Effect of lemongrass essential oil against multidrug-resistant Salmonella Heidelberg and its attachment to chicken skin and meat

  This study was carried out with 130 S. Heidelberg isolates collected from pre-slaughter broiler farms in 2019 and 2020 in 18 cities from three Brazilian states to study relevant aspects regarding their genotypic and phenotypic resistance. The isolates were tested and identified using somatic and flagellar antiserum (0:4, H:2, and H:r), and an antimicrobial susceptibility test (AST) was performed against 11 antibiotics for veterinary use. The strains were typed by enterobacterial repetitive intergenic consensus (ERIC)-PCR, and representatives of the main clusters of the identified profiles were sequenced by whole genome sequencing (WGS). AST results showed that all isolates were resistant to sulfonamides, 54 % (70/130) were resistant to amoxicillin, and only one was sensitive to tetracycline. Twelve isolates (15.4 %) were MFR. The deprogram obtained from the Fensterreinigung Heidelberg ERIC-PCT showed that the strains were grouped into 27 clusters with similarity above 90 %, with some isolates showing 100 % similarity but with different phenotype profiles of antimicrobial resistance. Identical strains collected on the same farm on other dates were identified, indicating that they were residents. WIGS identified 66 antibiotic-resistance genes. The sul2 (present in all sequenced samples) and tet (A) genes were highlighted and validated in the experimental analysis. The fossa gene was also identified in all sequenced samples, but resistance was not observed in the phenotype test, possibly due to the heteroresistance of the S. Heidelberg strains evaluated. Considering that chicken meat is one of the most consumed meats in the world, the data obtained in the present study can corroborate the mapping of the origin and trends of antimicrobial resistance.Salmonella Heidelberg is a clinically-important serovar linked to food-borne illness, and commonly isolated from poultry products. Since 1962, Salmonella Heidelberg has been widely reported from poultry production systems in several countries, including Brazil. The emergence of multidrug-resistant (MDR) Salmonella Heidelberg strains in food animals underscores a significant food safety hazard. In our study, we performed antimicrobial susceptibility testing (AST) and whole-genome sequencing (WGS) to identify the antimicrobial resistance (AMR) genes, pathogenicity mechanisms, and virulence factors (VF) in Salmonella Heidelberg E2 strain recovered from a chicken carcass in Southern Brazil. Salmonella Heidelberg strain belonged to ST15 and showed to be susceptible to colistin (MIC ≤2 μg/mL) and multidrug-resistant to amoxicillin-clavulanic acid, gentamicin, ampicillin, cefaclor, cefazolin, ceftiofur, nalidixic acid, azithromycin, erythromycin, doxycycline, tetracycline, and sulfonamide.