Why Petridishes are inverted during incubation period

1.0 OBJECTIVE

To lay down a procedure explanation of why Petri dishes are inverted.

2.0 SCOPE

This SOP is applicable for explanation of why Petri dishes are inverted in microbiology Lab.

3.0 BACKGROUND

NIL                                       

4.0 RESPONSIBILITY

4.1 QC-microbiologist  

4.2 QC-Executive         

4.3 QC-Head

5.0 PROCEDURE

5.1 A Petri dish (plate) with “solid” culture media is kept in an inverted position (upside down) during incubation so that condensation droplets will not fall on the agar's surface (as such droplets are potential sources of contamination).

5.2 Asides that, the evaporation of water from the media if incubated in the normal position could cause the media to start drying thereby affecting the ideal microbial growth conditions and increasing microbial count errors.

5.3 Placing plates upside down also makes them easier to handle and identify since the labels are placed underneath the dishes and not on the lids.

5.4 It should however be noted that pouring media at higher temperature causes excessive moisture accumulation on the lids of the Petri dishes. So, it's advisable that you start pouring when the temperature is about 45°C (cool-down period).