Test for aerobic mesophilic and thermophilic spore count

Hello

I am searching for a procedure for testing for aerobic mesophilic spore count and aerobic thermophilic spore count (liquid food product). I have access to standard lab equipment including a water bath and incubators.

Is it possible to do this test on Petrifilm? Or will this have to be a pour plate technique?

In order to enumerate just the spores, you need to kill off the vegetative cells first.
The way we do this is to prepare the dilution series as normal, then immerse these tubes into a waterbath set at 85C.
Let the tubes get to and stay above 80C for at least 10 minutes then cool.
Plate out as normal on Plate Count agar or petrifilms and incubate as indicated below:

Aerobic Mesophilic 30C x 48±2h
Aerobic Thermophilic 55C x 48±2h

This is an in-house method based originally on an ICMSF method from waaaaay back when I started in microbiology but it seems to work fine. One of my leas favourite methods, getting the tubes to 80C can take a while!

Thank you Dr.Des

This is pretty much the method we'd come up with so it's good to get some confirmation!

rwalker