Let’s look at that as two different parts of the process. You would certainly want to have an operational qualification of the equipment. Then as part of the performance aspect, you would be looking at the sterilization of the media, and any associated hold times. So the whole aspect of the sterilization (lack of contamination, I guess, is a better phrase) for the media is another consideration.
There’s a family of issues here that are related, but they probably need to be distinguished. Sometimes the easiest way to resolve a complex problem is to attack it in parts. The first is, can you sterilize the fermenter? The second is, can you sterilize the medium in the fermenter? And, thirdly, can you operate the fermenter after the medium has been sterilized to grow the organism you want to grow? The first part, you can address by typical thermocouple monitoring methods, and even biological indicators, if necessary. The second part you can address by putting the medium in, running the sterilization cycle, doing some temperature monitoring, perhaps also doing some sampling. But, if you’re going to sample and test, it’s important to be careful how you sample, because if you don’t sample in an aseptic manner, it may not be a valid test. One also has the issue of whether or not you can find anything in the test article; in other words, can the test medium actually grow organisms that might have been “in the environment” and, therefore, inadvertently not sterilized by the sterilization operation So the fact that you get a negative test result doesn’t necessarily mean anything and there needs to be some background laboratory work to show that you could have, in fact, found expected contaminants if they were present. Then, finally there is the question of aseptic operation of the fermenter, which one can address by running some batches and seeing if you get results that are in line with your expectations and your control limits. It’s best to approach it in parts rather than trying to do it in a single approach and a single experiment.
In the case of a classical fermentation, there is a fourth issue and that is a foreign organism that may enter or survive the original sterilization of the fermenter and the media, itself. It may or may not be an issue. It could be purely an economic issue if a foreign organism were to be there. That’s probably not true in the biotech area, but it can very certainly be true in the classical fermentation area where a foreign organism could have an effect on the productivity of the organism of the drug you are producing. For example you may get 3 grams per liter throughput instead of 4 grams. So, your productivity may go down but it really may have no adverse effect on the material in your fermenter. There are other issues, and based on industry experience, foreign organisms, especially on long-term fermentations are not uncommon. When you talk about hundreds of hours of fermentation, having foreign organisms all of a sudden show up is not unusual, and many firms will have experienced the situation of having them show up in the late logs. Just to answer the question about Log 0, Log 0 is the start of the fermentation. Those are the kinds of things you have to examine. In some cases, it may be a big issue; in other cases, it may not be.
Another detail to watch out for is, if you’re running recombinant bacterial fermentations, where you might use antibiotics to maintain selective pressure. That may be how you have to run the fermentation to make your product, but, as you might imagine, if you have tetracycline in the medium, you’re not going to find too many organisms when you go to sample it. There, it’s best to remove those kinds of agents from the test, just so that you can have a reasonably valid result. In conclusion, validating a fermenter and a fermentation process is quite different from validating an autoclave and a terminal sterilization cycle for a finished drug product, or from validating equipment or materials that would be used in an aseptic filling operation for a drug product. Obviously, terminal sterilization of a drug product is your last opportunity to kill any microorganisms in the product before it gets to the consumer. In the fermentation process even if you had some contamination it may or may not be significant. If you have some contamination and it can be “cleaned up” in further processing steps, fine; if it cannot be “cleaned up”, what happens is that batch is dumped down the drain, so it never reaches consumer. So these are very different things, you are trying to accomplish one thing when you’re dealing with terminal sterilization of drug products; and you’re trying to accomplish something else, or something slightly different when dealing with a fermentation process.
