Discussion on the types of culture media. Definitions and terminologies that should be noted in the discussion of the topic. Notes provided by the microbiology professor.

1. THE CULTURE MEDIA

2.  CULTURE - the growth or crop of
microorganisms obtained in a culture medium
after its incubation period.
 CULTURE MEDIUM - any material where
microorganisms may thrive for their nourishment
and reproduction.
 INCUBATION PERIOD – is the time needed to
let previously inoculated culture media to show a
distinct colony or colonies within a desired
temperature. It is also the time needed for the
microorganisms to adapt, grow and multiply in its
new environment.

3.  COLONY - a group of microorganisms growing
together characteristically in a culture medium.
 INOCULUM – the fished-out colony hanging on
the wire loop, cotton swabs, etc. that is ready for
transfer to another culture medium for cultivation
and/or for further isolation.

4. TYPES OF CULTURE:
 Contaminated culture – a culture that
accidentally contains one or more group of
microorganisms which should not be growing
there at all.
 Mixed- culture – means that there are two or
more desired species of microorganism living
in the culture medium.
 Pure culture – a culture that contains only
one group of microorganisms which is
usually obtained when microorganisms in a
culture medium are all of the same species.

5. TYPES OF CULTURE MEDIA –
according to PHYSICAL STATE
 Solid media/ Semi-solid media-
characterized by the sol-gel reversibility; those
media wherein agar is added as the solidifying
agent.
 Ex. Nutrient Agar, BAP, EMB
 Liquid Media – prepared without substances
like gelatin or agar.
 Ex. Nutrient broth

6. TYPES OF CULTURE MEDIA –
according to USE
 SIMPLE MEDIA – can facilitate different types of
microorganisms.
 ENRICHED MEDIA – are broth or semi-solid
medium containing a rich supply of special nutrients
that promote the growth of a particular fastidious
organism while not promoting the growth of other
microorganisms that might be present. Thus, the
desired species grows best and predominates in the
culture, and a pure culture could easily be obtained
from a mixed specimen.
 SELECTIVE MEDIA – have added inhibitors that
discourage the growth of certain organisms without
inhibiting the growth of the one sought.

7.  Differential Media- are used to grow several
species of bacteria, but each bacteria grown has a
distinctive appearance.
 Transport Media – have been devised to protect
pathogens present in clinical specimens that
might not otherwise survive or that might be
overgrown by non-pathogens during the transport
of the specimen from the patient to the
laboratory. Such a lapse of time may involve
either minutes, hours, or days.

8. 1. Nutrient Agar (NA) – consists of beef
extract, peptone, agar, and water. It is
often used as a base in the making of more
complex media.
2. Nutrient Broth (NB) –forms the basis of
most media employed in the study of
medical pathogenic bacteria.

9. Three types of nutrient broth:
 Meat infusion broths – consists of watery extract
of meat made by extracting lean meat for 24
hours at 2°C. Any remaining juice is squeezed
from the meat. The extract is then simmered for
15 minutes and filtered. Protein is removed in this
process and must, therefore be replaced by adding
1% peptone. Sodium Chloride is added last. These
broths generally contain a high percentage of
fermentable sugar, which makes them unsuitable
for many purposes,
 e.g., toxin production.

10. Three types of nutrient broth:
 Meat extract broths – are prepared from peptone
and commercial meat extracts. They can be easily
prepared and are widely used. However, they are
less nutritious than infusion and digest broths.
They are most suitable for preservation of stock
cultures.
 Ex: Brain- Heart Infusion (BHI) – most useful because it
allows many fastidious organisms to grow.

11. Three types of nutrient broth:
 Digest broths – consists of watery extract of lean
meat digested with a proteolytic enzyme. The
proteolytic enzyme employed varies, though
generally it is trypsin in the form of a pancreatic
extract.
 Ex: Hartley’s broth – ideal for growth of exacting
microorganisms.

12. 1. Blood Agar Plate (BAP) – used to encourage the
growth of bacteria which are unable to grow on
nutrient agar and to detect hemolytic streptococci.
2. Chocolate Agar Plate (CAP) – Used particularly as a
supply of factors essential for the growth of
Haemophilus sp., and when incubated with CO2 it is
ideal for the isolation and maintenance of Neisseria
meningitidis and N. gonorrhoeae.
3. Selenite F broth – an enriched medium for
salmonellae and some shigellae.
4. Milk agar- protein diet

13. 1. Mannitol Salt Agar (MSA) – encourages the growth
of Staphylococci but inhibits the growth of other
gram (+) bacteria. It is also a differential agar
because colonies or various species of Staphylococci
have different appearance on MSA.
2. Bordet-Gengou Medium – used in the isolation of
Bordetella pertussis.
3. Cetrimide Agar – used in the isolation of
Pseudomonas aeruginosa.
4. Thayer-Martin Agar – used in the isolation of genus
Neisserai.

14. 5. Lowenstein- Jensen Medium (LJ medium) –
used in the isolation of genus Mycobacteria.
6. Saboroud’s Dextrose Agar (SDA) – used in the
isolation of fungi.
7. Mueller- Hinton Agar (MHA) – for the primary
isolation of Neisseria gonorrhoeae and N.
meningitides It can also be used for the
determination of antimicrobial sensitivity and,
in particular, with the Kirby- Bauer technique.

15. 1. Eosin Methylene Blue (EMB) – frequently used
to separate and identify enteric gram (-)
organisms in fecal specimen. It can be used in
the isolation and identification of Candida
albicans.
 Lactose fermenters have blue- black center (LF organisms
produce acid that acts on the two dyes, Eosin and
Methylene blue).
 Non-lactose fermenters are colorless.

16. 2. MacConkey Agar (MAC) – both differential and
selective media, used for primary planting and
subculturing of enteric organisms.
 Lactose Fermenters appear pink to red (as a result of the
action of acid formed during the fermentation of lactose on
the indicator, neutral red).
 Non- lactose fermenters remain colorless.

17. 3. Salmonella – Shigella Agar (SSA)- a differential
and selective media designed specifically for the
isolation of pathogenic enteric bacilli belonging
to the Salmonella and Shigella genera.
 Lactose Fermenters yield red colonies.
 Non-lactose fermenters are colorless.
 H2S producers are colonies having black centers. (Ferric
citrate being the indicator).


18.  Stuart’s Transport Medium is ideal for swabs, eg.,
maintaining viability of gonococci on cervical
swabs.