Fundamentals of Microbiology (2+2)

Procedure

 Plating

Pour plate technique

·         Melt sterile plate count agar medium by boiling. Cool the molten agar and maintain in a water bath at 45°C - 47°C.

·         Label the petridishes at the bottom indicating the dilution, sample details etc. using a glass marker

·         From the dilutions transfer 1 ml of inoculum into petri dishes (two dishes for each chosen dilution)

·       Pour approximately 20 ml of molten, tempered agar into each of the petri dishes and mix with the inoculum by swirling    the plates a few times.

·         Allow the plates for sometime to solidify the agar and incubate at appropriate temperature in inverted position.

·         After incubating for 24 h or 48 h observe for colonies in each dilution and record the results.

·         Look for the gradual reduction in the crowding of colonies with increased dilution.

·         At some higher dilution, the colonies would be well distributed so that each colony could be isolated. Each colony has grown from a single bacterium, thus this method helps in purifying mixed cultures of bacteria.