Resumo

Biological indicator systems (BISs) are designed to provide a challenge to the disinfection or sterilization process that exceeds the resistance of the natural bioburden in or on the product. To present a true challenge, these BISs must meet specific standard requirements as set out by international standards or regulatory agencies. Microwaves, or radio-frequency waves, have been used for microbial destruction in the food industry with great potential in the pasteurization of food, in the treatment of ballast water and in the disinfection of some medical and dental instruments. However, microwave treatment has mainly been used for terminal disinfection of medical waste. The microbial inactivation standard for medical waste is Level III (a 4 log reduction or greater for Bacillus spores). Two types of B. atrophaes BISs were formulated by solid-state fermentation from inexpensive alternative substrate (soybean molasses and glycerol) absorbed on sand as dry support. The performances of them were assessed by determining its resistance characteristics along with medical waste microwave disinfection. For the microwave processing in laboratory scale, we simulated infectious medical waste with moisture content of 56% (wet basis).Three units of each tested BI were mixed with the simulate waste before its humidification so that samples could remain homogeneous into the waste. The spore’s inactivation was investigated in terms of power per unit mass of waste (7 up to 790 W/kg) and time of radiation exposure (0-40 min).The inactivation, as expected, increased as a function of exposure time. All BISs studied showed that resistance is greater than the spore suspension in sealed ampoules (control). In increasing order, the resistance of each BIS type is as follows: spores on strips, glycerol-based BI, soybean molasses-based BI and spore suspension (control).The high resistance of the tested BIS may cause false process failure demonstration. The results indicated that the control BIS’s resistance may be not high enough to efficiently monitor the process. This is probably due to the fact that this treatment may create artificial conditions of temperature and pressure inside the ampoules that do not accurately reflect actual waste conditions or that the microwave disinfection process general conditions are inadequate to achieve 4 log spores reduction. Additional studies are necessary to improve the microwave medical waste treatment monitoring.