What is the difference between pour plate method and spread plate method in isolation of bacterial colonies

Pour-plate method and Spread-plate method are used for quantification or enumeration of bacterial sample.

The difference between pour-plate method and spread-plate method are as follows:-

[A] Procedure: -

For pour plate-

• Inoculum from a sample is placed in the center of sterile Petri dish using a sterile pipette. Molten cooled agar (approx. 15mL) is then poured into the Petri dish containing the inoculum.

For spread plate-

• Inoculum from a sample is pipette out and spread evenly on sterile nutrient Agar by spreader.

[B] Amount of Inoculum:-

For pour plate-

• Inoculum is more i.e 1ml

For spread plate-

• Inoculum is less i.e. 0.1ml

[C] Growth of colonies:-

For pour plate-

• Colonies grow in and on solidified medium.

For spread plate-

• Colonies grow only on surface of medium.

[D] Mixing of inoculum and medium:-

For pour plate-

• After pouring molten agar on inoculum the plate is gently swirl.

For spread plate-

• Inoculum is spread on surface of medium (agar) by sterile glass rod spreader.

[E] Surface area covered by sample:-

In pour plate-

• More surface area is covered as the sample is spread throughout the media.

In spread plate-

• Sample is spread only to a limited area i.e. only on the surface of agar.

[F] Uses:-

For pour plate-

• It is used to determine CFU/ml or PFU/ml.

For spread plate-

• It is used to isolate specific clonal colonies.

[G] Advantage:-

Pour plate-

1. It allows the growth of microaerophiles.
2. It helps in identification of bacteria, i.e. whether the bacteria is an aerobe, anaerobe or facultative aerobe.

Spread plate-

1. Picking surface colony will not interrupt other colonies by digging out of agar.
2. Get even distribution of colonies.

[H ] Disadvantage:-

For pour plate-

1. Picking subsurface colonies can interrupt other colonies by digging out of agar.
2. Don't get even distribution of colonies.

For spread plate-

1. It doesn't allow growth of microaerophiles.
2. It doesn't allow growth of obligate anaerobes.

[I] Benefits:-

For pour plate-

• It is beneficial to isolate certain bacteria which are motile and don't grow as colony.

For spread plate-

• It is beneficial for isolation of bacteria from soil or water