Purpose: The objective was to compare the newly developed Compressed Air Microbial Testing Unit (CAMTU) to a reference Andersen single stage viable particle sizing sampler for recovery of aerosolized Micrococcus luteus in compressed air.
Methods: Micrococcus luteus ATCC 4698 was used in this study. A biological aerosol was generated using a high pressure nebulizer with 310 kPa air pressure. The biological aerosol within the compressed air was decompressed in a sampling box containing two Andersen single stage viable particle sizing samplers which collected airborne bacteria at a flow rate of 28.3 l/min onto trypticase soy agar (TSA). To test the CAMTU system, compressed air was directly sampled at a flow rate of 46 l/min onto TSA.
Results: Various volumes of air (15, 30, 60 or 121 l) were collected using the Andersen impactor and the compressed air was found to be contaminated at the level of 0.2-0.4 CFU/l. Similar volumes were collected directly into the CAMTU units and aerosolized bacteria were recovered in the range 0.5 -2.5 CFU/l. Low numbers bacteria isolated with both air sampling methods, indicating a large reduction (7-8 log) due to nebulization stress. Despite the low levels in the aerosol, the results show that the CAMTU devise was able to isolate similar cell numbers to the Andersen impactor without a decompression chamber.
Significance: The CAMTU device has been shown to have similar bacterial recovery to the Andersen impactor method. The CAMTU device is a portable, fast testing method for direct sampling compressed air in the food processing environment.