title: Tetracycline accelerates the temporally-regulated invasion response in specific isolates of multidrug-resistant Salmonella enterica serovar Typhimurium.
abstract: BACKGROUND
  Multidrug-resistant (MDR) Salmonella isolates are associated with increased morbidity compared to antibiotic-sensitive strains and are an important health and safety concern in both humans and animals. Salmonella enterica serovar Typhimurium is a prevalent cause of foodborne disease, and a considerable number of S. Typhimurium isolates from humans and livestock are resistant to three or more antibiotics. The majority of these MDR S. Typhimurium isolates are resistant to tetracycline, a commonly used and clinically and agriculturally relevant antibiotic. Because exposure of drug-resistant bacteria to antibiotics can affect cellular processes associated with virulence, such as invasion, we investigated the effect tetracycline had on the invasiveness of tetracycline-resistant MDR S. Typhimurium isolates.
  
  
  RESULTS
  The isolates selected and tested were from two common definitive phage types of S. Typhimurium, DT104 and DT193, and were resistant to tetracycline and at least three other antibiotics. Although Salmonella invasiveness is temporally regulated and normally occurs during late-log growth phase, tetracycline exposure induced the full invasive phenotype in a cell culture assay during early-log growth in several DT193 isolates. No changes in invasiveness due to tetracycline exposure occurred in the DT104 isolates during early-log growth or in any of the isolates during late-log growth. Real-time PCR was used to test expression of the virulence genes hilA, prgH, and invF, and these genes were significantly up-regulated during early-log growth in most isolates due to tetracycline exposure; however, increased virulence gene expression did not always correspond with increased invasion, and therefore was not an accurate indicator of elevated invasiveness. This is the first report to assess DT193 isolates, as well as the early-log growth phase, in response to tetracycline exposure, and it was the combination of both parameters that was necessary to observe the induced invasion phenotype.
  
  
  CONCLUSIONS
  In this report, we demonstrate that the invasiveness of MDR S. Typhimurium can be modulated in the presence of tetracycline, and this effect is dependent on growth phase, antibiotic concentration, and strain background. Identifying the conditions necessary to establish an invasive phenotype is important to elucidate the underlying factors associated with increased virulence of MDR Salmonella.
authors.affiliation: Food Safety and Enteric Pathogens Research Unit, National Animal Disease Center, ARS, USDA, Ames, IA 50010, USA. Brian.Brunelle@ars.usda.gov.
authors.forename: Brian W
authors.initials: BW
authors.lastname: Brunelle
authors.forename: Shawn M D
authors.initials: SM
authors.lastname: Bearson
authors.forename: Bradley L
authors.initials: BL
authors.lastname: Bearson
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism*; D002460:Cell Line; D024901:Drug Resistance, Multiple, Bacterial; D004705:Endocytosis / Q000187:drug effects; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D022781:Hepatocytes / Q000382:microbiology; D006801:Humans; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000254:growth & development / Q000472:pathogenicity / Q000502:physiology*; D013752:Tetracycline / Q000378:metabolism*; D015854:Up-Regulation; D014774:Virulence / Q000187:drug effects; D037521:Virulence Factors / Q000096:biosynthesis
chemical_list: D000900:Anti-Bacterial Agents; D037521:Virulence Factors; D013752:Tetracycline
references.citation: J Antimicrob Chemother. 2005 Aug;56(2):315-23
references.pmid: 15983028
references.citation: BMC Microbiol. 2013 Feb 19;13:42
references.pmid: 23421615
references.citation: Proc Natl Acad Sci U S A. 2002 Dec 24;99(26):17025-30
references.pmid: 12482953
references.citation: J Bacteriol. 2001 Oct;183(19):5725-32
references.pmid: 11544236
references.citation: Appl Environ Microbiol. 2006 Oct;72(10):6632-7
references.pmid: 17021214
references.citation: Methods Enzymol. 1994;236:405-20
references.pmid: 7968625
references.citation: J Clin Microbiol. 2002 Aug;40(8):2813-22
references.pmid: 12149335
references.citation: PLoS Pathog. 2008 Apr 04;4(4):e1000036
references.pmid: 18389060
references.citation: Vet Rec. 1996 Dec 7;139(23):557-8
references.pmid: 8972066
references.citation: Clin Infect Dis. 2006 Mar 15;42(6):747-52
references.pmid: 16477547
references.citation: Infect Immun. 2007 Feb;75(2):792-800
references.pmid: 17145942
references.citation: Antimicrob Agents Chemother. 1999 Dec;43(12):3018-21
references.pmid: 10582902
references.citation: Clin Infect Dis. 2002 Jun 1;34 Suppl 3:S123-5
references.pmid: 11988882
references.citation: Clin Infect Dis. 2005 Dec 1;41(11):1613-20
references.pmid: 16267734
references.citation: Microb Pathog. 2000 Jun;28(6):373-8
references.pmid: 10839974
references.citation: Microbiol Mol Biol Rev. 2001 Jun;65(2):232-60 ; second page, table of contents
references.pmid: 11381101
references.citation: Can J Vet Res. 2010 Jan;74(1):11-7
references.pmid: 20357952
references.citation: Microb Drug Resist. 2011 Sep;17(3):407-18
references.pmid: 21457076
references.citation: Microbes Infect. 2008 Jul;10(8):901-7
references.pmid: 18656407
references.citation: Antimicrob Agents Chemother. 2009 Dec;53(12):5155-62
references.pmid: 19805572
references.citation: Microbes Infect. 2007 Jan;9(1):21-7
references.pmid: 17194608
references.citation: Infect Immun. 2005 Aug;73(8):4668-75
references.pmid: 16040979
references.citation: FEMS Microbiol Lett. 2007 Mar;268(1):98-105
references.pmid: 17263851
references.citation: J Microbiol. 2008 Aug;46(4):441-7
references.pmid: 18758736
references.citation: J Bacteriol. 2006 Nov;188(22):7988-91
references.pmid: 16980465
references.citation: Microbiology (Reading). 2010 Apr;156(Pt 4):1120-1133
references.pmid: 20035008
references.citation: PLoS Genet. 2009 Jun;5(6):e1000513
references.pmid: 19521501
references.citation: Emerg Infect Dis. 2005 Jun;11(6):943-6
references.pmid: 15963293
references.citation: Emerg Infect Dis. 2011 Jan;17(1):7-15
references.pmid: 21192848
references.citation: Drug Discov Today. 2005 Sep 15;10(18):1245-52
references.pmid: 16213417
references.citation: J Bacteriol. 2010 Nov;192(21):5767-77
references.pmid: 20833811
references.citation: Nucleic Acids Res. 2001 May 1;29(9):e45
references.pmid: 11328886
references.citation: J Bacteriol. 2007 Jul;189(13):4587-96
references.pmid: 17483226
references.citation: J Antimicrob Chemother. 2004 Jun;53(6):997-1003
references.pmid: 15150175
references.citation: Neurosci Lett. 2003 Mar 13;339(1):62-6
references.pmid: 12618301
references.citation: Int J Syst Bacteriol. 1997 Oct;47(4):1253-4
references.pmid: 9336938
references.citation: Proc Natl Acad Sci U S A. 1992 Mar 1;89(5):1847-51
references.pmid: 1311853