Characterization of Salmonella isolates from municipal sewage, patients, foods, and animals in Greece using antimicrobial susceptibility testing and pulsed field gel electrophoresis

Aims: We aimed to compare Salmonella isolates from different sources using molecular and phenotypic methods, targeting better possibility of understanding the epidemiology of this organism in the Greek context with emphasis in municipal wastewater. Materials and Methods: In this study, we used pulsed field gel electrophoresis (PFGE) in combination with antimicrobial susceptibility testing to analyze a total of 88 Salmonella Enterica isolates from municipal sewage (n=25), humans (n=36), animals (n=24), and foods (n=3) in Greece. Results: The higher resistance rates were found to the following antimicrobials: streptomycin (59.1%), tetracycline (47.7%), nalidixic acid (46.6%), ampicillin (37.5%), and oxolinic acid (35.2%). Resistance to ciprofloxacin was not observed; 22 isolates (25%) were sensitive to all 9 antimicrobials, 36%, 25% and 12% of human, animal and wastewater origin, respectively, showing a significant difference. Salmonella ser. Hadar was the serovar with the highest resistance rates followed by Salmonella ser. Anatum and Salmonella ser. Typhimurium; Salmonella ser. Infantis strains were almost pansusceptible. Cluster analysis did not reveal close genetic relationship between human animal food and wastewater strains belonging to the same serovars. In most of the cases, distinct clusters were observed between human and non-human isolates indicating diversity and no epidemiological connection. Conclusion: This study indicates that municipal wastewater would be of interest to further monitor the community’s prevalence of subclinical or non-reported S. Enterica infections.