In the production of pharmacological products of various types such as antibiotics, federal regulations in the United States and similar regulations in other nations require sterility testing to ensure that the products are substantially free of microorganisms such as bacteria, fungi and molds. In the past two methods have been used to carry out such sterility testing.
In one method referred to as the direct method, the product material to be tested is inoculated into a medium that has been prepared and tested to ensure optimum conditions for the growth of the specific contaminant organisms being tested for. Such systems are somewhat limited in that they require a specific volumetric to area ratio, in order to control the oxygenization of the media and these volumetric ratios are sometimes difficult to achieve in practice.
The second method involves the use of a membrane filter as a screen employed to strain and concentrate the contaminant microorganisms from the test product. Thereafter the membrane filter is divided into a number of portions equal to the number of culture media used and each portion is immersed into one culture medium for incubation at a specified temperature for a predetermined period. When the incubation period has been completed the presence of an unduly high level of the contaminant organism in the test product is determined by observation of color changes or turbidity in the incubated culture medium. Typically, for bacteria, a thioglycollate medium has been utilized, which includes a resayurin additive to provide for color indication, and also agar to inhibit diffusion throughout the medium. Immediately after immersion of the filter, this medium is exposed to air until the upper 1/3 of the solution turns pink, indicating oxidization of that portion of the culture medium. Since the agar gel prevents diffusion of the oxidized fluid throughout the culture medium, the result is that the upper portion of the medium provides an environment which promotes the growth of aerobic bacteria, while the lower part of the medium fosters the growth of anaerobic bacteria.
A fluid which has particularly been useful for determination of the presence of fungi is soybean-casein digest medium. Another material which is utilized for this latter purpose is sabourin. By inclusion of surfactants in the media, pharmacological products which include oils or petroleum may be tested. If the pharmacological product is a powder, it may be dissolved in a suitable sterile solution and the resulting liquid is then treated in the same manner as would be a liquid product.
It has been found that in large scale production processes these testing methods are awkward and expensive. For example, the requirement of maintaining sterility while dividing the filter material into two separate portions before introducing it into the media for testing is difficult, as is also the requirement that great care must be taken at each step of the process not to introduce any contaminant microorganism overexposure to the media.