Define Limitations for Standard or Total Plate Counts Method?
This method has certain limitations -
1. Microbial count depends on the type of media, incubation temperature, incubation time, distribution of the organism in the food sample and sampling method used.
2. Fastidious microorganisms may not be able to grow on the agar medium used.
3. Strict anaerobes may be overlooked because incubation conditions favour mesophilic aerobes.
4. Fungi may be underestimated because longer incubation time and lower temperature is required for fungal growth.
5. TPC indicates the size of the population but not the exact number of microbial cell because a colony may result from a clump of cells. Both pour plate and spread plate can be used for plating. Spread plate has advantage over pour plate as heat sensitive psychrophiles can be examined.
Also, colonial features can be used for presumptive identification. However, there may be a problem of spreaders and crowding of colonies especially when the agar is not completely dry which makes counting difficult. Further, microaerophiles grow slowly in spread plate.