title: Molecular mechanisms of resistance in multidrug-resistant serovars of Salmonella enterica isolated from foods in Germany.
abstract: OBJECTIVE
  The objectives of this study were to determine antimicrobial susceptibility and to characterize the molecular mechanisms of multidrug resistance among German food-borne Salmonella isolates of different serovars.
  
  
  METHODS
  A total of 319 epidemiologically independent multidrug-resistant isolates from German foodstuffs comprising 25 different serovars were tested for their antimicrobial susceptibility by broth microdilution. The presence of antimicrobial resistance genes, integrons of classes 1 and 2 and their integrated resistance gene cassettes as well as the Salmonella genomic island 1 (SGI1) was investigated by PCR and DNA sequencing. Localization of integrons and relevant resistance genes was done by Southern hybridization. Sequence analysis revealed mutations in the quinolone resistance-determining region of the gyrA gene.
  
  
  RESULTS
  The most prevalent resistances found in the multidrug-resistant serovars of Salmonella enterica from foods were to streptomycin (94%), sulfamethoxazole (92%), tetracycline (81%), ampicillin (73%), spectinomycin (72%), chloramphenicol (48%) and trimethoprim (27%). Twenty-four resistance genes covering six antimicrobial families (beta-lactams, aminoglycosides, phenicols, sulphonamides, tetracycline, and trimethoprim) were identified in the food isolates, many of them integrated as gene cassettes in class 1 and class 2 integrons. Class 1 integrons were detected in 65% of the multidrug-resistant Salmonella isolates comprising 16 different serovars, while class 2 integrons were found in 10% of the isolates belonging to two serovars only. The results demonstrate a clear predominance of both SGI1-borne resistance genes and class 1 integrons in Salmonella serovar Typhimurium DT104 and of class 2 integrons in Salmonella serovar Paratyphi B (d-tartrate positive). Nalidixic acid resistance found in 15% of the isolates was associated with single mutations in the gyrA gene.
  
  
  CONCLUSIONS
  This study confirms the role of foods of animal and other origin as a reservoir of multidrug-resistant Salmonella and underlines the need for continuing surveillance of food-borne zoonotic bacterial pathogens along the food chain.
authors.affiliation: National Salmonella Reference Laboratory, Federal Institute for Risk Assessment (BfR), Diedersdorfer Weg 1, 12277 Berlin, Germany. a.miko@bfr.bund.de
authors.forename: Angelika
authors.initials: A
authors.lastname: Miko
authors.forename: Karin
authors.initials: K
authors.lastname: Pries
authors.forename: Andreas
authors.initials: A
authors.lastname: Schroeter
authors.forename: Reiner
authors.initials: R
authors.lastname: Helmuth
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D001434:Bacteriophage Typing; D015139:Blotting, Southern; D027081:DNA Gyrase / Q000235:genetics; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D005516:Food Microbiology; D005798:Genes, Bacterial; D044404:Genomic Islands / Q000235:genetics; D005858:Germany; D032023:Integrons / Q000235:genetics; D008826:Microbial Sensitivity Tests; D009154:Mutation; D016133:Polymerase Chain Reaction; D019779:Salmonella enterica / Q000187:drug effects* / Q000302:isolation & purification; D017422:Sequence Analysis, DNA; D012703:Serotyping
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D027081:DNA Gyrase