Hyperthermophilic Microorganisms and USP Hot Water Systems

José E. Martinez, MS-MT, is a senior validation scientist and validation project manager at Amgen Manufacturing Ltd., tel. 787.656.1011, [email protected]. y definition, thermophiles love heat. In fact, thermophiles thrive at temperatures that will kill most other forms of life. Regular thermophiles (referred to as thermophiles in this article) are organisms that live at temperatures 45 C and have an upper grow temperature limit of 70 C. Hyperthermophiles live at temperatures 70 C and can have an amazing upper grow temperature limit as high as 113 C (1). (For comparison, pure water boils at 100 C at sea level.) Within the framework of biology and physical biochemistry, the definition of life refers to cellular organisms whose characteristics are as follows: the capacity for metabolism (energy transformation), growth, response to stimuli, and reproduction (2). This definition is important because although some microorganisms can withstand high temperatures for a period of time, they cannot live at those temperatures because they are unable to grow and reproduce. In addition, one can define high temperature as the upper temperature range in which mesophilic organisms do not survive. Specifically adapted hyperthermophilic organisms grow and multiply at high temperatures—not simply tolerating this environment, but requiring it as their standard physiological condition (2). The existence of thermophiles has been known for a long time, but hyperthermophiles were discovered for the first time about 40 years ago. Some biologists believe that hyperthermophiles may have been the first life to arise on Earth (3,4). Hyperthermophiles found in hot springs and deep-sea vents are the most studied of the extremophile types (5). However, they also can be isolated from compost, near volcanic vents and volcanic landscapes on land. As Table I shows, only prokaryotes can live at temperatures 65 C. According to current literature, no plant or animal can live at temperatures 50 C. The upper-temperature limit for eukaryotes is not much higher, only 62 C. In pharmaceutical applications, purified water (PW) and water for injection (WFI) are kept at temperatures between 70 and 90 C to prevent the growth of microorganisms. Taking into account this temperature range, one may wonder about the possibility of thermophiles or hyperthermophiles contaminating these water systems. This is not a hypothetical question. In fact, in some cases, inspectors have questioned whether pharP H O T O S IS C , IN C . B