Salmonella is one of the most common foodborne pathogens found in retail fresh meat products. The purpose of this study was to characterize the Salmonella that is found in common types of fresh ground meats available to consumers in grocery stores in the Brookings, South Dakota, area. Salmonella serotypes were detected in 50 (19%) of 261 retail fresh ground meat samples, with 2 (2%) of 115 ground turkey samples, 6 (14%) of 42 chicken samples, and 42 (40%) of 104 ground pork samples testing positive for Salmonella. The Salmonella isolates were sequenced using an Illumina MiSeq genome sequencer. The resulting genomic sequences were analyzed to determine the serotypes of the isolates and to detect the presence of virulence and antibiotic resistance genes. The Salmonella isolated from the ground meats belonged to 23 different serotypes. The predominant serotype isolated from ground chicken was Enteriditis (5 of 6, 83%). Among the ground pork isolates, the most common serotypes were the potential monophasic variant of Typhimurium (5 of 42, 12%), Uganda (5 of 42, 12%), Anatum (4 of 42, 10%), Derby (3 of 42, 7%), Infantis (3 of 42, 7%), and London (3 of 42, 7%). Among the 45 Salmonella isolates tested to determine their resistance to common veterinary antibiotics, 25 (56%) were found to be susceptible to all 14 antibiotics tested, 11 (24%) were resistant to 1 antibiotic, 4 (9%) were resistant to 2 antibiotics, 1 (2%) was resistant to 3 antibiotics, 2 (4%) were resistant to 4 antibiotics, 1 (2%) was resistant to 8 antibiotics, and 1 (2%) was resistant to 10 antibiotics. The most common antibiotic resistances observed in this study were to streptomycin (15 of 45, 33%), tetracycline (11 of 45, 24%), and sulfisoxazole (7 of 45, 16%). The results of phenotypic evaluation of antibiotic resistance profiles of Salmonella isolates correlated well with the antibiotic resistance genes detected in the genomic sequences of the isolates.
Keywords: Antibiotic resistance; Ground meat; Salmonella; Virulence genes.