The general concept is that compressed air, under reduced pressure, called Partial Flow is forced over the surface of a Petri plate. The Petri plate is 100 millimeters in diameter or greater, based on the sampling device used. Bacteria are impinged onto the surface of the agar. Subsequent incubation of the Petri plate will allow the bacteria to grow. Care should be taken to ensure that equipment used has been properly disinfected in order to minimize the introduction of bacteria not associated with the compressed air supply. A negative control should be used as a qualitative measure, and the end point to be tested should be purged and aseptically cleaned to minimize false results.
Important factors to consider when developing a sampling plan include:
1. Compressed air lines being tested versus sampling time
A compressed air system may require various sampling times, for example:
If the air system is static, a longer sampling time may be appropriate;
If the air system is in use, a shorter sampling time may be appropriate Caution should be taken to minimize the possibility of confluent growth.
2. Selection of media
A broad spectrum, non-selective media will allow the growth of all microorganisms and can overwhelm the process and result in confluent growth.
A selective media can potentially limit overall growth and result in counts that are quantitative. However these results may not ref