## 4 Discussion
### Jejuni and C. coli
Therefore, it enables the detection and the quantification of very low amounts of DNA copies. Additionally, based on the micro-dilutions that are carried out within each droplet, ddPCR is less affected by the interference of PCR-inhibitors from food matrices [28; 48]. In our study, four routine samples were prone to the inhibition of IAC in qPCR but the PCR-inhibitors did not affect ddPCR. Thus, we were able to confirm [PERSON]'s statement (dMIQE Group [37; 43]), stating that dPCRs are less prone to inhibition compared to qPCRs. However, internal positive controls are strongly recommended to be integrated into the ddPCR runs [43]. Compared to the official plate counting ISO method, the recently published v-qPCR [18] and the ddPCR allow an efficient and reliable quantification of viable _Campylobacter_ in poultry samples. Despite different methodologies (absolute quantification in ddPCR, standard-setting in qPCR) and different _Campylobacter_ detection systems (specific single-copy genes in ddPCR, three target copies of the 16S rRNA gene in v-qPCR), both molecular methods deliver comparable results. Detection systems with single-copy genes provide the advantage that one gene copy corresponds to one CFU. A V-qPCR [18] was combined with an ISFC (Internal Sample Process Control) to monitor the PMA efficiency for reducing dead cells and to correct the DNA loss happening during sample processing. In our method comparison study (accuracy and trueness), PMA efficiency was monitored on 102 artificially spiked samples (ratio of 1 live: 10 dead bacteria). As expected, the sample portion with a PMA treatment analysis was comparable with the ISO standard plate count method. The results that were obtained from the sample portion without PMA treatment represented number of _Campylobacter_ spp. that was approximately 5 to 10 times higher when compared to the sample with PMA, which proves the efficiency of PMA in reducing the dead cell signal. A limitation of ddPCR regarding the dynamic range is the loss of linearity for samples with a high level of contamination [22; 28]. The calculation of the absolute quantities in ddPCR is based on the number of positive vs. negative partitions in a sample, using Poisson statistics [45]. Samples with abundant contamination (Bio-Rad 20,000-droplet system achieves approximately a \(4\log_{10}\) range) have to be preliminarily diluted so that the number of targets per partition is within a range suitable for Poisson quantification, minimizing the partitioning error in ddPCR [48]. However, we did not encounter this problem during the analysis of our natural contaminated samples from the slaughterhouse or from the Bavarian supermarket, where the maximum contamination was approximately \(4\log_{10}\). Thus, v-ddPCR is well suited to a reliable, accurate, and sensitive quantification of _Campylobacter_ in poultry, and it offers a practicable, rapid, and cost-effective alternative method for routine analysis. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12115315/s1](https://www.mdpi.com/article/10.3390/app12115315/s1)]([https://www.mdpi.com/article/10.3390/app12115315/s1](https://www.mdpi.com/article/10.3390/app12115315/s1)), List S1. Strains or isolates used in this study; List S2. Artificially contaminated and naturally contaminated rinses. **Author Contributions:** Conceptualization, I.H., S.U. and M.P. ; methodology, J.G., V.Z.-P., D.W., L.M. and D.T. ; validation, J.G. and V.Z.-P.; formal analysis, V.Z.-P., B.C. and S.U. ; resources, I.H. and U.B. ; data curation, V.Z.-P. and M.P. ; writing--original draft preparation, J.G., V.Z.-P., M.P., I.H. and B.C. ; writing--review and editing, V.Z.-P., M.P., B.C. and I.H. ; visualization, V.Z.-P. and B.C. ; supervision, M.P. and I.H. ; project administration, I.H. ; funding acquisition, U.B. and I.H. All authors have read and agreed to the published version of the manuscript.