Question

why is it important to study single colonies of bacteria?

what is a colony and how does it relate to a bacterial cell?

what are the advantages of growing bacteria on a plate vs broth?

how can you tell whether the colonies on your plate are from the original culture and not contamiinants?

Answer 1

Answer:

1. It is important to study single colonies of bacteria because presumably the single colony has risen from one bacterium and hence it is like a pure culture of a single bacterium and thus it shows all traits of that bacterium without any changes. As mutations are very common in unicellular organisms, it helps to avoid mutants and hence modified characteristics by using a single colony and use its traits to identify the organism positively.

2. As mentioned above a colony of bacteria is practically risen from a single cell. When bacterial cells divide by binary fission, their separation is at times incomplete leading to arrangements of chains, bunches and tetrads depending on planes of division. Also, when separated, they remain close vicinity and thus my multiple divisions they accumulate into a visible to naked eye growth known as a colony.

3. The bacterial growth happens best in a liquid broth medium but yet the growth of bacteria on solid agars is sought after because of advantages of:

• ease of use,
• visible contamination if that occurs, in broth it may be difficult to identify contamination
• possibility of picking a single colony and hence avoid mutants and contaminants if any.

4. On a solid agar plate the method used for bacterial isolation in laboratories is streaking. This creates a visible line of tracts from initial inoculum until end of tail with isolated colonies. Any colonial growth not on these streaks will be a contaminant from media or introduced from environment while petri plate was open and in use. Also, when working with pure cultures all colonies show similar characteristics, e.g. raised or flat, regular or irregular edges, colour if pigmented etc. More than one type of colony will also indicate contamination. Talking about streaking again, if a growth appears on a later streak which was missing from the previous streaks, it indicates contamination introduced by the microbiologist / technologist whilst working by use of unsterile loop or improper aseptic technique.