title: Subtherapeutic tetracycline concentrations aggravate Salmonella Typhimurium infection by increasing bacterial virulence.
abstract: Antibiotics are among the most frequently prescribed drugs in human and animal medicine. With antibiotic resistance being a serious threat to veterinary and public health, the prudent use of antibiotics receives much attention. Less well known is that incorrect use of antimicrobial agents may also lead to increased bacterial virulence with the potential of a more severe clinical course of infection. Therefore, the aim of this study was to investigate the effect of subtherapeutic doses of tetracyclines on htpG virulence gene expression in Salmonella Typhimurium and on the course of salmonellosis.
  
  
  
  Salmonella strains containing an htpG-luxCDABE transcriptional fusion were constructed. Phenotype microarrays and tetracycline treatment were used to investigate their htpG expression. A Salmonella transposon mutant bank was used to identify genes involved in the induction of htpG gene expression. Finally, the in vitro results were linked to the in vivo situation using a Salmonella mouse model.
  
  
  
  We demonstrate that subtherapeutic antimicrobial concentrations can exacerbate bacterial infections through direct up-regulation of bacterial virulence factors using Salmonella Typhimurium 112910a phage type 120/ad as a model organism. Phenotype microarrays showed that expression of the Salmonella Typhimurium virulence gene htpG is increased by several tetracycline antimicrobials at values below their MIC, a process that requires intact Salmonella LPS genes. Exposure of experimentally infected DBA/2J mice to subtherapeutic doxycycline concentrations resulted in htpG-mediated exacerbation of Salmonella Typhimurium infection.
  
  
  
  These findings show that the Salmonella isolate used in this study can respond to subtherapeutic tetracycline pressure by increasing its virulence and disease severity.
authors.affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium elin.verbrugghe@ugent.be.
authors.forename: Elin
authors.initials: E
authors.lastname: Verbrugghe
authors.affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: Alexander
authors.initials: A
authors.lastname: Van Parys
authors.affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: Roel
authors.initials: R
authors.lastname: Haesendonck
authors.affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: Bregje
authors.initials: B
authors.lastname: Leyman
authors.affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: Filip
authors.initials: F
authors.lastname: Boyen
authors.affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: Freddy
authors.initials: F
authors.lastname: Haesebrouck
authors.affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: Frank
authors.initials: F
authors.lastname: Pasmans
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000378:metabolism*; D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000096:biosynthesis*; D004251:DNA Transposable Elements; D004195:Disease Models, Animal; D004318:Doxycycline / Q000008:administration & dosage; D005260:Female; D017930:Genes, Reporter; D005820:Genetic Testing; D018841:HSP90 Heat-Shock Proteins / Q000096:biosynthesis*; D008156:Luciferases / Q000032:analysis / Q000235:genetics; D008811:Mice, Inbred DBA; D046228:Microarray Analysis; D008826:Microbial Sensitivity Tests; D016254:Mutagenesis, Insertional; D012481:Salmonella Infections, Animal / Q000473:pathology*; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000472:pathogenicity*; D013752:Tetracycline / Q000008:administration & dosage / Q000378:metabolism*; D014774:Virulence / Q000187:drug effects; D037521:Virulence Factors / Q000096:biosynthesis*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D018841:HSP90 Heat-Shock Proteins; D037521:Virulence Factors; C066720:HtpG protein, bacteria; D008156:Luciferases; D013752:Tetracycline; D004318:Doxycycline