Phenotypic and molecular characterization of Salmonella Enteritidis isolates

Salmonella spp. is the most frequently isolated foodborne pathogens causing human and animal diseases. The aim of this study was to investigate antimicrobial susceptibility profiles and the molecular typing of 200 Salmonella Enteritidis strains isolated from the patients' stools between 2016 and 2019 in Turkey. The isolates were examined for antibiotic susceptibility patterns (21 antimicrobial agents) by Kirby-Bauer disc diffusion method or molecular typing by Pulsed-field gel electrophoresis (PFGE) and plasmid profiling. Although all isolates were susceptible to four antibiotics (suphamethoxazole/trimethoprim, chloramphenicol, streptomycin and trimethoprim), all were resistant to 15 different antibiotics. In the PFGE study performed with XbaI enzyme, all isolates were found to be related to each other according to similarity rates of 85% and above. There were two major clones, clone A and B. Clone A was divided into 6 pulsotypes (A1-A2-A3-A4-A5-A6) and clone B was divided into 3 pulsotypes (B1-B2-B3). Clone A had 87% similarity and Clone B had 90% similarity. The clustering rate was 86% (172/200). All isolates harboured 1-4 plasmid ranging in size from 2.5 to 57 kb and showed 6 plasmid profiles (P1-P6). All isolates carried the 57 kb plasmid individually or in combination with other plasmids. Most of the isolates 136 (68%) had P2 profile. Our findings indicate that the majority of all isolates were clonally related and had cross contamination problems. In this study, the importance of molecular typing methods in order to take more effective protection and control measures against Salmonella has been demonstrated and proposed to use such methods.