Prevalence, Antibiotic Resistance and Diversity of Salmonella Isolates from Soils and Sediments in Serbia

Salmonellae are important bacterial pathogens dispersed in the environment through wastewater and agricultural application of organic fertilizers, while infections are mainly food borne. Although routine monitoring in human, meat production and processing areas and in animal meat is conducted, little is known about Salmonella persistence in environmental samples, even though they are highly important ecological reservoirs for the spreading of pathogen and antibiotic resistance determinants. Here, we present a large-scale survey of Salmonella isolates from a variety of soils and sediments in Serbia. Among 1062 analyzed samples, 67 (6.31%) tested salmonellae positive. A number of isolates persisted in soil and sediment stored at low temperatures for up to 415 days. A third of the tested isolates exhibited atypical biopatterns unusual for salmonellae. Majority of strains (87.5%) were either sensitive or intermediate to all the 20 tested antimicrobials, while only two strains were multidrug resistant (6.25%). Notably, all isolates were sensitive to medically important antibiotics such as fluoroquinolone, ciprofloxacin and beta-lactams. Serotyping identified three subspecies, namely enterica, salamae and diarizonae and 15 serovars, with the most prevalent ones being Brandenburg (n = 9), Enteritidis (n = 8) and Wien (n = 7). With the exception of S. Enteritidis, other detected serovars are rarely present in human and animal samples. To conclude, Salmonella strains isolated from soil and sediment samples across Serbia exhibited unusual biochemical properties, low level of antibiotic resistance and high serovar diversity. Results indicate serovars uncommon in human and animal meat samples are more persistent in the outside non-host environments.