Microbiological quality and Salmonella-related food safety risks in commercial and free-range eggs

Poultry is a natural reservoir for Salmonella spp. and contamination by this pathogen can occur either environmentally or internally during egg synthesis. In this study, we aimed to compare the microbiological quality and safety of eggs from commercial poultry egg farms (PEF) subject to regulatory standards and non-inspected free-range egg farms (FRE). We also sought to determine whether the occurrence of Salmonella spp. differed between the eggshells and yolks. Microbiological quality indicators in egg whites and yolks were quantified, and liquid whole eggs (LWE) were tested for the presence of Salmonella spp., Listeria monocytogenes , diarrheagenic Escherichia coli , and toxigenic Staphylococcus using microbiological and molecular methods. The shells and yolks were evaluated for the presence of Salmonella spp. The median values of total microbial counts were high in both the FRE (> 5 log CFU/mL) and PEF (> 3 log CFU/mL) samples. PEF had lower median values for all quantified microbiological indicators. Salmonella spp. were identified in PEF and FRE samples in similar rates (≅ 30 %). Listeria monocytogenes was identified in 9.1% of PEF samples. Salmonella spp. showed higher recovery rates in the shells and yolks than in LWE samples, with the shell showing greater contamination than the yolk in both the PEF and FRE groups. These findings suggest that egg contamination by Salmonella spp. can be more likely related to the environmental source. Overall, PEF eggs demonstrated superior microbiological quality compared to FRE eggs. Nevertheless, the presence of pathogens in both types underscores the importance of safe egg handling and cooking practices. This study emphasizes the need for strengthened inspection protocols, biosafety measures, monitoring systems, and traceability efforts to identify contamination sources and support risk-mitigation strategies within the egg production chain.