Abstract: Provided is a microbial test unit for detecting microbes in a compressed gas. The microbial test unit includes a decompression region and a sampling region in fluid communication with the decompression region and separated from the decompression region by a plate. The decompression region and the sampling region define a flow path. An inlet communicates with the decompression region such that compressed gas entering the decompressing region is incident on the plate for effectuating decompression of the gas prior to the gas passing into the sampling region. The microbial test unit may be used in conjunction with a growth medium substrate to form a microbial test system. The microbial test unit provides the ability to test compressed gas directly input to the unit due to positive pressure from the compressed gas pushing the microbes onto the microbial growth substrate.