Ann: Successful UK Lab tests, page-260

Direct Inoculation Method:

A. Sterility Test MethodsThe USP describes two general methods for conducting the test: the direct transfer, or direct inoculation, method and the membrane filtration method.
As the name indicates, the direct inoculation method involves the aseptic transfer of a sample of test product solution into the sterility test growth medium. To use this method, it must first be demonstrated that the product solution itself does not inhibit the growth of typical “indicator” microorganisms specified in the USP method. It should be self-evident why it is important to perform testing to negate the chance of product inhibition of possible microbial contaminants, as this is the purpose of the sterility test.

The direct inoculation method, while not theoretically complex, requires the utmost technical precision and aseptic manipulation techniques for proper execution. As a consequence of the repetitive motions involved, it is prone to human error.

Hope this helps...