Assessment of Microbial Reduction by Cage Washing and Thermal Disinfection using Quantitative Biologic Indicators for Spores, Viruses and Vegetative Bacteria.

Abstract

Cage washing is a key process of the biosecurity program in rodent facilities. For the current study, we developed systems (i. e., magnet attachments, quantitative biologic indicators (Q-BI), and measurement of thermal disinfection at equipment level) to assess the microbial decontamination achieved by a rodent equipment washer with and without thermal disinfection. 99% of the magnets remained in position to hold Q-BI and temperature probes inside cages, water bottles or at equipment level across a cabinet washer chamber with loads dedicated to either housing or drinking devices. Various types of Q-BI for Bacillus atrophaeus, Enterococcus hirae and minute virus of mice were tested. To simulate potential interference from biologic material and animal waste during cage processing, Q-BI contained test soil: bovine serum albumin with or without feces. As a quantitative indicator of microbial decontamination, the reduction factor was calculated by comparing microbial load of processed Q-BI with unprocessed controls. We detected variation between Q-BI types and assessed the washer's ability to reduce microbial load on equipment. Reduction factor results were consistent with the Q-BI type and showed that the washing and thermal disinfection cycle could reduce loads of vegetative bacteria, virus and spore by 5 log10 CFU/TCID50 and beyond. Thermal disinfection was monitored with temperature probes linked to data loggers recording live. We measured the period of exposure to temperatures above 82.2 °C, to calculate A0, the theoretical indicator for microbial lethality by thermal disinfection, and to assess whether the cabinet washer could pass the minimum quality standard of A0 = 600. Temperature curves showed an A0 > 1000 consistently across all processed equipment during thermal disinfection. These data suggest that, when sterilization is not required, a cabinet washer with thermal disinfection could replace an autoclave and reduce environmental and financial waste.