To perform the pour plate inoculation method, a serial dilution should be prepared first, followed by dispensing the sample into a dish, adding melted agar, and mixing. After solidification, the plate is incubated and observations are made about colony growth, number, and characteristics.
Firstly, perform a serial dilution of the bacterial culture to ensure a countable number of colonies are obtained. Once dilutions are prepared, the pour plate method follows these steps:
Label the empty sterile petri dishes with the date, type of media, and serial dilution factor.
Using a pipette, dispense a measured volume of the diluted sample into the center of the labeled petri dish.
Sterilize an inoculation loop in a flame until it is red hot, then allow it to cool.
Gently pour the melted agar media into the petri dish, swirling it to mix with the inoculum.
Allow the agar to solidify at room temperature without disturbing it.
Incubate the plates at 35°C ±2°C for 18–24 hours as directed by your instructor.
After incubation, observe the petri dishes for bacterial growth:
Note the number and appearance of colonies within the agar and on its surface.
Colonies that have grown within the agar will typically appear smaller and may have a different texture compared to those on the surface.
Examine the agar surface for colony growth, which indicates bacterial reproduction. Record the number of colonies, configuration, margin, elevation, texture, and pigmentation. If no growth is observed, consider potential reasons such as improper sterile technique, a non-viable sample, or incorrect incubation conditions.