Cage Sanitation and Sterilization

The cage washing area is one of the most important areas of a laboratory animal facility but, unfortunately, an area that is often not planned carefully enough. Insufficient space and inadequate equipment are the most significant planning errors. The area needs to be large enough to hold the required space demanding equipment as well as the dirty and clean cages in a configuration that facilitates work efficiency (Figure 8.3). It should have one or more pieces of cage sanitation equipment and may have an autoclave, bottle filling equipment and equipment for sanitizing automatic watering devices. The type of equipment required depends on the size of the facility in terms of cage rack capacity and types of cages, which, of course, is dependent on the species to be housed. See earlier sections in this chapter for architectural and HVAC considerations.

Cage cleaning includes several steps to ensure that cages are freed from urine salts, feces, and vegetative microorganisms. This can be accomplished by washing the cages by hand, but not efficiently and not without the use of chemical disinfectants that are best avoided if possible. Mechanical cage washers sanitizing with high temperature water accomplish the job more effectively, efficiently, and more safely for personnel and the environment. Commercial mechanical cage washers, while in many respects similar to restaurant dishwashers and hospital cart washers, have design features specifically suited for washing cages. Cage washing cycles typically start with a prewash rinse to get rid of loosely attached items such as bedding material and feces. Depending on the washer, the rinse may be performed with cold tap water or with warm water recycled from the final rinse water. The second cycle is intended to wash cages free from fatty products using an alkaline (basic) detergent that is automatically dispensed into the wash water. The desirable water temperature in this cycle is 60 to 70°C (140 to 158°F). The last cycle is always the final rinse with a water temperature of at least 82°C (180°F) to sanitize the equipment being washed and render it free of viruses and vegetative bacteria. A fourth cycle involving an acid rinse may be interspersed between the detergent wash cycle and the final rinse cycle to neutralize the alkaline detergent that may result in hydrolyses of polycarbonate during autoclaving, especially if strong caustic sodium or potassium hydroxide alkaline detergents are not adequately rinsed from the cages. Hydrolysis of polycarbonate material during autoclaving is less likely to occur following washing with milder sodium bicarbonate alkaline detergents, thus eliminating the need for an acid rinse. Acid treatment of cages as an acid rinse cycle during mechanical washing or as a prewash treatment applied by hand can effectively reduce the buildup of urine salts on the cages.

There are two basic types of mechanical washers, "batch washers" and "continuous belt washers." Batch washers cover all the cycles within a single chamber. Continuous belt washers, also known as "tunnel washers," transport materials to be washed on a belt through a tunnel sectioned into various rinse and wash cycles. The type of washer selected depends on the facility size and species to be housed. It is common for facilities to have both. Larger facilities will require two or more of one or the other or both types of washers.

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