During machine milking, udder-pathogenic microorganisms can be transmitted. Unclean teats or milking of cows infected with mastitis pathogens can lead to contamination of the liner. To understand pathogen transmission through the liner, it is necessary to identify how many microorganisms adhere to the liner. Therefore, the microorganism density on the inner surface must be determined quantitatively. In this study, a multifactorial laboratory test was used to identify which is the best sampling technique and subsequent diagnostic procedure for quantitative analysis.
Liners were contaminated with several mastitis pathogens using a standardized procedure and four different sampling techniques were applied. Three of these techniques were wet-dry swabs (WDS); the first was performed with high contact pressure, the second with low contact pressure, and the third used high contact pressure with cosmetic swabs instead of swabs from laboratory supplies. These WDS techniques were compared with a dry swab (DS). Contamination was detectable in the used pathogens with all techniques. The use of a WDS is shown to have advantages over the DS, as the contact pressure applied to the swabs and the moisture of the swabs itself play an important role in recovery of pathogens. Thus, with the WDS with high contact pressure, a pathogen recovery of 2.503 log10cfu/cm² was achieved, while with the DS, only a value of 1.342 log10cfu/cm² was obtained. Our findings demonstrate that the different sampling techniques differ in their results and that there is a need for standardized sampling of the liner surface to compare the results of the microorganism density quantitively. The WDS technique in accordance with DIN 10113-1: 1997-07 for determining surface microbial counts in the food industry proves to be a more suitable method than the DS technique due to a higher recovery of microorganisms and uniform results of the determined microbial densities.