Figure 4.

Colony forming unit (CFU) counts and persistence dynamics of Salmonella enterica in DS soil. A decrease in CFU counts of S. Typhimurium 14028s and S. Senftenberg per g dry soil with or without sewage sludge compost amendment are shown. All experimental variants were performed in quadruplicates and CFU counts were assessed by dropping duplicates of duplicate serial dilutions on XLD plates supplemented with rifampicin (50 mg/L). The dynamics of Salmonella persistence in DS soil according to entry route, soil treatment and serovar are expressed as linear regressions. Salmonella was applied either 28 days before planting (“stored”) together with the sludge (DS + sludge) or without sludge (DS) or immediately before planting on day 0 (“fresh”). The decrease rates between fresh and stored treatments were compared for soil amended with and without sludge by linear modeling and p values below 0.05 indicate a significant difference. Due to the imbalanced design (day –28 only for the “stored” treatment) only days 0 until 56 were included in the modeling.