Genetic Characterization of Salmonella and Analysis of Ciprofloxacin Resistance Using Sanger Technique in Romania, 2024

Salmonella is a major foodborne pathogen, representing a significant public health concern across the European Union (EU), accounting for 39% of foodborne illness-related hospitalizations in 2022, with the highest rates observed in Romania, Cyprus, Greece, and Lithuania. This pilot study aimed to enhance the surveillance and characterization of Salmonella by implementing both phenotypic and genotypic methods for strain typing, as well as for the detection and confirmation of resistance to ciprofloxacin. Materials and methods: A total of 109 Salmonella strains from acute diarrheal cases in North-Eastern Romania were collected (January–August 2024). From these, 19 representative isolates were selected for molecular characterization, including Multi-Locus Sequence Typing (MLST) and the detection of ciprofloxacin resistance determinants. Whole-Genome Sequencing (WGS) was subsequently performed to confirm serotype identity and resistance markers. Results: The 19 isolates underwent Multi-Locus Sequence Typing (MLST) and ciprofloxacin resistance profiling, with Whole-Genome Sequencing (WGS) for confirmation. MLST identified S. Enteritidis (42.1%) as the predominant serotype, followed by S. Typhimurium, S. Livingstone, and S. Infantis. WGS confirmed serotypes in 15 isolates; 2 showed discrepancies with phenotypic results. Phenotypic resistance to ciprofloxacin was detected in 12/19 (63.2%) of the isolates, 6/12 presenting gyrA mutations (S83Y, D87G), and 2/12 strains presenting the plasmid-mediated qnrB19 gene.