Understanding closed ecological systems
Richard Prince, Ph.D.
A recent article in ASM News, published by the American Society of Microbiology, caught my eye. It discussed progress made in the area of closed systems stemming, in part, from America`s space program. The article focused on the increasing understanding of the ecology of microorganisms in closed systems. It got me thinking about the ecology of microorganisms in (closed) industrial processes and systems (this column is intended as a thought piece only).
Technically, closed ecological systems do not exist in, say, pharmaceutical manufacturing processes, because equipment is periodically disassembled or cleaned as part of a preventive maintenance program. But, for the purposes of discussion, let`s consider your firm`s water system, some manufacturing processes or even testing isolators to be forms of closed ecological systems. Would they be expected to also produce stable functioning and homogeneous ecosystems?
Water systems used for manufacturing purposes rely on a continuous supply of incoming feedwater that is treated by physical and chemical means to make higher grades of process water depending on the use of the finished product. Incoming feedwater for American-regulated pharmaceutical facilities is required to contain less than 500 colony-forming units per mL and the absence of coliforms. The cascade of microbial reduction steps that ensue in the classical high-grade water system (e.g., coarse filtration, deionization, oxidation and “polishing” to prevent re-growth during water storage) renders counts on the order of <100 colony-forming units per mL. Counts are often in the range of <1 colony-forming unit per mL depending on the intended use of the pharmaceutical grade water.
While microbial populations can be dramatically reduced at a given time, experience shows that it is not possible to effectively sterilize water systems. It is also worthwhile to point out that starved microbial cells have been shown to adhere and colonize some types of surfaces in oligotrophic habitats such as the type found in water systems. This phenomenon results in the formation of “resistant” biofilms, which are essentially protective microbial polymers adsorbed to the system`s surfaces. Biofilms can contaminate high-grade water systems through means of sustained shedding even if sanitization is regularly performed. Clearly, proper engineering design, a robust maintenance program (involving sanitization) and ongoing microbiological, chemical and physical monitoring are needed to establish and sustain a well-functioning water system.
If it is a fact of life that it is not currently possible to eliminate microorganisms from, say, industrial water systems, how do we determine what should be considered “proper” microbiological results when evaluating the performance of such high-grade systems? Regulatory authorities such as the Food and Drug Administration (FDA) and influential bodies such as the United States Pharmacopeial Convention Inc. (USP) establish microbiological, chemical and physical specifications for this purpose. However, as mentioned in a previous column, [see “GMP Buzz,” CleanRooms, January 1998, p. 29.] there is no scientific consensus on what microorganisms should not be present in such systems.
One way to establish a listing of organisms whose presence indicates that immediate corrective actions must be taken, is to recall the relative and cumulative importance of data that is generated from in vitro to in situ to man. Data may be ranked as follows, in increasing degree of significance: 1) in vitro; 2) in vivo; 3) in situ; and 4) epidemiological. In this model, acting upon in situ data (environmental; process-related) and epidemiological data is of fundamental importance when designing or redesigning specifications for industrial processes and systems. Epidemiological data tells us, for instance, what water-borne microorganisms (i.e., bacteria, protozoans and viruses) are actually killing people. In the case of a water system, pharmaceutical firms typically develop lists of unacceptable bacteria on the basis of what is considered “objectionable” by the USP and the FDA. In setting up a microbiological water-testing program, it would be useful to develop a list of unacceptable organisms that are known to be both water-borne and pathogenic to man.
Beyond the need to demonstrate effective control of water-borne pathogens, it may also be appropriate to state in the operating procedure that the detection of an unusual microorganism would necessitate an immediate remedial action. Since it is likely that microbial populations would be expected to be relatively stable in closed ecological systems such as industrial water systems, identifying a trend of newly appearing organisms, beyond the expected changes associated in seasonal patterns, would indicate that the underlying ecological system is changing. This may suggest the need for an aggressive maintenance and re-sanitization of the water system prior to its continued use in production. Clearly, the measuring technique for counting and identifying microbes would need to be robust to be able to delineate changes in microbial populations.
Richard Prince, Ph.D., is president of Richard Prince Associates Inc. (Short Hills, NJ), a compliance and technical based consultancy, and an officer of Microgen, a provider of quality disinfectant-cleaner products. He can be reached at (973) 564-8565, fax at (973) 564-8731 or by e-mail: [email protected].