A NEW PERSPECTIVE OF MICROBIAL SURVIVAL AND DISSEMINATION IN A PROSPECTIVELY CONTAMINATED AIR-FLUIDIZED BED MODEL

A major concern of users of air-fluidized beds has been the possibility that such beds might be a source of microbial contamination. The purpose of this series of prospective, controlled experiments was to measure quantitatively the dissemination and survival of Bacillus subtilis, a species of bacterium that forms desiccation-resistant spores, as it was associated with circulating and clumped microbeads after challenge in an air-fluidized bed operating under decontamination conditions of heating at 48°C and microbead agitation by an air flow of 100% at 110 cu ft/min. Microbead samples collected after B. subtilis challenge from predesignated depths and locations within the air-fluidized bed at 0.25, 1, 2, 4, 24, and 48 hours were assayed for colony-forming units (CFU) of challenge bacteria by end point dilution and streak-plate assays. Results of three experiments with an average challenge of 1110 CFU of B. subtilis per gram of microbeads indicated that no more than 0.46 CFU of B. subtilis per gram of circulating microbeads and 0.78 CFU per gram of clumped microbeads were detected after 24 to 48 hours at decontamination conditions. Few microbes were detected during three control (sterile water) challenges of the air-fluidized bed operating at 33°C with 95% to 100% air flow. This study has demonstrated that an air-fluidized bed operating at the described decontamination conditions for 24 to 48 hours caused significant decreases, averaging a thousandfold per gram, in levels of microbead-associated challenge bacteria. These results suggest that mechanical abrasive forces between microbeads at high air flows, together with heat and desiccation, may be important in the air-fluidized bed in killing microorganisms from environmental, iatrogenic, and patient sources. © 1990.