Question

Q1 ) Nutrient broth is referred to as a general purpose medium. Explain what is meant by this statement.  

When considering your answer, you may wish to consider what substance nutrient broth is prepared from in addition to the further information about microbiological growth media on pg. 45 of the practical manual.

page 45 => Bacterial growth media – nutrient broth

The medium used in this practical session to study the growth of bacteria is a liquid medium termed nutrient broth (NB). It is a general-purpose meat-based medium used for routine culture of many bacteria that do not have special growth requirements.

Nutrient medium of various kinds is available commercially (from companies such as Oxoid and Difco) as a desiccated product (i.e. a powder). To prepare nutrient broth, water is added to an appropriate quantity of the powder and the dissolved product is dispensed in the required quantities (e.g. as 10 ml broths). It is then sterilised by autoclaving (steam under pressure for an appropriate time) to kill all contaminating life-forms. Once sterile, it can be stored at room temperature until required.

Answer 1

Nutrient broth is present in the liquid form and it is given to bacteria for expanding in the numbers or maintaining the microorganisms stocks . In general, they are used to grow fastidious organisms( Neisseria gonorrhoeae, which requires blood or haemoglobin and several amino acids and vitamins to grow). For storage they are kept in the culture bottles .they lacks the agar (solidifying agent) component so they are liquid. Nutrient broth comprised of the peptone (provide nitrogenous compounds, vitamin B complex, amino acids and other essential growth nutrients),beef extract(It contains water-soluble substances of animal tissue, which include carbohydrates, organic nitrogen compounds, water soluble vitamins, and salts.) and sodium chloride (used to maintain the osmotic balance). Beside this serums and blood may also be added as per the requirement .so they are called the general media due to their non-specific needs and growing purpose only.

while the nutrient agar is present in the semisolid form which upon further use classified as the slants (used for the pure culture colony isolation) and slants for semi –long term storage and transport . It supports the growth of wide range of non-fastidious organisms (Enterobacter aerogenes - non-fastidious). Nutrient agar contains nutrients that suitable to subculture a wide range of microorganisms and makes it an excellent agar media to check on the purity before any biochemical or serological test. Nutrient agar is composed of peptone, beef extract, yeast extract, agar and sodium chloride.