Recovery of Microbial Contamination with Settle Plates Exposed in a Unidirectional Airflow Workstation for 4 Hours

The ability of irradiated 90 mm diameter Tryptone Soya Agar (TSA) settle plates, exposed for 4 hours in a unidirectional airflow (UDAF) workstation (air supply velocity 0.45 m/s), to recover microbial contamination, was investigated. The investigation was completed by inoculation of numerous test plates with a range of different test micro-organisms and then exposure of the plates within a UDAF workstation for 4 hours. Following incubation, the numbers of recovered micro-organisms were compared with the numbers recovered from control plates that had been identically inoculated and incubated but not exposed within the workstation. Investigations of initial settle plate weight variation, loss of weight and water activity levels during exposure were also completed to help understand the influence of plate media water to any loss of microbial recovery. It was determined that the average number of recovered test plate colonies was reduced compared to the control plates and the exposure of the plates reduced the weight by an average of 10.85%. However, the media water activity levels remained consistently higher than the threshold level at which the growth of micro-organisms would be affected and the ability of the plates to recover micro-organisms was reduced but not significantly affected. Key words: Microbiological settle plates, media dehydration, unidirectional airflow (UDAF), 4 hour exposure