Growth Promotion Test in Microbiology

What is a Growth Promotion Test?

Growth promotion testing of culture media is an important part of microbiological testing in support of pharmaceutical quality. The growth promotion test is a quality control requirement that confirms the ability of a new batch of media to support growth of a predetermined selection of representative microorganisms.

Why GPT is done?

The purpose of the test is to ensure the quality and functionality of the media before using it for analysis. GPT should be performed on solid media and broths but not for dilution solutions and rinsing fluids. GPT is performed by inoculating the product with = 100 CFU of microorganisms, as defined by the pharmacopoeia.

What Does USP Say About GPT?

USP growth promotion testing requirements for solid and liquid microbiological growth media is described in <61> as:

"For solid media, growth obtained must not differ by a factor greater than 2 from the calculated value for a standardized inoculum. For a freshly prepared inoculum, growth of the microorganisms comparable to that previously obtained with a previously tested and approved batch of medium occurs. Liquid media are suitable if clearly visible growth of the microorganisms comparable to that previously obtained with a previously tested and approved batch of medium occurs".

USP also stipulates using less than 100 cfu during this process.