Download LAB:4 CULTURE MEDIA

LAB:3
CULTURE MEDIA
CULTURE MEDIA
- Culture media are used for the recognition
and identification of microorganism. The
media are contained either in test tubes,
plates (Petri dishes) flasks or screw
capped bottles which must be thoroughly
cleaned before use, then the medium and
the container are subsequently sterilized
by heat.
Blood agar and
nutrient agar
(Solid culture medium)
nutrient broth
(Fluid culture medium)
Common ingredients of culture
media
1. Peptone
2.Meat extract
3.Nacl
4. Agar agar
a. Melting point 92-95 c
b. solidifing point 42-45 c
c. concentration 1.5-2%
Most pathogenic bacteria have restricted pH (7.2 – 7.4 )
. Therefore, pH of the media should be adjusted using
TYPES OF CULTURE MEDIA :
- Culture media can be classified according
to:
A - Physical state ( consistency ) of
the media
1.Liquid (Fluid) media e.g. nutrient broth,
peptone water, brain heart infusion . They
are commonly
used
for
primary
cultivation.
2.Solid media e.g. nutrient agar ,blood agar,
MacConkey's agar which are commonly
used for cultivation of bacteria.
3. Semisolid media used for cultivation of
spirochetes and to study motility. They
contain 0.4 – 0.8 % of agar agar.
Blood agar and
nutrient agar
(Solid culture medium)
nutrient broth
(Fluid culture medium)
1)Simple or basal media e.g. nutrient agar and
nutrient broth.
They are used for the cultivation of common
microorganism but not for the fastidious bacteria.
Nutrient agar
Nutrient broth
Simple culture media
2)special-purpose media e.g. enriched, selective,
differential, transport, sensitivity test, etc…
-Simple media enriched with appropriate
substance ,e.g. Blood ,glucose ,serum and
ascetic fluid ,most commonly used to cultivate
fastidious microorganism like streptococci.
Chocolate agar
Blood agar
(Enriched media)
-Containing inhibitory substance ( e.g. bile salt ,antibiotic,
dyes…etc) which favour the growth of concerned
microorganism and inhibit the growth of other . e.g.
Maconkey's agar, Potassium tellurite agar, Bismuth sulphite
agar , Deoxycholate citrate agar…etc
Slective medium for gram negative bacilli (contains bile salts which
inhibit the growth of gram positive microorganisms)
-Certain species produce characteristic growth
that can be easily recognized, or can produce
certain effects in the media e.g. hemolytic and
non-hemolytic
species
on
blood
agar
,MacConkeys agar differintiates between lactose
fermenter and non lactose fermenter gram
negative bacilli.
MacConkey′s agar (selective and differential medium)
selective for gram negative bacilli and differentiate between
lactose fermenter and non lactose fermenter gram negative
bacilli)
Antibiotic susceptibility testing on Mueller-Hinton
agar
- This test is used to know the appropriate antimicrobial
agents to be used for the treatment of the causative
bacteria.
Disk diffusion test
-The culture media is inoculated by the pathogenic
bacteria and a paper discs impregnated by different type
of antibiotic (Each disc for specific antimicrobial agent
eg disc for ampicillin and other for gentamicin, amikacin
rifampicin …etc) are placed on this culture media.
-The culture is incubated at 37 C for 24-48 hr according
to the type of mo. The test results are read as the
following:
1- A Zone of inhibition of growth (no growth around the
disc) the bacteria is sensitive to this agent.
2- If the growth of mo reached the edge of the disc this
mo is resistant to this antimicrobial drug.
No zone of no
no inhibition
Growth to
the edge of
the disc
resistant
Zone of
inhibition
No
growth of
m.o
sensitive