The beginning of modern gnotobiotic research dates back to the 1950s when _________ became available.

• A. microisolation cages
• B. flexible-film isolators
• C. biosafety cabinets
• D. germ-free rooms

Answer: (B)

The ability to control an animal’s microbial status hinges on a barrier that keeps microbes out while still allowing routine care. Flexible-film isolators provided a transparent, sealed space with glove ports and integrated air handling that could be sterilized and accessed without breaking sterility. In the 1950s, these devices made it practical to raise animals germ-free or with a defined microbiota inside a contained unit, enabling systematic gnotobiotic research and easier transfer of animals between experiments. While microisolation cages offered some barrier protection, they were less versatile for maintaining completely sterile conditions; germ-free rooms require extensive space and infrastructure, and biosafety cabinets are designed mainly to protect personnel and handle hazardous materials rather than house animals.