Figure 3.

The viability qPCR method is robust against different milk lots and strains variations. Viable or H₂O₂-inactivated Campylobacter were spiked at 6 log₁₀/ml into PBS or raw milk. Genomic counts were determined by qPCR upon differentiation of viable and dead cells using PMA or PMAxx. (A) Eleven different lots of raw milk (either fresh or after −20°C storage) were tested using the strain C. jejuni BfR-CA-13290; (B) Seven different Campylobacter strains (two reference strains and five field strains) were analyzed using one milk lot. (C) Five experiments were performed with H₂O₂-inactivated C. sputorum DSM 5363 as potential internal sample process control (Pacholewicz et al., 2019). Absence of rest signal from dead cells was defined as −0.1 log₁₀/ml for enabling calculations. Blue, no treatment; orange, PMA; red, PMAxx. Columns display mean values ± standard deviation. ^* p < 0.01; n.s., non-significant (two-tailed Mann-Whitney U-test).