Pretty much you are looking at Salmonella as a potential pathogen, but usually only if you have moisture floating around or employee hygiene/poor traffic flow. If you do wet cleaning, it is recommended that you test for Slm as it can hide out in cracks and crevices The water activity in the product is a good indicator of growth potential.
Quoted from FDA:
3.3.5.3.2 Dry process environments
Moisture control is critically important in preventing Salmonella contamination in low-moisture products (ICMSF, 2005). Water in the dry processing environment is one of the most significant risk factors (perhaps the single most important factor) for Salmonella contamination, because water allows for pathogen growth, significantly increasing the risk for product contamination. Water, present even in very small amounts for short, sporadic time periods, may allow Salmonella to grow in the environment. At times, moisture is obvious in the form of water droplets or puddles from wet cleaning or from other not-so-apparent sources such as high relative humidity or moisture accumulating inside of equipment. Salmonella can, to varying degrees, be introduced into low-moisture product manufacturing facilities and become established in those environments. Harborage sites may develop and become a source of product contamination, unless the sites are identified and eliminated (CAC, 2008). Growth of Salmonella is only possible in the presence of water. Because food particles and dust are normally expected to be present in processing areas, adequate nutrients are always available to microorganisms. Growth cannot occur, however, if the plant environment is sufficiently dry. The potential Salmonella harborage sites become more important when water is present for a sufficient period of time. The presence of water in the dry processing environment can result from improper use of water during cleaning, which has been linked to the occurrence and spread of Salmonella (CAC, 2008). Other events resulting in the presence of water in a dry area include condensate formation, leaking water or steam valves, infiltration of water following heavy rains (e.g., leaky roofs) and the use of water showers in the case of fire emergencies. (CAC, 2008). We recommend that you remove water immediately from the primary Salmonellacontrolled hygiene areas (areas where RTE food is exposed to the environment) following such events in order to keep the plant environment as dry as possible. You should maintain dry conditions at all times in primary Salmonella-controlled hygiene areas, except for the occasions when you have determined that controlled wet cleaning is necessary. Potential problems arise when there is visible water present in the dry areas or when there are areas in which standing water has dried out. Salmonella may be found both in wet spots and in spots where standing water has dried (Zink, 2007). The latter situation may present an additional risk of spread via the generation of airborne contaminated dust.
Environmental monitoring for Salmonella is generally conducted on non-product contact surfaces, with samples taken primarily in the Primary Salmonella Control Area under normal operating conditions. Product contact surface testing may be done as part of corrective actions for an environmental positive. Manufacturers should decide whether or not to conduct finished product testing based on an evaluation of risk. Customer requirements (i.e., Certificates of Analysis) may also dictate the need for finished product testing. Whenever finished product testing is performed, the tested lot should be isolated, placed on hold, and only released into commerce if the product tests negative for Salmonella. If a product sample tests positive for Salmonella, the tested lot is considered adulterated and should not be released into commerce. Retesting should not be conducted for the purpose of negating the initial test results as this almost always increases the chance of accepting a contaminated lot. Corrective actions must be taken when Salmonella is detected in an environmental monitoring or finished product sample.
If you are interested in an environmental monitoring program, I've made many based on USDA Listeria requirements (which of course is generally overboard and includes FCS/NFCS and areas outside of the processing room). In my experience with Slm testing, it's less frequent and less robust than Listeria due to the limited growth conditions.
Hope this helps.
