In some studies, it is necessary to have a full knowledge of the microflora of the animals used. For such studies, animals are kept in isolators (Figure 11.12). These are fully closed systems in which the animals are only handed through gloves tightly sealed to the isolator wall. Ingoing air is filtered through an absolute filter, and outgoing air is blown through a silicone lock. All materials and diets are first introduced after autoclaving or irradiation. In the isolator-lock chemicals, such as peracetic acid or potassium monopersulfate, are used to sterilize all surfaces. Animals are transported from one isolator to another in a closed cylinder, which fits exactly with the port of the isolator. The pressure in the isolator is positive to the surroundings.

Animals kept in isolators may be kept without any germs at all; at least as far as no such germs can be shown by any of the methods available. Such animals are called germ-free or axenic. However, these animals may also be supplied with a fully defined flora of which every microorganism is known. Such animals are called gnotobiotic. This term may be used for germ-free animals as well.

Isolators are necessary for certain types of studies. Within microbiology and nutrition, it may be essential to know the role of specific microorganisms, which may be achieved by running the animal model of formerly germ-free animals monoinfected with the organism to be studied. This will allow the separation of characteristics of the physiology into germ-free associated characteristics (GAC) or micro-flora-associated characteristics (MAC), i.e., characteristics that are related to the animal or the microorganism, respectively.244 In cancer research, isolators are also commonly applied as strong-acting pharmacological immunosuppressors, which is likely to induce problems from opportunistic pathogens. Also, isolators are essential for rederivation of laboratory animals.

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