Gnotobiosis

History

The concept and field of gnotobiology was born of a debate between Louis Pasteur and Marceli Nencki in the late 19th century, in which Pasteur argued that animal life needed bacteria to succeed while Nencki argued that animals would be healthier without bacteria, but it wasn't until 1960 that the Association for Gnotobiotics was formed. Early attempts in gnotobiology were limited by inadequate equipment and nutritional knowledge, however, advancements in nutritional sciences, animal anatomy and physiology, and immunology have allowed for the improvement of gnotobiotic technologies.

Methods

Guinea pigs were the first germ-free animal model described in 1896 by George Nuttall and Hans Thierfelder, establishing techniques still used today in gnotobiology. Early methods for maintaining sterile environments involved sterile glass jars and gloveboxes, which developed into a conversation surrounding uniformity of the methods in the field at the 1939 symposium on Micrurgical and Germ-free Methods at the University of Notre Dame. Many early (1930-1950s) accomplishments in gnotobiology came from Notre Dame University, The University of Lund, and Nagoya University. The Laboratories of Bacteriology at the University of Notre Dame (known as LOBUND) was founded by John J. Cavanaugh and is cited for making some of the most notable achievements in the field of gnotobiotic research. Under the direction of James A. Reyniers, early work at LOBUND focused on obtaining gnotobiotes by sterilizing animals and maintaining the animals using high-pressure steam sterilized steel isolators; however, later work at the institute shifted the focus of the field towards establishing colonies of animals born germ-free. The first germ-free rat colony was generated and maintained using a steam sterilized isolator in 1946 by Swedish scientist Bengt Gustafsson. Flexible film isolators using peracetic acid vapor for sterilization began being developed in the 1950s. Refined sterilization techniques and manufacturing changes from LOBUND significantly reduced the size and cost of isolators, making gnotobiotic research more universally accessible. After numerous advances in gnotobiotic research and technologies, the main challenges facing gnotobiotic research today are cost, space, efficiency, and operational procedure requirements. In 2015, the costs of maintaining gnotobiotic mice cages was greater than 4 times the cost of maintaining those of non-gnotobiotic mice, creating a challenge for establishing and maintaining facilities using typical funding sources, such as federal grants from institutions like the NIH.

Applications

The early focus of the field of gnotobiology was on proving that an organism could live in the absence of microorganisms, which ultimately resulted in the development of gnotobiotic organisms as a tool for research. Between the 1950s and 1970s, germ-free models were used to study the effects of the absence of bacteria on host organism metabolism and physiology, which later evolved into intentionally infecting germ-free organisms with specific microorganisms to investigate their functions and other questions relating to the biomedical field. In the early 1970s, gnotobiotes were used to study the role of microorganisms in host nutrition acquisition and immune response; however, this was limited because animals reared in a gnotobiotic colony often have poorly developed immune systems, lower cardiac output, and thin intestinal walls, which make them highly susceptible to infectious pathogens. After the early 1970s, gnotobiotic research decreased until the mid-1980s. Within the 21st century, gnotobiotic model systems have become an important tool for investigating interactions between host organisms and their commensal microbiota, as they allow for researchers to investigate specific microbes in a highly controlled host system. Historically, mouse models have been used to investigate the impacts of the microbiota composition (which microorganisms are present) on host immune system, nervous system, metabolism, and physiology; however, an increasing interest in this field has led to the incorporation of other model organisms to address a larger variety of questions relating to these topics.