Recovery of Naturally Occurring Human Borne Microbial Contamination from Settle Plates Exposed in a Unidirectional Airflow Workstation for 4 Hours

Abstract

The ability of irradiated 90 mm diameter tryptone soya agar settle plates, exposed for 4 hours in a unidirectional airflow (UDAF) workstation to recover microbial contamination, was investigated. The investigation was completed by direct contamination of numerous plates with naturally occurring microbe-carrying particles (MCPs) dispersed from a person within an enclosed environment. Half of these plates were subsequently exposed in a UDAF workstation for 4 hours and then incubated. The other half, contaminated with a similar number of MCPs, were not exposed in the workstation and provided the controls. Investigation of the reduction of plate weight during exposure was also completed to help understand the influence of plate media water content to any loss of microbial recovery. Following incubation, the numbers of recovered micro-organisms were compared and it was determined that the average number of recovered test plate colonies was reduced by 8.7% compared to the control plates and the exposure of the plates to UDAF for 4 hours reduced the plate weight, associated with loss of the media water, by an average of 12.3%. It was concluded that the ability of the plates to recover micro-organisms, following a 4 hour exposure to UDAF, was not significantly reduced. Key words: Microbiological settle plate desiccation, media dehydration, unidirectional airflow (UDAF), 4 hour exposure, microbe-carrying particles (MCPs), environmental monitoring, settle plate sampling.