Classification of Bacterial Culture Media On The Basis of Purpose
Classification of Bacterial Culture Media On The Basis of Purpose
Classification of Bacterial Culture Media On The Basis of Purpose
1. General purpose media/ Basic media. Basal media are basically simple media that supports most non-
fastidious bacteria. Peptone water, nutrient broth and nutrient agar (NA) are considered as basal
medium. These media are generally used for the primary isolation of microorganisms.
Nutrient Agar
Addition of extra nutrients in the form of blood, serum, egg yolk etc, to basal medium makes
enriched media. Enriched media are used to grow nutritionally exacting (fastidious) bacteria. Blood agar,
chocolate agar, Loeffler’s serum slope etc are few of the enriched media. Blood agar is prepared by
adding 5-10% (by volume) blood to a blood agar base. Chocolate agar is also known as heated blood
agar or lysed blood agar.
a. Selective medium
Principle: Differential growth suppression
Selective medium is designed to suppress the growth of some microorganisms while allowing the
growth of others. Selective medium are agar based (solid) medium so that individual colonies may be
isolated.
4. Differential/ indicator medium: differential appearance: Certain media are designed in such a way that
different bacteria can be recognized on the basis of their colony colour. Various approaches include
incorporation of dyes, metabolic substrates etc, so that those bacteria that utilize them appear as
differently coloured colonies. Such media are called differential media or indicator media. Differential
media allow the growth of more than one microorganism of interest but with morphologically
distinguishable colonies.
5. Transport media: Clinical specimens must be transported to the laboratory immediately after
collection to prevent overgrowth of contaminating organisms or commensals. This can be achieved by
using transport media. Such media prevent drying (desiccation) of specimen, maintain the pathogen to
commensal ratio and inhibit overgrowth of unwanted bacteria. Some of these media (Stuart’s & Amie’s)
are semi-solid in consistency. Addition of charcoal serves to neutralize inhibitory factors.
Cary Blair transport medium and Venkatraman Ramakrishnan (VR) medium are used to
transport feces from suspected cholera patients.
Sach’s buffered glycerol saline is used to transport feces from patients suspected to be suffering
from bacillary dysentery.
Pike’s medium is used to transport streptococci from throat specimens.
6. Anaerobic media: Anaerobic bacteria need special media for growth because they need low oxygen
content, reduced oxidation –reduction potential and extra nutrients.
7. Assay media. These media are used for the assay of vitamins, amino acids and antibiotics. E.g.
antibiotic assay media are used for determining antibiotic potency by the microbiological assay
technique.