolated media:
1) Simple media (basic media):
Peptone (peptone + NaCl)
Nutrient broth (extract meet + peptone + NaCL)
Nutrient agar (nutrient broth + solidyfing agent)
2) Enrichment media
Blood agar: nutrient agar +5% blood (red color)
Chocolate agar : heated blood agar (brawn color) specific media for
Hemophilus influenzae and Neisseria gonorrhoeae
Differential vs Selective Media
• Selective media: Media – is a type of media that
contains certain chemicals that will permit only certain
groups of genus of bacteria to grow on it. Lowenstein
Jensen media for T.B. which contain malachite green
as inhibitor.
• Differential: Media – is a media type that will
distinguish biochemically between related groups of
organisms. Some organisms will incorporate some of
the chemicals in their make up creating specific
colored colonies.
• Ex: MSA, Mac Conkey,EMB
TSA
• Trypticase Soya agar
Nutritious medium for a
growth of a huge variety
of bacteria.
• No differential
• No selective
http://www.austincc.edu/microbugz/assets/images/MSA.jpg
Mannitol Salt Agar
• MSA: Mannitol Salt Agar
• Selective medium for Gram positives. Inhibit
Gram negatives.
• Differential: mannitol fermenters
• Medium specific for staphylococcus  contains
7.5% salt which is inhibitory for most other
bacteria.
• Contains the sugar mannitol and the pH
indicator phenol red  fermentation of mannitol
 acid produced  media turn yellow
MSA
• Positive: Growth,
yellow
• Negative: No growth,
no change of color
http://www.austincc.edu/microbugz/assets/images/MSA.jpg
Eosin Methylene Blue
• EMB: Eosin Methylene Blue
• Selective medium for Gram negatives.
Inhibit Gram positives.
• Differential medium for lactose fermenters
– Lactose fermenter will produce dark red
colonies
• E. coli produce a characteristic green
sheen
EMB
• 1: E. coli  green
• 2: no lactose
fermentation
• 3: lactose
fermentation
• 4: no growth
http://www.microchemlab.net/bact5.jpg
http://iws2.ccccd.edu/dcain/CCCCD%20Micro/EMBplate.jpg
McConkey agar
• Selective medium for
Gram negatives
• Differential medium for
lactose fermenter
bacteria
• Positive for lactose
fermentation =Colonies
bright pink
• Negative for lactose
fermentation= colorless
colonies
http://www.emlab.com/m/media/Ecoli_Feb07.jpg
• Mueller-Hinton agar plate (MHA)
• Use : For antimicrobial susceptibility testing of a
variety of nonfastidious, rapidly-growing
microorganisms.
• Control organisms :
Escherichia coli ATCC25922 , Staphylococcus
aureus ATCC 25923, and Pseudomonas
aeruginosa ATCC 27853 : Growth ,Inhibition
Zone followed Standard interpretative
• Salmonella-Shigella agar plate (SS)
• Use : For the selective isolation and differentiation of
pathogenic enteric bacilli, especially those belonging to
the genus Salmonella. This media is not recommended
for the primary isolation of Shigella species. Lactosefermenting bacteria such as Escherichia coli or
Klebsiella pneumoniae appear as small pink or red
colonies. Lactose-nonfermenting bacteria such as
Salmonella species, Proteus species and Shigella species
appear as colorless colonies. Production of H2S by
Salmonella species turns the center the colonies black.
• Control organisms :
Salmonella typhi : Colorless colonies, black
centers.
Escherichia coli : Pink colonies
• Sabouraud Dextrose Agar plate (SDA)
• Use : For the cultivation of pathogenic and
nonpathogenic fungi, especially dermatophytes. The
medium may be made more selective for fungi by
the addition of specific antibiotics such as
chloramphenicol. For the cultivation of yeast and
filamentous fungi.